Seasonal abundance of defoliating lepidopterous larvae and predaceous arthropods and simulated defoliator damage to peanuts

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Seasonal abundance of defoliating lepidopterous larvae and predaceous arthropods and simulated defoliator damage to peanuts
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Peanuts -- Diseases and pests -- Florida   ( lcsh )
Lepidoptera -- Control   ( lcsh )
Lepidoptera -- Control   ( fast )
Peanuts -- Diseases and pests   ( fast )
Florida   ( fast )
Entomology and Nematology thesis Ph. D
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Thesis--University of Florida.
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Includes bibliographical references (leaves 101-108).
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Typescript.
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Vita.
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by John Robert Mangold.

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SEASONAL ABUNDANCE OF DEFOLIATING LEPIDOPTEROUS LARVAE AND PREDACEOUS ARTHROPODS AND SIMULATED
DEFOLIATOR DAMAGE TO PEANUTS























By
JOHN ROBERT MANGOLD














A DISSERTATION PRESENTED'II) TO TIlE GRADUATE COUNCIL, OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE
OF DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA

1979
















ACKNOWLEDGEMENTS


The author wishes to acknowledge his sincere appreciation to Dr. S. L. Poe, research advisor and chairman, for his patience and assistance throughout the course of this study. Special appreciation is extended to the supervisory committee, Drs. J. W. Jones, C. A. Musgrave, D. H. Habeck, and C. S. Barfield for advice and critical reviews of the dissertation.

The author wishes to express his gratitude to the

Department of Entomology and Nematology and in particular to Stephanie Burgess, Gail Childs, Micky Hartnett, Donna Labella, Mike Linker, Carol Lippicott, John O'Bannon, Randy Stoutt, and John Wood for help with field work.

The author also wishes to thank Dr. Habeck for identification of lepidopterous larvae, Skip (Paul) Choate for identification of Caribidae, and Roger Iletzman for identification of Geometridae.


















ii
















TABLE OF CONTENTS


Page

ACKNOWLEDGEMENTS . ................... ii

LIST OF TABLES . .................... v

LIST OF FIGURES. . .................... Vi

ABSTRACT . ....................... viii

INTRODUCTION . . . . . 1

LITERATURE REVIEW. . . . . 5

Foliage Consuming Lepidopterous Pests . 5 Predaceous Arthropods Associated with Peanuts 9 Spatial Distributions of Arthropods ....... 9 Effects of Defoliation on Plant Growth and Yield. 11 SEASONAL DYNAMICS OF DEFOLIATING LEPIDOPTEROUS LARVAE
IN NORTH CENTRAL FLORIDA PEANUTS 1976-1978. . 21

Introduction. . . . . 21
Materials and Methods . . . 22
Results and Discussion. . . . 23

SEASONAL DYNAMICS OF PREDACEOUS ARTIIROPODS IN NORTH
CENTRAL FLORIDA PEANUTS 1976-1978 . . 56

Introduction. . . . . 56
Materials and Methods . . . 57
Results and Discussion. . . . 58

SPATIAL DISTRIBUTION OF DEFOLIATING LEPIDOPTEROUS
LARVAE ON PEANUTS . . . . 72

Introduction. . . . . 72
Materials and Methods . . . 73
Results and Discussion . . . .. 74

EFFECTS OF UNIFORM HAND DEFOLIATION OF PEANUTS ON
PLANT GROWTH. . . . . 78

Introduction. . .................... 78
Materials and Methods . . . 80
Results and Discussion. . . . 83


iii









Page

APPENDIX .. ............. . .... 98

LITERATURE CITED . . .. ... .. 101

BIOGRAPHICAL SKETCH . . . . 109











LIST OF TABLES


Table Page

1. Characteristics of peanut fields used in
survey, Alachua County, Florida, 1976-1978 . 30

2. Relative abundance of lepidopterous larvae
associated with Alachua County, Florida,
'Florunner' peanuts 1976-1978 . . 31

3. Relative abundance of predaceous arthropods
associated with Alachua County, Florida,
'Florunner' peanuts 1976-1978 . . 66

4. Correlation coefficients between lepidopterous
foliage feeding larvae and predaceous arthropods on Alachua County 'Florunner' peanuts .. . 67

5. Percentage fit of counts of foliage consuming
lepidopterous larvae to expected frequency
distributions, 1976-1978 . . . 76

6. Average percent light interception of intact
and defoliated 'Florunner' peanut canopies
after defoliation . . . . 88

7. Regression equations of pod and crop weights
of intact and defoliated 'Florunner' peanut
canopies . . . . . 89

8. Specific leaf weight (SLW) of peanut leaves
from intact and defoliated 'Florunner'
peanut canopies in relation to weeks after
planting . . . . . 90

9. Effect of defoliation of 8 week-old 'Florunner'
peanut plants on plant parts, 2 weeks posttreatment . . . . . 91

10. Effect of defoliation of 'Florunner' peanut plants on plant parts at 19 weeks. ......... 92

11. Dry weight of leaves from intact and defoliated 'Florunner' peanut plants 2 weeks after defoliation . . . . . .. 93

12. Solar radiation, temperature, rainfall and irrigation during growing season, 1978 . . 98




v















LIST OF FIGURES


Figure Page

1. Location of Alachua County,Florida, peanut
fields sampled in survey of peanut arthropods,
1976-1978. ... . . ... . 33

2. Mean numbers of FAW, CEW, and VBC larvae
sampled from Alachua County, Florida, peanuts 1976-1978. Breaks in lines indicate dates
of insecticide application.. .... . 35

3. Mean numbers of FAW larvae sampled from
Alachua County, Florida, 'Florunner' peanuts,
1976-1978. . .. .. . . 43

4. Mean numbers of CEW larvae sampled from
Alachua County, Florida,'Florunner' peanuts,
1976-1978. . . ..... . 45

5. Mean numbers of VBC larvae sampled from
Alachua County, Florida, 'Florunner' peanuts,
1976-1978. . . . . .. 47

6. Mean numbers of VBC, FAW, and CEW larvae
sampled from various age of Alachua County,
Florida, 'Florunner' peanuts, 1976-1978 . 49

7. Mean numbers of Plusiinae looper larvae
sampled from Alachua County, Florida,'Florunner'
peanuts, 1976-1978 . . . . 51

8. Mean numbers of GCW larvae sampled from Alachua
County, Florida, 'Florunner' peanuts, 1976-1978. 53

9. Mean numbers of BAW larvae sampled from Alachua
County, Florida, 'Florunner' peanuts, 1976-1978. 55

10. Mean numbers of ants, spiders, and L. riparia
sampled from Alachua County, Florida, 'Florunner'
peanuts, 1976-1978 . . . . 69

11. Mean numbers of Geocoris spp., nabids, and 0.
insidiosus adults sampled from Alachua County,
Florida, 'Florunner' peanuts, 1976-1978 ....... 71


vi










Figure Page

12. Quadratic regression of percent light interception to LAI of defoliated and intact peanut
canopies, ** significant at -" =0.01 level,
and significant at c- =0.05 level. . . 95

13. Dry matter accumulation in peanut plant parts
in relation to weeks after defoliation. Pod weight is adjusted by factor of 1.88 X kernel
weight . . . . . . 97
















































vii
















Abstract of Dissertation Presented to the Graduate Council of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

SEASONAL ABUNDANCE OF DEFOLIATING LEPIDOPTEROUS LARVAE AND
PREDACEOUS ARTHROPODS AND SIMULATED
DEFOLIATION DAMAGE TO PEANUTS By

John Robert Mangold

December, 1979

Chairman: Sidney L. Poe
Major Department: Entomology and Nematology

A survey of lepidopterous larvae on north central Florida peanuts detected 27 species during 1976-1978. The most abundant larvae were velvethean caterpillar, Anticarsia gemmatalis (Hubner), fall armyworm, Spodoptera frugiperda (J. E. Smith), corn earworm, Heliothis zea (Boddie), Plusiinae loopers, granulate cutworm, Feltia subterranea (Fabricius), and beet armyworm Spodoptera exigua (Hubner). Only the former 3 species of larvae reached damaging levels.

Fall armyworm larvae were most abundant during mid-July

to early August when peanuts were 12-17 weeks old. Corn earworm larvae were most numerous in mid-July when peanuts were ca. 12 weeks old. During August through early October velvetbean caterpillar larvae were most abundant on peanuts 15-17 weeks old.

The most abundant and important predators surveyed in peanuts were ants, spiders, Labidura riparia (Pallas),



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Geocoris spp. nabids, Orius insidiosus, and ground beetles. Ants were abundant and probably important predators throughout the season. Spiders were common predators for the entire season. Labidura riparia numbers increased rapidly during the season to greatest numbers at the season's end. Geocoris spp. and nabids were abundant from mid-August to September then declined in number late in the season. Peak abundance of

0. insidiosus occurred during mid-June and early July, then declined sharply.

Correlation coefficients between predators and foliage feeding larvae indicated nabid abundance was closely associated with velvetbean caterpillar numbers. Spiders, L. riparia, Geocoris spp. and 0. insidiosus were also associated with larval numbers.

The spatial distributions of fall armyworm, corn earworm, velvetbean caterpillar, Plusiinae loopers, and granulate cutworm were fit to 6 frequency distribution models. The common k values calculated for the 5 species were 3.93, 5.20, 7.27,

2.57, and 3.58 respectively. Only the first 2 common k
2
values significantly fit (P=0.05) a v test for homogenity of k.

Uniform hand defoliation of peanut canopies at 4 levels reduced yield of peanuts. Increases in specific leaf weight and decreases in light interception of defoliated canopies were recorded. Quadratic regressions of light interception as a function of leaf area index were calculated for defoliatal and intact canopies. Plants defoliated 75%0 at 8 and 11 weeks after planting compensated for defoliation by growing ix










significantly more leaves than undefoliated plants. Plants defoliated 75% at 8 weeks also decreased stem growth. Defoliation also reduced crop and pod growth rates of defoliated plants compared to undefoliated plants.




















































X
















INTRODUCTION

The increasing world population has focused our attention on high protein food plants among which is Arachis hypogea L., the groundnut or peanut. Leading producers of peanuts by acreage are: India 35%, China 15%, United States 8%, Nigeria 8%, and Senegal 7% (Janick et al. 1974). Approximately 650,000 ha of peanuts are produced annually in the United States. Peanuts rank ninth in acreage among major field crops and second in dollar value per acre in the United States (McGill et al. 1974). The distribution of peanut acreage allotments in the United States is: Georgia 33%, Texas 23%, Alabama 14%, North Carolina 11%, Oklahoma 9%, Virginia 7%, Florida 4%, and South Carolina 1% (McGill et al. 1974).

Peanuts are one of many crops in Florida's diversified agriculture. The Florida peanut acreage is ca. 22,270 ha of which 3,080 ha are in the state's north central peanut growing belt centered in Alachua, Levy, and Marion Counties (USDA 1977).

Most insecticide applications on peanuts in the southeastern United States are made to control foliage consuming lepidopterous larvae (French 1973). Pilot pest management programs have demonstrated that insecticide usage can be





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substantially reduced with weekly population assessment and economic thresholds as a guideline for insecticide application (French 1975). The economic thresholds currently in use are based on limited data from defoliation experiments, larval consumption data, and principally on experience.

Among the first steps toward the implementation of a

pest management program are the determination of the insect pest species present in peanut fields and the evaluation of their effect upon the crop. In the United States the peanut pest complex varies with locality necessitating regional surveys. A knowledge of the regular, occasional, and potential pests in a particular area is necessary before steps can be taken to control them with timely usage of insecticide.

The seasonal dynamics of defoliating lepidopterous insects on peanuts in Florida has not been documented. Seasonal occurrence information for populations described in the literature from other states is based primarily on experience and not on long term studies. Data relating plant age to numbers of foliage feeding larvae have not been

published, but are necessary for determining which plant ages should be critically studied in relation to defoliation.

Foliage consuming larvae considered important in the

southeastern United States include fall armyworm, Spodoptera frugiperda (J. E. Smith), corn earworm, Heliothis zea Boddie, velvetbean caterpillar, Anticarsia gemmatalis Hubner, granulate cutworm, Feltia subterranean (Fabricius), and beet armyworm, Spodoptera exigua (llubner) (Bass and Arant 1973).




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The use of natural control agents such as predators and parasites is ideally maximized in a pest management program. The parasite complex of lepidopterous larvae on Florida peanuts has previously been discussed (Nickle 1977) however, no description of the predaceous arthropod complex on peanuts in the southeastern United States has been reported. Any understanding of the biotic potential of both major and minor pests is impossible without an analysis of the predator complex in the crop.

Better quantification of the relationship of defoliation to yield loss is needed to further define defoliation levels at which treatments are needed. A systems approach to peanut plant growth and development as affected by defoliation is being pursued to develop models that can realistically simulate the dynamic nature of insect defoliation and plant growth (Barfield and Jones 1979). Most previous defoliation experiments have emphasized defoliation effects on final yields, but ignored how defoliation caused the observed effect. Confounding environmental effects such as drought stress and the presence of other pests such as Cercospora leafspot have often made defoliation experiments less meaningful.

The objectives of the research reported here were to:

1. describe the s(,asonal occurrence of foliage
consuming lepidopterious larvae on peanuts in
north central Florida

2. determine the seasonal occurrence of predaceous
arthropods in north central Florida peanuts




4




3. determine the spatial distribution of foliage
feeding lepidopterous larvae on Florida peanuts

4. examine the effect of simulated defoliator
damage on peanuts using plant growth analysis
















LITERATURE REVIEW


Foliage Consuming Lepidopterous Pests

The arthropod fauna associated with peanuts in the United States is composed of endemic and introduced species that have adapted secondarily to this plant of South American origin. Thus, as a rule, arthropods infesting peanuts in North America are not specialized feeders, and their relative importance as peanut pests often is in inverse correlation to the availability of alternate preferred hosts.

The peanut plant is damaged by a variety of arthropod

pests in the United States. In the southeastern peanut belt most insecticide applications are made to control foliage feeding lepidopterous larvae (French 1973). Typically insecticides are applied 0-4 times per field to kill foliage feeding larvae. Foliage feeding larvae of major economic significance in the Southeast include fall armyworm, Spodoptera frugiperda (J. E. Smith), corn earworm, IIeliothis zea (Boddie), velvetbean caterpillar, Anticarsia gemmatalis (Hubner), and granulate cutworm, Feltia subterranea (Fabricius). Other arthropods of major economic importance in Florida include lesser cornstalk borer, Elasmopalpus lignosellus (Zeller) and spider mites.



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The fall armyworm is a periodic defoliator of peanuts in the southeast. Some feeding damage occurs every year and frequently sufficient number of larvae are present to completely defoliate plants in outbreak years (Bass and Arant 1973). Consequently, severe damage to peanuts in southeastern Alabama and southwestern Georgia has been reported (Arant 1948a). In Oklahoma, fall armyworm was reported numerous in some areas on peanuts during October, but damaging populations were not common in 1972-1974 (Wall and Berberet 1975).

The corn earworm usually causes light to moderate

damage. Occasionally severe infestations occur and complete defoliation of plants occurs (Bass and Arant 1973). In a 2 year study in Georgia, Leuck et al. (1967) found indices of foliage ragging by corn earworm damage were negatively correlated with yield. Morgan (1979) reported corn earworms were most damaging during early August in Georgia. Wall and Berberet (1975) found corn earworm was one of the 2 most common foliage feeders collected in Oklahoma. The corn earworm is the most common insect defoliator on peanuts in the West Cross Timbers area of Texas although populations usually are not economically damaging (Sears and Smith 1975).

The velvetbean caterpillar also causes damage to

peanuts every year in Alabama, Florida, and Georgia (Bass and Arant 1973). Damaging populations of velvetbean caterpillars are not common in Oklahoma although larvae may become numerous in October (Wall and Berberet 1975). Velvetbean





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caterpillar is one of the few peanut defoliators that have been experimentally proven to significantly reduce yields. English (1946) applied insecticides for velvetbean caterpillar populations in Alabama and reported 9-65% yield reductions in untreated plots. Arant (1948b) demonstrated that velvetbean caterpillar defoliation caused 20-43% yield losses from untreated Alabama peanuts.

The granulate cutworm damages peanuts by feeding on

foliage and underground parts. When infestations are severe, portions of leaves and stems may be cut from the plants. In Georgia damaging infestations may occur from late June until early August, but are most frequent about mid July when as many as 11 larvae per row foot may be present (Morgan and French 1971). Three generations of granulate cutworm on peanuts have been recorded from Georgia (Bass and Johnson 1978). Cutworm populations peak in late June, late July, and again in late August: the last generation is usually the most noticeable and damaging.

The beet armyworm, Spodoptera exigua (Hubner) is a

minor foliage feeding pest that infrequently causes damage. A few instances of serious defoliation have been reported (Bass and Arant 1973).

Larvae of the rednecked peanutworm, Stegasta bosqueella (Chambers) may cause minor damage (Bass and Arant 1973). Feeding is confined to unopened leaves and the meristematic region of buds and thus larvae may retard terminal growth (Arthur et al. 1959). The rednecked peanutworm is the most





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common insect pest of peanuts in Oklahoma (Wall and Berberet 1979). Walton and Matlock (1959) obtained significantly higher yields through use of chemical controls for this pest in Oklahoma, but Arthur et al. (1959) and Bissell (1941) reported that control of this pest did not increase yields in Alabama and Georgia, respectively.

A number of other foliage feeding larvae have been

associated with peanuts. These potentially injurious insects include: the tobacco budworm, IIeliothis virescens (Fabricius); yellowstriped armyworm, Spodoptera ornithogalli (Guenee); the saltmarsh caterpillar, Estigmene acrea (Drury); the yellow wollybear, Diacrisia virginica (Fabricius); green

cloverworm, Plathypena scabra (Fabricius); cabbage looper, Trichoplusia ni (Hubner); soybean looper, Pseudoplusia

includes (Walker); cotton square borer, Strymon melinus (Ilubner); Platynota nigrocerrina Walsingham; and Argyrogramma verucca (Fabricius) (Kimball 1965, Canderday and Arant 1966, Tietz 1972, Wall and Berberet 1975, Smith and Jackson 1976, Martin 1976).

There is a paucity of published information on the seasonal abundance of foliage feeding larvae. Sears and Smith (1975) developed a partial monthly life table for corn earworm on Texas peanuts. Greatest larval numbers occurred during July. Weekly averages of foliage feeding larvae in 1972 for 4 Georgia peanut fields were reported by French

(1974). Granulate cutworms, corn earworms, and fall armyworms comprised 77,0 of the larvae sampled, but seasonal fluctuations for individual species were not given.





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Predaceous Arthropods Associated with Peanuts

Knowledge of the seasonal and relative abundance of

predaceous arthropods is helpful in defining their role in regulating pests of peanuts. With the exception of a report of striped earwigs, Labidura riparis (Pallas) collected in pitfall traps in Florida peanuts (Travis 1977), there have been no studies of seasonal incidence or relative abundance of predators in peanuts. Martin (1976) found Coleomegilla maculata (De Geer) and Geocoris punctipes (Say) the most numerous predators in small peanut plots in north Florida; and spiders were present in low densities.

Predaceous insects most commonly found in Texas peanut fields are lady bugs, assassin bugs, lace-wings, ground beetles, predaceous stink bugs, Geocoris spp., Nabis, Orius, and praying mantids (Smith and Hoelscher 1975). Spiders were one of the more numerous predators sampled in a study of the effect of insecticide placement on nontarget organisms in Texas peanuts in 1972-1973 (Smith and Jackson 1976).


Spatial Distributions of Arthropods

The method of sampling for foliage feeding lepidoptera

larvae has been manual shaking of plant branches onto a ground cloth similar to the method of sampling soybeans developed by Boyer and Dumas (1963). The foliage shaking sample method has been used extensively in Georgia, Florida, Alabama, and Texas and economic thresholds are based on sampling results obtained with it. In North Carolina a standard sweep net is recommended for population estimation (Stinner et al. 1979).




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Recent emphasis on accurate sampling procedures for

insects in peanuts has revealed the need for better definition of the spatial distribution of these insects. Also, knowledge of spatial patterns provides insight into the biology of the species in question. Data on the spatial distribution of insects is necessary before development of sequential sampling schemes may be effected (Waters 1955).

Spatial distribution models are probability distributions that relate the frequency of occurrence of an event, depending on the mean of the measurements and in some cases on one or more parameters.

The most useful statistical distributions in entomological research have been the Poisson and negative binomial (Southwood 1978). The Poisson distribution describes a

random distribution with variance equal to the mean. In insect sampling the variance most commonly will be larger than the mean, indicating that the distribution is aggregated or clumped. The most useful distribution describing a clumped insect population has been the negative binomial. The versatility of this distribution arises from the fact that it may arise from at least 5 different models (Waters and Henson 1959).

The probabilities of a Poisson distribution are given by
Se L x = 0, 1, 2,..
x xl
where Px is the expected proportion in the xth class and x = 0, 1, 2, is the value of a discrete random variable.





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The mean and variance of the distribution are equal toic. The usual procedure is to make a number of observations and the mean of these, x, provides an estimate of/Land r2.

The negative binomial is defined by 2 parameters, the mean and a positive exponent k. The distribution is generally expressed by the expansion of


(q-p) where k)0, p= /, and q= l+p.

The expansion of the probability is given by


p = (k + x -1) px x = 0,1,2,.
x x (k -1) qk + x

With increasing randomness, the variance of the distribution approaches the mean and the Poisson more accurately describes

the distribution.


Effects of Defoliation on Peanut Plant Growth and Yield

Typically, peanuts in Florida are planted from early

April to late May; in exceptional years spring droughts delay some planting until June. 'Florunner', released in 1969, is the most widely grown peanut cultivar in the United States. Over 80'% of the peanuts grown in Florida are 'Florunner'

Peanuts exhibit an indeterminate growth pattern. The plant growth of 'Florunner' is prostrate with the typical

sequential branching pattern of Virginia type varieties-i.e. alternate pairs of reproductive and vegetative nodes

on laterals and no reproductive nodes on main stems.

'Florunner' peanuts grown under normal conditions in Florida begin flowering at ca. 30 days after planting; peak




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flowering occurs at 60 days. After 80 days flowers are no longer present (McCloud 1974, McGraw 1977). The seasonal flowering pattern has a frequency curve similar to a normal distribution. Pegs begin to appear ca. 7-14 days after flowering. Generally only 15-30% of the flowers produce mature pods (Smith 1954). Early pegs generally produce a higher proportion of fruit than pegs initiated later. Usually by 56 days after planting the first pegs begin to swell into pods. Pod number per plant increases steadily until ca. 84 days at which time the pod load stabilizes. By day 70, seeds begin filling. Pod formation is completed soon after the full pod load is established and growth thereafter is in the seed (Duncan et al. 1978). The pegs and pods which fail to mature remain attached to the plant and are not eliminated

by abscission (Smith 1951).

McGraw (1977) used plant growth analysis to describe 'Florunner' growth as follows: Plant growth followed a sigmoid curve. The first 7 weeks of vegetative growth was geometric. All assimilates were used for accumulation of dry matter into vegetative parts. The largest component in terms of dry matter during this phase was the leaf component.

There was a linear growth phase which extended from week 7 to week 16. At 10 weeks plant. development shifted from vegetative to reproductive growth and the rate of dry matter production began to slow since more photosynthate production was required for seed production than vegetative matter. Dry matter accumulation in the stem and leaf component ceased at about 84 days. The pods filled at a linear rate until maximum dry weight was reached at day 133.




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Duncan et al. (1978) calculated the crop growth rate of 'Florunner' from the same data used by McGraw. Linear regression of crop dry weights from canopy closure at 55 days until seed growth became significant at 70 days determined that the crop growth rate was 21.2g/m2/day. This was assumed to be the period of maximum crop growth rate.

Partitioning was used by Duncan et al. (1978) to

refer to the division of daily assimilate between reproductive and vegetative plant parts. The partitioning factor may be calculated by comparing the fruit and vegetative growth rates. A correction is made for the fruit growth rate to account for the additional energy expenditure of seed production. Correction factors developed by Hanson et al. (1961) and Penning de Vries (1974) are used to compensate for the higher concentration of oils and proteins in seeds. Duncan et al. (1978) estimated partitioning by 2 methods for 'Florunner'. From comparison of crop and corrected fruit growth rates the reproductive partitioning factor was calculated as 84.7%. The value for the reproductive partitioning factor estimated from simulations of the PENUTZ model was 72% (Duncan et al. 1978).

Two useful terms often used to describe plant canopies are leaf area index (LAI) and percent ground cover. Percent

ground cover is the percent of soil surface that is covered by the crop canopy. The LAI is defined as leaf area per

unit of ground area and does not indicate directly the amount of solar radiation intercepted by the canopy. Larval





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consumption rates of leaf tissue can, however, be easily coupled to LAI. Measurement of percent light interception and LAI of canopies are both needed for describing the structure of defoliated and intact canopies. For example, Rudd et al. (1979) used the light interception--LAI relationship of soybean, Glycine max L. (Merr.) determined by Shibles and Weber (1965) to model soybean insect defoliation in a dynamic model of soybean growth and yield.

McGraw (1977) found that ground cover of peanuts

increased geometrically from 10% at 3 weeks to 100% at 8 weeks after planting and remained 100o until harvest. The LAI increased from 0.11 at. 3 weeks to 1.5 at 7 weeks. At

8 and 10 weeks the LAI had reached 3.G and 5.6, respectively. After 10 weeks the LAI maintained an average of 5.6 for 5

weeks until Cercospora leaf spot partially defoliated the canopy.

There have been several reported defoliation experiments of various varieties of peanuts with very inconsistent yield

reductions (King et al. 1961, Greene and Gorhet 1973, Enyi 1975, Williams et al. 1976, Campbell unpubl. Nickle 1977). Results generally demonstrate that defoliation at early podfill, 8-12 weeks after planting, causes the most serious yield losses.

King et al. (1961) simulated defoliator damage by

mechanical removal of leaf canopy from the top 1/3 2/3's


Dr. W. V. Campbell, professor of entomology, North Carolina State University, Raleigh.





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of irrigated and dryland peanuts in Texas. Seventy-five percent defoliation of 56-day-old plants and 50% defoliation of 75-day-old plants did not affect yields of irrigated peanuts. Thirty-three percent defoliation did not significantly reduce yields of 53- and 94-day-old plants, but higher defoliation levels did reduce yield of dryland peanuts.

A mowing machine was used by Greene and Gorbet (1973) in a 3 year study to approximate 5 levels of defoliation of 'Florunner' peanuts in Florida. Removal of ca. 33% of leaf area reduced yields at most growth stages; yield was reduced more when defoliation was delayed. Yield losses ranged from 1.8-7.4%, 3.7-32%, 8.6-44% and 34-63% for defoliation levels of 10-15, 20, 33, and 50%, respectively. Some reproductive branches and pegs were removed at the 50% defoliation level.

Enyi (1975) hand defoliated 'Dodoma' edible peanuts at

2 week intervals at 3 levels in Tanzania. Defoliation levels of 50 and 100% reduced pod and stem weight, and kernel size. Greatest yield losses occurred to plants defoliated ca. 1 week after early podding stage. It appeared that defoliation reduced pod number by slowing stem growth which resulted in a reduction in number of flowering nodes.

Williams et al. (1976) dleternined growth rates of plant parts of 'Makulu Red' peanuts in Rhodesia. Defoliation levels of 50 and 75% were achieved by removal of 2-3 leaflets per tetrafioliate. Compared to the untreated check, defoliation





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de creas e d c r (p growth rate 2 weeks after defoliation by 17-42%. Stem and pod growth rates were also decreased by defoliation.

Campbell (unpubl.) used hand shears to clip leaves

from unirrigated peanuts in North Carolina. Yield reductions started with 50% defoliation on 15 July and 15 September, and 20% defoliation on 1 September, and 10% defoliation on 1 and 15 August.

Unirrigated 'Florunner' peanuts were hand defoliated

at 5 levels at 2 locations in north central Florida (Nickle 1977). Yield reductions in both plots were most severe at 63 days after cracking. Yield reductions averaged 2-6.8, 7.2-21.6, 16.8-41.2, and 20-51% from 25, 50, 75, and 100% defoliation, respectively for the 2 defoliation experiments. Peanut quality was also reduced by some defoliation treatments.

Too often researchers have studied the effect of defoliation only in terms of the final harvest. Growth analysis is a useful tool in the quantitative analysis of plant growth. Generally 2 assessments are required to carry out a simple growth analysis of plants with a closed canopy-i.e., dry weights of plant material per unit area of ground and LAI of the canopy (Radford 1967). Knowledge of the time and rate of dry matter accumulation is vital to understanding the physiology of any crop and is particularly amenable to studying the effect of defoliation.





17



Previous defoliation studies have examined only the effect of defoliation on final yield or limited growth rate changes caused by defoliation. One of the few papers reporting canopy characters and photosynthesis of defoliated peanuts was that of Boote et al. (1980). Defoliation of 75% of the upper 42% of the canopy leaf area of unirrigated 'Early Bunch' peanuts corresponded to 25% of the total leaf area and reduced light interception from 95.6 to 74%. Canopy carbon exchange rate was reduced 35% from 20.2 mg C02/dm2/h to 13.1 mg C02/dm2/h and uptake of 14CO2 was reduced by 30%.

Nickle (1977) questioned the relevancy of manual

excision of peanut leaflets in establishing crop damageyield relationships, manual leaf removal was thought to be more stressful than larval defoliation. However, Thomas et al. (1979) demonstrated good agreement in yield losses between manual soybean leaflet removal and defoliation by caged cabbage looper, T. ni.

Removal of a fixed proportion of leaflets per tetrafioliate throughout the canopy has a further disadvantage in that it may not realistically simulate the effect of insect defoliation in terms of canopy damage site. The early instars of soybean looper on soybeans are reported to feed selectively on low-fiber containing leaf tissues of terminal leaves. The later instar larvae feed on non-terminal leaves (Kogan and Cope 1974). Similar observations of corn earworm larval damage to peanuts were reported by Huffman





18



(1974) and Morgan (1979). The last 2 instars of noctuid larvae consume 80-91% of the total consumed foliage (Snow and Callahan 1968, Nickle 1977). Most researchers have assumed terminal bud damage is minor compared to the much greater potential loss of older foliage.

Surveys of foliage feeding larvae on peanuts in 1976 indicated that peanuts 11-19 weeks old were most often attacked by defoliators (Mangold et al. 1977). Terminal damage at this time is probably not of major significance since the majority of leaf matter is present. Sustained terminal bud damage to younger plants during the geometric vegetative growth stage may be an important aspect of defoliator damage by corn earworm and possibly fall armyworm.

A systems approach to the effect of defoliation on

peanut growth and yield is being pursued (Barfield and Jones 1979). There are currently 3 peanut plant models. Two of the models lack appropriate mechanisms for coupling defoliation to peanut growth and development (Duncan 1974, Young et al. 1979). The third model, by Smith and Kostka (1975) is based on yield loss and larval consumption rates and is not general enough for studying the dynamics of insect defoliation on plant growth.

Based on limited dclfolialion experiments, larval consumption data, and principally on experience, an economic threshold of 4 or more foliage feeding larvae per row foot was used in a pilot pest management program in Georgia in





19



1972-1974 (French 1975). In 1974 the Georgia pilot program reduced applications from an average of 2 per field for defoliators to an average of 0.05 per field in the program's 114 fields. Sampling 7.6 m of row for defoliators by shaking the branches and the empirical threshold were responsible for the reduction in insecticide usage (French 1973).

In 1975 the Tri-States Pest Management Project was

initiated on corn, soybeans, and peanuts in Georgia, Alabama, and Florida. Shake cloths were used to sample 0.91 m sections of row for defoliators. An action threshold of 4 larvae per row foot was used before early August but later increased to 6 larvae per row foot after early August (Linker and Johnson 1978).

In Texas, field observations and limited research data indicate 3-5 and 6-8 medium to large larvae per row foot

can be tolerated before yield losses will occur on dryland and irrigated Spanish peanuts, respectively (Hoelscher 1977).

Economic thresholds for defoliators on peanuts should be revised. The concept of economic threshold is very useful in the primitive state of the art. The economic threshold refers to the pest population density at which active control

measures should be initiated to prevent the post from reaching the econoinic injury level. The economic injury level is the lowest number of insects that will cause economic damage. However, there are many factors that ideally should determine an economic threshold. Beneficial insects, pest pathogens, plant growth stage, interacting plant pathogens,




20



market prices, weather conditions, farming practices, economics of crop production, pest species, etc., influence the economic threshold. Economic thresholds are useful in providing a guideline to the farmer as to whether it is economical to control a pest.

Defoliation studies indicate that plant age greatly

influences the amount of defoliation that can be tolerated without yield loss. The static nature of current action thresholds does not reflect the dynamics of the impact of defoliation on crop yield. Also, studies on larval consumption rates of peanut leaves demonstrate major differences in relative amounts of foliage consumed among defoliators (Snow and Callahan 1968, Nickle 1977, Huffman and Smith 1979). Future action thresholds should consider the balance of defoliator species involved at the time.
















SEASONAL DYNAMICS OF DEFOLIATING LEPIDOPTEROUS LARVAE IN
NORTH CENTRAL FLORIDA PEANUTS 1976-1978 Introduction

In the southeastern United States most insecticide applications on peanuts have historically been made to control foliage consuming lepidopterous larvae (French 1973). Foliage feeding larvae reported reducing yields in the southeastern United States include fall armyworm, Spodoptera frugiperda, (J. E. Smith); corn earworm, Heliothis zea (Boddie); velvetbean caterpillar, Anticarsia gemmatalis (Hubner); and granulate cutworm, Feltia subterranea (F.) (Bass and Arant 1973).

Practically no information is published on the seasonal occurrence of foliage consuming lepidopterous larvae on peanuts. Sears and Smith (1975) developed a monthly life table for corn earworm on Texas peanuts. Weekly averages of foliage feeding larvae for 4 Georgia peanut fields in 1972 were reported by French (1973), however; seasonal fluctuations of individual pest species were not given. The seasonal occurrence of foliage feeding lepidopterous larvae on peanuts in north central Florida was studied in 1976-1978 and the results are reported here.




21




22




Materials and Methods

A total of 14 Alachua County, Florida, growers' fields

planted to 'Florunner' peanuts were surveyed during 1976-1978 for relative densities of lepidopterous larvae (Table 1). Samples were taken at weekly intervals starting on 6 July, 15 June, and 23 June in 1976, 1977, and 1978, respectively, and continued until harvest. A total of forty 0.91 m of row samples were taken at each sample date by the ground cloth method.

Samples were taken by folding back the branches and gently placing a ground cloth 0.91X 0.91 m against plant bases of one side of the row. The peanut canopy was beaten downward vigorously with forearm and hands 6 to 8 times over the cloth to dislodge arthropods. Arthropods that were observed either under the branches while inserting the ground cloth or on the ground cloth were identified, counted, and recorded.

In 1976-1977 samples were taken throughout each field in a manner similar to that used by commercial scouts. All areas of the field were sampled in a random manner with not more than 10% of the samples within ca. 20 m of any field edge. In 1978 samples were taken along the transects of an X-shaped pattern which was aligned along the diagonals of the field. Twenty samples per transect were taken every tenth row in Field M and every thirteenth row in Field N. Each week sampling began on a different row.





23



The fields surveyed in this study were all in Alachua County in the vicinity of Archer, Florida (Fig. 1) on the southern edge of the southeast peanut belt. Approximately 3,080 ha or 14% of Florida's peanut acreage is in north central Florida. Vegetation surrounding the study sites was mainly woods and pasture with limited acreages of field corn and rarely soybeans.

Some of the fields surveyed were adjacent. The adjacent fields sampled were: (1) C and D; K and L; and B, I, and J. Also Field E was located less than 1 km from I and J.


Results and Discussion

The following 27 species of lepidopterous larvae were associated with Alachua County peanuts: Arctiidae: Diacrisia virginica (Fabricius) and Estigmene acrea (Drury); Gelechiidae: Stegasta bosqueela; Geometridae: Anavitrinella pampinaria Guenee and Cyclophora serrulata (Packard); Lycaenidae: Strymon melinus (Hubner); Noctuidae: Anicla infecta (Ochsenheimer), Anticarsia gemmatalis, Argyrogramma verruca (Fabricius), Elaphria nucicolora (Guenee) Elaphria grata Hubner, Feltia subterranea, IIeliothis virescens (Fabricius), -. zea. Pseudaletia unipuncta (Haworth), Pseudoplusia includens (Walker), Spodoptera eridania (Cramer), S. exigua, S. dolichos (Fabricius), S. frugiperda, S. latifascia (Walker), S. ornithogalli (Guenee), and Trichoplusia ni (Hubner); Pyralidae: Elasmopalpus lignosellus (Zeller); Pieridae: Eurema lisa (Boisduval and Leconte); and Tortricidae: Platynota flavedana Clemens and Sparganothis





24



sulfureana (Clemens). The total numbers of less numerous lepidopterous species were: 53 E. lignosellus, 15 E. acrea,

8 S. melinus, 6 S. bosqueela, 6 E. nucicolora, 5 A. pampinaria,

4 E. grata, 3 A. infecta, 3 P. unipuncta, 3 E. lisa, 2 P. flavedana, 2 P. virginica, and 1 C. serrulata. S. sulfureana larvae were collected only from buds and were not observed in beat cloth samples.

Twelve of the 27 lepidoptera larvae associated with peanuts are new records: A. infecta, A. pampinaria, C. serrulata, E. lisa, E. grata, E. nucicolora, P. flavedana, P. unipuncta, S. sulfureana, S. dolichos, S. eridania, and S. ornithogalli. With the exception of P. unipuncta, A. infecta, and E. grata some larvae of the other 9 species were reared to adults on peanut foliage.

Every year the 3 most abundant lepidopterous larvae

were velvetbean caterpillar, corn earworm, and fall armyworm (Table 2). Plusiinae loopers were common in 1976 and 1978, but not in 1977. Beet armyworm was more numerous in 1977 than in other years. Beet armyworms were also extremely numerous on soybean seedlings in 1977 in Florida (Anon. 1977a, Anon. 1977b).

Population levels of fall armyworm (FAW) were highest, reaching 17 per sample in Field HI on 4 August, during mid July to early August in 1976 (Fig. 2). Field Ii was the only field where FAW larvae were the major pest that required treatment. In the other fields surveyed in 1976, fall armyworm larvae peaked at 0.5-3.8 larvae per sample with the





25



exception of Fields C and D where 9 larvae per sample were present the first week of August (Fig. 2). In 1977 larvae began to be abundant in mid-June in Field K and reached highest levels in Fields K and L in mid-July (Fig. 2). The early June abundance of FAW larvae on peanuts in Field K is probably an indication of the outbreak of FAW reported throughout the Southeast in 1977. In 1978 population levels of FAW were low, peaking at 0.6 larvae per sample and 3.1 larvae per sample on 20 July in Field M and Field N, respectively.

Larvae of FAW were less numerous in 1978 than in 1976 and 1977 (Fig. 3). In fields not treated with insecticides during July a natural decline of FAW larvae occurred during early to mid-August. In no instances were FAW larvae numerous after mid-August.

Rearing of Ileliothis spp. larvae on artificial diet

indicated ca. 95% of the IIeliothis in 1976-1977 were H. zea (Nickle and Mangold, unpubl.). In 1976 the greatest numbers of corn earworm (CEW), 8.4 per sample, occurred in Field F on 21 July (Fig. 3). The range of maximum densities in other fields surveyed in 1976 was 0.6-4.6 per sample. In 1977 CEW attained very high levels of 19 per sample on 20 July in Field L (Fig. 3). The late planted Field L was probably an exceptionally attractive oviposition site for CEW moths because peak flowering occurred during early July at a time when moths were emerging from field corn. Corn earworm has demonstrated a preference for the flowering





26



stage of 4 of its major agricultural hosts in North Carolina (Johnson et al. 1975). In 1978 CEW densities reached their highest levels of 0.6 and 3.1 in mid-July in Fields M and N, respectively.

The patterns of seasonal abundance of CEW for 19761978 were very similar (Fig. 4). In all 3 years CEW larvae were most numerous the third week of July. In fields not treated with insecticides during July, a natural decline of larvae occurred during late July. Corn earworm larvae were never numerous after mid-August.

Velvetbean caterpillar (VBC) larvae were first detected in peanut fields the second week of July. Velvetbean caterpillar was the only pest that demonstrated resurgence after insecticide application (Fields B, G, II, Fig. 2). The dynamics of VBC resurgence appear very similar to the resurgence of the same species observed on soybeans (Shepard et al. 1977). In 1976 VI3C larvae were most numerous in Field G where 36 larvae per sample were counted on 8 September. Very low numbers of larvae were present in the fields planted early in April; maximum VI3C densities ranged from

0.05-0.60 larvae per sample. Maximum larval densities ranged from 0.7 to 7.1 per sample in Fields K and L,

respectively in 1977. Highest levels of VBC larvae in 1978 were 8.0 and 2.3 per sample in Fields M and N, respectively.

In 1977 VBC larvae increased in number ca. 2 weeks

later than in 1976 and 1978 (Fig. 5). In no instances were





27



VBC larvae present in numbers greater than 1 per sample until August. Velvetbean caterpillar larvae were the only numerous insect pest from mid-August through early October.

Adjacent fields of similar planting dates had similar

patterns of larval abundance in terms of timing and density-i.e. Fields C and D; and E, I and J. In the 2 cases where planting dates of adjacent fields differed 4-5 weeks, later planted fields had higher larval densities. The late planted Field B, adjacent to Fields I and J, had 5 times more velvetbean caterpillar the third week of August. Similarly, the very late planted Field L had 8 times more velvetbean caterpillar than the adjacent Field K on 2 September. Also corn earworm numbers were 4 times greater in Field L than Field K on 20 July. Therefore, planting early in north central Florida appears to greatly increase the probability of escape from velvetbean caterpillar problems. Peak numbers of ovipositing adults are probably missed by planting early. Also the older plants may be less attractive as oviposition sites than younger plants.

There were differences in the average numbers of VBC, FAW, and CEW larvae sampled from various age classes of peanuts 1976-1978 (Fig. 6); Field L was not included

because of its atypical planting date. Larvae of VBC were most numerous in peanuts 15-17 weeks old. Larvae o{ FAW fluctuated in abundance, but in general were abundant in peanuts 12-18 weeks old. Larvae of CEW were most abundant in 12 week old peanuts, which is ca. 1-2 weeks after peak





28



flowering. These data indicate that VBC and FAW larval abundance is probably more related to sample date rather than plant age. Corn earworm larval abundance appears to be more equally related to both sample date and plant age, perhaps because CEW prefers to oviposit in flowering fields.

Plusiinae loopers were most numerous from mid-July

through August (Fig. 7). Highest densities of loopers were reached in Field D where 2.3 loopers per sample were present on 18 July. Loopers were the most numerous larvae in Field E.

Granulate cutworm (GCW) larvae demonstrated no clear seasonal trend between years (Fig. 8). In 1977 and 1978 GCW larvae were most abundant in June while in 1976 GCW larvae were most numerous from late July to early August. The lack of clear seasonal fluctuation may be due to the sampling method. Granulate cutworm commonly spend daylight hours buried in the soil and thus are best sampled between 12:00 AM and 5:00 AM (Eden et al. 1964).

Numbers of beet armyworms (BAW) peaked at different

times of the season for the 3 years the survey was conducted (Fig. 9). In 1976 BAW larvae were most numerous during late July while in 1977 and 1978 larvae were most numerous in mid-June and early July, respectively. Beet armyworms were never more numerous than 0.7 per sample during this study.

There were no distinct generations of foliage feeding

larvae on north central Florida peanuts detected in this study. Previously 2-3 generations of velvetbean on soybeans were




29



detected by Menke and Greene (1976) and Strayer (1973). For most species, except for VBC, larvae gradually increased over G-7 weeks, peaked, and then gradually declined over 2-3 weeks. Larvae of VBC in early planted peanuts remained at low numbers throughout the season. In late planted fields VBC larvae were present for 5 weeks or more before a sharp increase in numbers occurred. Decline of VBC except for insecticide intervention on late planted fields was very slight.

The larval development periods of FAW, CEW, and VBC on peanuts are relatively long compared to that of other plant hosts (Huffman and Smith 1979, Nickle 1977). The duration of the larval stage is generally 20-30 days on peanuts compared to 12-25 days on other hosts. Parasitism of larvae of fall armyworm and corn earworm is 20-60%. (Nickle 1977). Predation further reduces survivors. It is possible that peanuts act as a trap crop or a sink for these pests--i.e. few eggs laid by moths survive to the adult stage.














S30






'0 (9 I O 0




0 9 4 o
Sm 0
d0 --- O O 0 m. 0 ) 0 c o E < 0 > _3 E I I





'VO CO I O 0 0 "0 '- C C1 c 1O 0 CD II


0 0 I


MMOOrO H O E O) -H oH o-C o) 0 c0 d 0 m0 0 O 0 0 0c 0)




4-00 OO U) 2O0 O E Q- C C Od




- d 0 L 0 d 0 e4 c4 )





0 C) 000 00 0O GH Ec 0 00 9 04J4
S 1 "I









CO H 0 O LO tO H Cq C CO CO 4-P t od o . r 0 G N Co0 C~ O O .o DO H I IO d



O 11

0 U)

-rI .0 w f'A 0 O
0 Hc3 II


-04 CD N co .2*4' ~ ~ ~ C~
0) 0) 0 H~~k





31









Table 2. Relative abundance of lepidopterous larvae
associated with Alachua County, Florida
'Florunner' peanuts, 1976-1978.


% of total larvae sampled1
Species
1976 1977 1978

Anticarsia gemmatalis 38.7 24.4 52.2 Feltia subterranea 6.1 4.0 3.0 IIeliothis spp. 14.8 42.6 20.5 Plusiinae loopers 10.7 0.6 7.3 Spodoptera frugiperda 25.7 22.4 13.3 Spodoptera exigua 1.6 5.0 0.4 Other Spodoptera spp. 1.5 0.7 1.7 Other 0.9 0.3 1.7


Total number larvae sampled 1976, 1977, and 1978 were 15,661, 3,403, and 1,982, respectively.

































Figure 1. Location of Alachua County, Florida, peanut fields
sampled in survey of peanut arthropods, 1976-1978.






33











I I E











i_ im >- ~ ~ I r-. .











Ti


* (( 5)
() I f/ 4 Pr

































Figure 2. Mean numbers of FAW, CEW, and VBC larvae sampled
from Alachua County Florida peanuts 1976-1978.
Breaks in lines indicate dates of insecticide
application.





35





12

10- Field A
1976
--- FAW

S ........ VBC

4

2


12 Field B L 1976
- 10 S ---FAW
2 ---CEW
4V



U 2

0\
96
3- Field C / CD8 o- 1976
72
6 4 FAW

4 8 ........ VBC
<40
LU32
24
S6
08-


Field D
380 i 976I
7 2
64
5 6- FAW

40
32
24
16 08

JUINE JIlY AUG SEPT


































Figure 2. Continued.





37







425 I 250 Feid 1 /


1 000 -- AW / ...-EWN / \
K........ V i "
0750


0500


0250


0000

8 8 Field F
72

56
< 4 ......... VBC
40
S32
W 24

08 /
00
w 36
33 FdGI (

:D 7
Z 24
21
-CE < 18



6

0
192
176 F ied H



9I W

80 641
48 /
32

00
JiltNL Jhl 1 AUG SE PT


































Figure 2. Continued.




39






26 /
4l- FIEL. DI /\
22 19 6 \
2 0 --FAW


4 \
I 0
08 \
06- \/

02

28
26 FIELD J
24 1976
2 2 -- FAW 20 \ S- CEW / \ C 6 .......... VBC


0 \
08
L o //
04/
02 .
0 0 ...........

4 F FIELD K ::D 40 977 z 6 ---FAW
z ------CEIW
< 24 ........ c
W 2o
V6
1 2
08 /
0 .. ..........

:82
17e F EL) L
160 1 (7
14' FAW 12 8 UL W
112
----CE 31W


64
48
32

00 .... ...
JIINE JIlL AG SEPT



































Figure 2. Continued.





41











8
FIELD M
7- 1978
6- --FAW
w J CEW
1 5......... VBC
! 4

< 3

c 2





2 FIELD N
M44
2 4A- 1978 S4o --FAW Z 36- -CEW Z 3 ........ VBC
28
2.4
20
~I1.612 0 8
04- /
0.0
JUNE JUIY AUG SEPT


































Figure 3. Mean numbers of FAW larvae sampled from Alachua
County, Florida, 'Florunner' peanuts, 1976-1978.





43














7



0 LL
O
0 1976
1977 0 5 ...... 1978


CL









Li\
LL

0
cr4
z> /
u 2


D
z

'Ii




0- JUNE JULY AUG SEPT JUNE JULY AUG SEPT




































Figure 4. Mean numbers of CEW larvae sampled from Alachua
County, Florida, 'Florunner' peanuts, 1976-1978.





45








I0




9

1976
-1977
.......... 1978
8
0 LL
0


a L6









4

0


D 3
Z

ci:
Z

2







0/


JUNE JULY AUG SEPT


































Figure 5. Mean numbers of VBC larvae sampled from Alachua
County, Florida, 'Florunner' peanuts, 1976-1978.




47






I0

I\

9


-- \
8
0 1977 07


97 6-/





_J i <5

> : o /
S4- I

QI





2- ..
CI I




S/




3
JUNE JULY AUG SEPT






















0

*H
Co










co
0





cr









CO
4--)



o o
















E
cd











rb



C












Fr@
'd





49



















cCL















> LLLJ
;> LL








-C







MO JO N 16' J3d 3VAdV9l
H389iN NV31/



































Figure 7. Mean numbers of Plusiinae looper larvae sampled
from Alachua County, Florida, 'Florunner' peanuts,
1976-1978.





51













/ --1976 0 1977 c ........1978
L
8
//


.7
L


a6o /
.J
W,5




o / LL
_5 I LUi




If

O I





IJ

JUNE JULY AUG SEPT



































Figure 8. Mean numbers of GCW larvae sampled from Alachua
County,Florida, 'Florunner' peanuts, 1976-1978.





53
















.8


0C --1976 i.7- 1977 O ........ 1978



O
LU
- 6




,-, /



0

o 2 .2








JUNE JUlY AUG SEPT



































Figure 9. Mean numbers of BAW larvae sampled from Alachua
County, Florida, 'Florunner' peanuts, 1976-1978.





55










.50



.45

0
.40
0 ---1976
S1977 ........ 1978


LL
w

L .30 P< 25



S.20
o I


w
m 15


z.Io I
Z .IO. Lii

.05 : \



.OO
.00 E
JUNE JULY AUG SEPT

















SEASONAL DYNAMICS OF PREDACEOUS ARTHROPODS IN NORTH CENTRAL FLORIDA PEANUTS 1976-1978


Introduction

Peanuts in Florida are damaged by numerous injurious

insects and mites. The most injurious pests in Florida are lesser cornstalk borer, Elasmopalpus lignosellus (Zeller), spider mites, and foliage feeding noctuid larvae. With the exception of data on Labidura riparia (Pallas) collected in pitfall traps in Florida peanuts (Travis 1977) there have been no studies of seasonal incidence of predators. The importance of predators in inducing mortality of pest species has been recognized in other row crops with similar noctuid larval pests such as cotton (Whitcomb and Bell 1964,

van den Bosch and Hagen 1966), and soybeans (Buschman et al. 1977).

There are few reports of incidence of predaceous arthropods in peanuts. Martin (1976) found Coleomegilla maculata (De Geer) and Geocoris punctipes (Say) to be the most numerous predators, with spiders, and 2 reduviids Zelus cervicalis Stal, and Sinea spinipes (HIerrich-Schaffer) present in low densities in small peanut plots in north Florida. Predaceous insects most commonly found in Texas peanut fields are lady bugs, assassin bugs, lace-wings, ground beetles, predaceous




56





57




stink bugs, big-eyed bugs, Nabis, Orius, and praying mantids (Smith and Hoelscher 1975). The objectives of this research were to describe the seasonal incidence, species composition, and relative abundance of predaceous arthropods on peanuts and make preliminary tests of associations between the most numerous predator groupings and major noctuid larval pests.


Materials and Methods

A total of 14 Alachua County, Florida,growers' fields of 'Florunner' peanuts were surveyed during 1976-1978 for relative density of predaceous arthropods. The fields are described in Table 1. Samples were taken at weekly intervals starting on 6 July, 15 June, and 23 June in 1976, 1977, and 1978 respectively, and continued until harvest. A total of forty 0.91 m of row samples were taken at each sample date by the ground cloth method.

Samples were taken by folding back the branches and gently placing a ground cloth 0.91 X 0.91 m against plant bases of one side of the row. The peanut canopy was beaten downward vigorously with forearm and hands 6 to 8 times over the cloth to dislodge arthropods. Arthropods that were observed under the branches while inserting the ground cloth or on the ground cloth were identified, counted, and recorded.

In 1976-1977 samples were taken throughout the field in a manner similar to that used by commercial scouts. All areas of the field were sampled in a random manner with not




58




more than 10% of the samples within ca. 20 m of field edge. In 1978 samples were taken along the transects of an X-shaped pattern which was aligned along the diagonals of the field. Twenty samples per transect were taken every tenth row in Field M and every thirteenth row in Field N. Each week sampling began on a different row.

A test of association between the most abundant predator groupings and lepidopterous larvae was calculated using Kendall's tau-b as suggested by Fager (1957). The Kendall's tau-b statistic is a nonparametric index of order association which conforms to Kendall's criteria for correlation coefficient (Kendall and Stuart 1961).


Results and Discussion

Due to the difficulty of identifying many of the

predaceous species present, certain predators were grouped either in the field or in this report. The composition of the predaceous insect fauna varied considerably with field and year (Table 3). The most numerous predators sampled were ants, spiders, Geocoris spp., L. riparia, nabids, and ground beetles (Table 3). This predator complex comprised 91-99% of the predators sampled.

Ants were often the most numerous predator observed composing from 13- 50' ()f tihe total number sampled. In unsprayed fields ants were generally present in over 75% of the samples. The most commonly observed ant species were Solenopsis geminata (Fabricius), Pheidole spp., and Conomyrma insana (Buckley). Whitcomb et al. (1972)




59




recorded over 60 species of ants from Florida soybeans. Since the crops are grown in the same area and are host to similar pests, the ant fauna of peanuts is probably as complex. Ants were numerous from June through September (Fig. 10).

Considered as a group, spiders composed 9.9-45%

of the predators sampled (Table 3). In most fields spiders did not exceed 20% of total predators sampled except for Fields K, M, and N. In 1978 spiders were classified into 8 categories as follows: 30.4% other spiders; 19% small spider species and immatures; 15.8% wolf spiders (Lycosidae); 12.8% jumping spiders (Salticidae), 7.0% crab spiders (Thomisidae); 5.7% striped lynx, Oxyopes

salticus IHent (Oxyopidae), 5.5% Chiracanthium inclusum (HIentz) and Aysha gracilis Hentz (Clubionidae and Anyphaenidae, respectively); and 3.8% green lynx Peucetia viridans

(Hentz) (Oxyopidae). Spiders were common predators for the entire season and increased in number slowly during the season (Fig. 10).

Big-eyed bugs, Geocoris spp., comprised 2.1-16% of the predator complex. In 1977. 17.97 of the Geocoris counted

were G. ulignosus (Say) adults, 5.7% G. ulignosus nymphs, 38.6% other Geocoris spp. adults, and 37.8' other Geocoris spp.nymphs (n=352). In 1978, G. ulignosus adults comprised 24.9% of the total, G. ulignosus nymphs 12.2%, G. punctipes (Say) adults 19.2%, and 43.7% other Geocoris spp. nymphs,

and no G. bullatus (Say) adults were sampled (n=213).




60




From relatively low numbers at the start of the season, Geocoris numbers increased gradually, reached a peak of

0.43 per sample, then declined in number during September (Fig. 11).

The striped earwig, L. riparia, fluctuated widely in

abundance between fields composing 1.8-47.4% of beneficials sampled. Most of the L. riparia sampled were observed while parting the foliage in preparation for beat cloth placement. Labidura riparia numbers climbed rapidly from very low initial numbers to greatest numbers of 1.1 per sample at the season's end (Fig. 10). Mark-recapture analysis of absolute earwig population levels in 2 Alachua County peanut fields during late August and early September indicated maximum populations of 34,400-85,227 earwigs/ha (Travis 1977).

Nabids were relatively abundant only midway through the season and a decline in nabid numbers occurred in September (Fig. 11). In 1976 Tropicanibis capsiformis (Germar) and Reduviolis roseipennis (Reuter) composed 99 and 1%, respectively, of the total nabids collected for identification (n=100). Of 240 nabids sampled in 1978, 96% were T. capsiformis, 2.5% were R. roseipennis, and 1.5% were Pagusa fusca (Stein).

Adults of the insidious flower bug, Orius insidiosus (Say), reached peak abundance during mid-June and July,then declined sharply (Fig. 11). Patterns of abundance of O. insidiosus may be associated with peanut flowering since




61



pollen seems to be an important part of diet of both nymphs and adults (Diecke and Jarvis 1962). Also, tobacco thrips are most abundant before flowering and may serve as prey.

Ground beetle adults and larvae composed 3.2-9.5% of the predator complex. The most numerous species of ground beetle were the foliage dwelling Callieda decora (Fabricius). Callieda decora comprised 75 and 53% of the carabids sampled in 1977-1978 respectively, Peak abundance of C. decora larvae occurred near peak numbers of fall armyworm and corn earworm. Collurius pennsylvanicus (Linnaeus) adults composed

7.3 and 47% of the carabids collected in 1977 and 1978, respectively. Other carabids infrequently encountered were adults of Anisodactylus merula Germstacker, Selenophorus palliatus Fabricius, S. ellipticus Dejean and Teragonoderus intersectus Germar and larvae of Progaleritina spp. and Calosoma sayi Dejean.

Many of other predaceous arthropods occurred in numbers too low for assessment of their seasonal dynamics. None of these predators averaged more than 0.5 per sample on a given date during this 3 year study. Some of the predators that were observed in most fields in low numbers include: Doru taeniatum (Dohr) (Forficulidae), Spanogonicus albofasciatus (Reuter) (Miridae), Zelus cervicalis (Stal) (Reduviidae), Sinea spp. (Reduviide), Podisus maculiventrus (Say) (Pentatomidae), Chrysopa spp. larvae (Chrysopidae), Scymnus spp. adults (Coccinellidae) and Noxtoxus spp. adults (Anthicidae).




62




Classical predator-prey theories predict gross predator population density fluctuations similar to the host-population's gross variations (Watt 1968). Significant positive correlations demonstrate associations or similar patterns of variation between larvae and predaceous arthropods. The explanation for association may be chance, or indicative of density dependence phenomena.

Spiders were significantly correlated with foliage feeding larvae (FFL) twice, velvetbean caterpillar (VBC)

6 times, and fall armyworm (FAW) once (Table 4). For earwigs there were 6 significant associations involving FFL once and VBC 5 times. Nabids had the greatest total number of correlations. Nabids were correlated with FFL

4 times, VBC 11 times, and FAW once. Geocoris spp. showed few correlations; they were associated with VBC twice, FAW twice, and CEW twice. Ants were associated with VBC once, the fewest significant associations of all predator groupings. Orius insidiosus adults showed significant correlations with FFL twice, FAW 3 times, and CEW 3 times.

For further elucidation of association patterns a

refinement in sampling technique and statistical analysis is needed. Absolute samples or calibrated relative samples of pests and beneficials analyzed using multivariate analysis may prove useful in clarifying associations.

Some inferences about the relative importance of predaceous arthropods on north Florida peanuts can be made.




63



Ants were the most numerous predators sampled and probably one of the most important predators regulating pest populations. Ants have been frequently observed consuming lepidopterous eggs in Florida soybeans (Buschman et al. 1977, Nickerson et al. 1977). Lack of many significant correlations between larvae and ants is not surprising considering ants were one of the most under-sampled predators in this study. Some species of ants only forage at night (Whitcomb et al. 1972) and most ants are underground at any given time.

Because of the abundance of families represented spiders occupy a variety of feeding niches. Whitcomb (1974) stated

4 important roles of spiders as follows: (1) spiders prey on destructive insects; (2) spiders serve as food for predators; (3) spiders tend to be general feeders, and (4) spiders compete with insect predators for prey. Spiders have been reported as important egg predators in Florida soybeans (Buschman et al. 1977). The abundance of spiders in peanuts suggests they are important in effecting pest population dynamics.

Eggs and small larvae of noctuids are part of prey of Geocoris spp. However, Geocoris spp. consume a very broad array of prey (Crocker 1977). Menke and Greene (1976) reported large Gooeoris spp. populat ions exerted little population regulation of velvetbean caterpillar populations in north Florida soybeans. Consequently, Geocoris spp. were probably not major predators in north central Florida peanuts.





64




The habits of ground beetles are extremely varied

often within the same genus. Callieda decor was the only ground beetle sampled in sufficient numbers to be important in some fields. In 1977 C. decora was observed numerous times feeding on small to medium corn earworms. Calosoma sayi adults and larvae were numerous in pitfall traps in peanut fields with high VBC populations in 1976 (Travis unpubl.). Calosoma sayi consumes and reacts to noctuid pests of soybeans by taking progressively more prey items as they become available (Price and Shepard 1978). Calosoma sayi is one of the few potentially important predators of large larvae and pupae in peanuts.

Labidura riparia were important predators in most

fields during this study. Earwigs were especially uncommon in Field N in 1977; it is possible that application of parathion on 6 July followed by a 27 July application of monocrotophos may have greatly reduced the earwig population in this field. All stages of noctuids may be consumed by L. riparia (Schlinger et al. 1959, Hasse 1971, Neal 1974). In laboratory tests functional response of earwigs to noctuid larvae prey indicated that successful attacks increased

with higher host density (Price and Shepard 1978). That L. riparia numbers were associated with foliage feeding larvae was demonstrated by significant correlation coefficients and the gradual increase in earwig numbers during the season (Fig. 10). L. riparia is considered an important predator




(65



in Florida soybeans (Neal 1974, Buschman et al. 1977). Labidura riparia is probably one of the most important predators in peanuts in north central Florida.

T. capsiformis adults and nymphs were potentially

important predators of VBC larvae. The increase in nabid populations closely followed the increase in VBC larvae. Nabids were uncommon earlier in the 3 seasons when FAW and CEW were present. Nabids consume eggs and small larvae of noctuid pests.

0. insidiosus was not numerous during the season when defoliators were numerous. However, 0. insidiosus may have served to suppress early season outbreaks of some pests during June. During the increase in VBC numbers O. insidiosus were not common.






66








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SPATIAL DISTRIBUTIONS OF DEFOLIATING
LEPIDOPTEROUS LARVAE ON PEANUTS Introduction

Spatial distributions are a useful means of quantifying the dispersion of insects in a given habitat. Spatial distributions are useful in several ways: (1) to aid in determining the appropriate transformation for analysis of variance; (2) to develop sequential decision plans; and

(3) to develop sampling plans. Also, inferences about the biology of the insect e.g., dispersal patterns, can be made. Spatial distribution models are probability distributions that relate the frequency of occurrence of an event, depending on the mean of the measurements and in some cases on one or more parameters.

The most useful statistical distributions in entomological research have been the Poisson and negative binomial (Southwood 1978). The Poisson distribution describes a random distribution with variance equal to the mean. Most commonly in insect sampling the variance will be larger than the mean, indicating that the distribut i on is aggregated or clumped. The most useful distribution describing a clumped insect population has been the negative bionomial.





72




73




The versatility of this distribution arises from the fact that it may be derived from at least 5 different models (Waters and Henson 1959).

The objective of this study was to determine the spatial distribution of the major foliage feeding insect pests of peanuts in Florida.


Methods and Materials

Forty samples per week were taken by the ground-cloth shake method from 0.91 m of row from growers' fields of 'Florunner' peanuts, 1976-1978. Thus the field counts of foliage feeders were taken from different field sizes and population densities.

Insects sampled included velvetbean caterpillars, Anticarsia gemmatalis IIubner; fall armyworm Spodoptera

frugiperda (J. E. Smith); corn earworm, leliothis zea (Boddie); granulate cutworm Feltia subterranea (Fabricius); and Plusiinae loopers: Trichoplusia ni (Hubner), Pseudoplusia includens (Walker), and Argyrogramma verruca, (Fabricius). Mixed populations of loopers prohibited differentiation of these species in the field.

Data sets were arranged into discrete frequency classes and fitted to ma themat;ical distrihbutions utilizing a computer program developed by Gates and Ethridge (1972). Only those data sets with 4 or more frequency classes were analyzed and fitted to a distribution. The observed





74



frequency distribution for the following distributions: Poisson, Poisson-binomial, Poisson with zeroes, negative binomial, Neyman type A, and Thomas double Poisson.

The iterative solution technique of Bliss and Fisher

(1953) was used determining the parameter k of the negative binomial. Common k values were calculated by the iterative method (Formula 10) of Bliss and Owen (1958).


Results and Discussion

Data sets of counts of lepidopterous larvae fitted the negative binomial or Poisson with zeroes better than any other distribution (Table 5). Data sets obtained from counts of fall armyworm and velvetbean caterpillar fit the negative binomial significantly better than Poisson. The percent fit of data sets to the negative binomial for all larvae was relatively high--i.e. 82-90% while similar studies in soybeans by Shepard and Carner (1976) and in cotton (Kuehl and Fye 1972) showed lower fits of negative binomial for some of these same species. The Poisson distributions fit the data fewer instances, 41-70% in every case.

Values of common k for larvae were 3.93 for fall armyworm, 5.20 for corn earworm, 7.27 for velvetbean caterpillar,

2.51 for granulate cutworm, and 3.58 for loopers. Only the former 2 common k values significantly fit (P=0.05) a / test for homogeneity of k in the different samples.










The value of k may not be a constant for a population but often increases with the mean. However, regressions of I/k versus population means for individual species were not significant P=0.05. This indicates that k values and means were not related. Large variation in sample k values caused the lack of fit. Neither size or age classes of larvae were considered in fitting distributions. Grouping instars may have increased the k values by combining the different instar distributions.

When action economic thresholds for peanuts are revised sequential sampling plans may be developed using the formula presented by Waters (1955). The common k values determined for fall armyworm and corn earworm can be used for calculating decision lines. The formula for decision lines for populations described by the Poisson distribution will be adequate for the other species of lepidopterous larvae.





76










Table 5. Percentage fit of counts of foliage consuming lepidopterous larvae to the expected frequency distributions,
1976-1978.


Fall Corna Velvetbeana Rank armyworm % Fit earworm % Fit caterpillar

1 Neg. binomial 84 Poisson/zeroes 84b Neg. binomial
2 Neyman 73b Neg. binomial 82 Neyman
3 Poisson-bin. 69b Neyman 82b Poisson-bin.
4 Thomas 66b Poisson-bin. 77b Poisson/zeros
5 Poisson/zeros 65b Thomas 73b Thomas
6 Poisson 41d Poisson 61b Poisson


aNumber of observed frequency distributions equals 51 for FAW,
14 for IIeliothis spp., 39 for VBC, 33 For loopers, and 28 for
GCW
b,
/% fit not significantly different from the % fit of the negative binomial distribution at the 5% level

c/ fit significantly different from % fit of negative binomial at 5% level

d% fit significantly different from % fit of negative binomial
at 1% level





77











Table 5. -- Extended



Granulate
% Fit Loopersa % Fit cutworm % Fit

87 Poisson/zeros 94b Neg. binomial 90
80b Neg. binomial 88 Neyman 85b 77b Neyman 82b Thomas 85b 74b Thomas 79b Poisson/zeros 82b 61b Poisson-bin. 73b Poisson-bin. 75b 54c Poisson 70b Poisson 68b

















EFFECTS OF UNIFORM HAND DEFOLIATION OF
PEANUTS ON PLANT GROWTH


Introduction

Peanut (Arachis hypogaea L.) yields in the southeastern United States may be reduced by a complex of arthropod pests. Most of the insecticide applications in the southeastern peanut belt are made to control foliage feeding noctuid larvae (French 1973). Foliage feeding larvae reported capable of causing yield loss include corn earworm, Heliothis zea (Boddie), fall armyworm, Spodoptera frugiperda (J. E. Smith), and velvetbean caterpillar, Anticarsia gemmatalis (Hubner) (Bass and Arant 1973). In Florida, noctuid larvae may become numerous 10 weeks after planting and damaging levels of larvae may occur until harvest.

Information relating peanut foliage loss to yield

is variable for a given plant age and variety. Previous defoliation experiments have dealt with peanut varieties other than 'Florunner' (Enyi 1975, Williams et al. 1976, King et al. 1961) or have examined only the influence of defoliation of 'Florunner' on yields only (Greene and Gorbet 1973, Nickle 1977).

A mowing machine was used by Greene and Gorbet (1973) to remove the upper portions of peanut canopies to approximate 5 levels of defoliation of 'Florunner' peanuts in



78





79



Florida. Removal of an estimated 33% of leaf area reduced yields 5-44% except for a 2% yield increase at 81-90 days after planting. Yield reductions averaged for the 3 years of defoliation experiments at 58, 65, and 108 days after planting were 3.8, 13, 21.5, and 44% yield loss from 10-15, 20, 33, and 50% defoliation, respectively. At the 50% defoliation level some stems and pegging branches also were removed.

Nickle (1977) hand defoliated unirrigated 'Florunner' peanuts in Florida at 5 dates. Yield reductions averaged 2-6.8, 7.2-21.6, 16.8-41.2, and 20-51% from 25, 50, 75, and 100% defoliation respectively for the 2 defoliation experiments. Greatest yield reductions for both experiments resulted when defoliation occurred at 63 days after seedling emergence.

Few studies describe how defoliation affects peanut

canopy characteristics and plant growth. Boote et al. (1980) reported the effect of 75% hand defoliation of the upper 42% of canopy leaf area of unirrigated 'Early Bunch' peanuts. Measurements were made of light interception, specific leaf weights (SLW), leaf area index (LAI), apparent canopy carbon exchange, and photosynthetic uptake of 14CO2

4 days after defoliation. Effects of defoliation on peanut growth and yield are being quantified using a modeling approach (G. Wilkersonl). Simulation of peanut defoliation Ms. Gail Wilkerson, graduate assistant, Univ. of Florida.




80




will enable the experimental control of the many interacting factors (environment, insect populations, crop phenology) at will. Current peanut plant growth models (Duncan 1974, Young et al. 1979) lack components for coupling defoliation to plant growth. Objectives of the present study were to describe how defoliation affects canopy characteristics and plant growth.


Materials and Methods

Peanuts cv. 'Florunner' were hand planted in 3 blocks 42m X 22 rows 22-23 May 1978 at the University of Florida Agronomy Farm, Alachua County, Florida. The soil type was Arrendondo fine sand. Row spacing was 76.2 cm with plants spaced 13.8 cm apart in the row, which is within the range of plant population for maximum yield (Malagamba 1976). Weed control was achieved with preplant (.6 kg a.i./ha benfluralin and 2.3 kg a.i./ha vernolate) and cracking time (2.8 kg a.i./ha dinoseb and 2.4 kg a.i./ha 2,4-DEP) herbicides. Ethylene dibromide (253 ml/chisel/100m) was injected

5 days before planting for nematode control. Gypsum was applied by hand at 1700 kg/ha on 26 June. The fungicide chlorothalonil was applied at 0.8-1.1 kg a.i./ha starting on 22 June at 7-10 day intervals until 22 September.

Monocrotophos (1.9 kg a.i./ha) was applied on 29 June

for lesser cornstalk borer (Elasmopalpus lignosellus (Zeller)). Either methomyl (.6 kg a.i./ha), carbaryl (1.2 kg a.i./ha) or





81



acephate (1.1 kg a.i./ha) were used to kill foliage feeding noctuid larvae (corn earworm, velvetbean caterpillar, fall armyworm, and Plusiinae loopers) and were applied at 7-14 day intervals from 15 July until 22 September. Insecticides and chlorothalonil were tank mixed and applied with a pressurized backpack sprayer. On 24 August fensulfothionPCNB granules (40.3 kg a.i./ha and 13.4 kg a.i./ha, respectively) were broadcast by hand to slow the spread of white mold, Sclerotium rolfsii Sacc. infestation. Overhead irrigation was used to prevent extreme water stress. Pesticides and cultural practices used were designed to minimize pest damage and still be reasonably similar to typical grower practices.

Four levels of defoliation were obtained by removing

0, 1, 2, or 3 leaflets from all tetrafioliates with a petiole extension, corresponding to 0, 25, 50, and 75% defoliation, respectively. Fifty leaflets from 3 plots of each defoliation treatment were saved for leaf area determination with an automatic area meter and drying at 700 C.

Defoliation and check plots were selected for uniformity at 5 weeks after planting and assigned randomly to treatments. Defoliation plots were 1.1 m lengths of row with (1) at least 1.5 m between plots in the same row and (2) undefoliated adjacent border rows. Plots were defoliated at 25, 50, and 75% at 8, 11, 13, and 15 weeks after planting. At 17 weeks the only defoliation level was 75%. In addition,




82




there was (1) a treatment at 8 weeks of 75% defoliation plus removal of buds for 7 days and (2) a redefoliation treatment of 75% defoliation at 15 weeks of some plots 75% defoliated at 11 weeks.

At 2 week intervals, starting 2 weeks after a defoliation, until harvest at 19 weeks after planting, 3 samples of 75% defoliated plots of 11, 13, 15, and 17 weeks were removed. At 19 weeks after planting 4 plots of all treatments were harvested for yield. Similarly, undefoliated plots were removed at 8, 10, 11, 13, 15, 17, and 19 weeks. Four replicate samples of the 8th week defoliations also were removed at 10 weeks. One plant from each plot, not one of the plants bordering undefoliated plants in the row, was separated into roots, stems, leaves, pod shells, and kernels for dry weight determination. The remaining plants in the plots were dried and total plot weights were obtained by summing plant parts of a plot and remaining plants. Leaflets from undefoliated plots were separated into leaflets present at defoliation ("old" leaves) and intact leaves ("new" leaves) expanded since defoliation date. Leaf area and dry weights were measured from 50 "new" and "old" leaves. Single plant part percentages and total plot weight were used to calculate dry weights of plant parts per unit area.

The photosynthetically active radiation (PAR) intercepted by peanut canopies was measured 1-3 days after defoliation using a pyranometer (LI-200S)1 in conjunction with






83



1
a quantum-radiometer-photometer (LI-185) and pringing
1
integrator (LI-550) Photosynthetically active radiation measurements were taken 1-3 days after defoliation on days of clear skies between 900-1500 hours EST. A metal track 3 cm wide with 3 cm sides was inserted perpendicular to the row between plants. The pyranometer was pulled by its cord manually along the track at a timed constant rate for 1 minute. An ambient full sun reading above the canopy was recorded within 1-2 minutes of canopy reading.


Results and Discussion

The daily rainfall, irrigation, solar radiation,

maximum and minimum temperatures from planting until harvest are given in Appendix Table 12.

Percent light interception of peanut canopies under different levels of defoliation at different plant ages is given in T.ble 6. The LAI for intact canopies was

3.11, 4.52, 5.65, 6.09, 5.53 and 5.45 at 8, 11, 13, 15, 17, and 19 weeks after planting, respectively. Quadratic regressions for LAI and percent light interception of intact canopies and of canopies defoliated 27-75% at 8, 11, 13, 15, and 17 weeks after planting were calculated (Fig. 12). Two LAI--percent light interception coordinates taken at 6.5 and 9 weeks after planting used in the




1Lamba Instruments Corporation, Lincoln, NE.




84




intact canopy regression were taken from an adjacent peanut experiment (G. Wilkerson unpubl.).

Differences in canopy structure at a given LAI is a

probable explanation for the difference in regression equations of light interception--LAI for intact defoliated canopies. In general, most of the LAI data used to fit the defoliated canopy curve represent canopies with greater stem areas and ground cover. Ten of the 13 defoliated canopies had an LAI less than 3. Of these 10 canopies, 7 were from plots 11 or more weeks old. Stem growth is almost complete at 11 weeks and stems intercept 39% of ambient light when leaves are removed from full grown plants (Jones2 et al. unpubl.). By 11 weeks ground cover was 100%. The stem light interception plus the possibly more uniform spacing of leaves on plants exhibiting 100% ground cover compared to intact canopies with a LAI less than 3 probably caused the higher light interception readings of defoliated canopies at a given LAI.

To estimate the difference in crop and pod growth

rates of intact and 75% defoliated canopies at 11 and 13 weeks after planting, linear regression curves of dry weights versus plant age were calculated. Since more photosynthate is necessary for kernel development than other

plant parts, a result of the higher concentration of oil and protein in seeds than in other plant parts, an adjust2J. W. Jones, C. S. Barfield, K. J. Boote, G. II. Smerage, and J. Mangold. Photosynthetic recovery of peanuts to defoliation at various growth stages. MS in review.




85



ment was used. Average values of the correction factors developed by Hanson et al. (1961) and Penning de Vries (1974) for seeds--i.e. 1.88 X kernel weight were used.

The growth response of intact plants, 75% defoliation at 11 weeks, and 75% defoliation of plants at 13 weeks is illustrated in Fig. 13. Regression equations for crop and pod growth rates are presented in Table 7. The crop growth rate of intact canopies appeared to slow late in season. The decrease in growth rate was probably due to the few new leaves that are added and the photosynthetic rate of older peanut leaves decreases with age (Trachtenberg and McCloud 1976, Henning et al. 1979).

There was a greater relative reduction in pod and crop growth rate of plants defoliated at 13 weeks than at 11 weeks. For plants defoliated 75% at 11 weeks, crop and pod growth rates were 71.7 and 76.1%, respectively, that of the undefoliated. Seventy-five percent defoliation at 13 weeks reduced crop and pod growth rates by 65.3 and 57.1% that of the undefoliated plants. A plausible explanation for the larger reduction in growth rates of 13th week defoliated plants versus lth week defoliated plants may be related to the lower average LAI present of 13th week defoliated plants during the remainder of the growing season. Plants defoliated in week 11 added LAI.

Partitioning coefficients were calculated from the crop and pod growth rates. Partitioning refers to the division




86




of photosynthate between reproductive and vegetative plant parts. Previously pod partitioning coefficients of undefoliated 'Florunner' peanuts has been estimated at 73% by linear regression of dry weights (McGraw 1977) and 84.7% by the PENUTZ model (Duncan et al. 1978). The calculated pod partitioning factors for the undefoliated plots from 11-19 weeks and 13-19 weeks. 75% defoliation at 11 weeks, and 75% defoliation at 13 weeks were 75.1, 80.9, 70.7, and 92.5% respectively.

Specific leaf weights of defoliated plants significantly increased in some cases after defoliation as compared to undefoliated plants (Tables 8, 9). Most of the increase in SLW was attributed to the increase in "old" leaf SLW. Old leaves increased in SLW probably due to less shading. Decreases in SLW with shading for peanuts (An 1976) and other legumes such as alfalfa, Medicago sativa L. (Wolf and Blaser 1972) and soybean, Glycine max (L.) Merr., (Cooper and Qualls 1967) have been reported.

An increase in SLW may be related to increased photosynthetic rates. Bhagsari and Brown (1976) detected a significant positive correlation between SLW and photosynthesis in 1 of 3 experiments involving peanut genotypes. However, no correlation between SLW and net photosynthesis of peanut leaves were found by Pallas and Samish (1974).

Defoliation reduced yields at most levels and plant

ages, but significant differences from undefoliated peanuts




87




occurred only with 75% defoliation at 8 weeks plus removal of buds for 7 days, 75% defoliation at 11 weeks, and multiple 75% defoliations at 11 and 15 weeks (Table 10). Early pod fill ca. 68-day-old plants has previously been shown as the plant age most sensitive to defoliation (Nickle 1977). Consumption or damage to terminal buds appeared to be an important compounding effect to uniform canopy defoliation. The early instars of corn earworm feed selectively on leaf tissues of terminal buds (Morgan 1979). Sustained terminal bud damage may be an important aspect of defoliator damage by corn earworm and possibly fall armyworm especially during the vegetative growth stage of peanuts.

Seventy-five percent defoliation and 75% defoliation

plus removal of buds at 8 weeks reduced pod and stem weights at 10 weeks (Table 11). Decreases in stem weight of 'Dodoma' edible peanuts with defoliation have been reported previously (Enyi 1975). The weight of leaves grown 2 weeks after 50 and 75% defoliation also was significantly higher than undefoliated plants. Defoliated peanut plants compensated for defoliation by growing more leaves and reducing stem and pod growth.

Plants defoliated 75% at 11 weeks grew significantly

more leaves than undefoliated plants during the 2 week period following defoliation (Table 1.1). No detectable differences in leaf growth between defoliated and undefoliated plants were detected in other treatments or time periods after defoliation.




88












Table 6. Average percent light interception of intact and
defoliated 'Florunner' peanut canopies after
defoliation

Percent Percent light interception
defoliation Defoliation date (weeks after planting)

8 11 13 15 17 19

Intact 69.5 90.6 96.9 94.0 92.9 95.5
25 68.3 83.1 91.2 81.8 50 57.5 80.0 75.8 77.2
75 51.8 63.4 70.5 50.7 60.6
75+buds1 45.2

1Buds removed for 7 days.





89








0 000 0

=Cl L -d ( O L 0 o Po .
0




. O CCO O to co O 4- LO C O ) 0o(9 I I 0 U
4 I o1 11 i b.0 H-) OC OO O









a 0 0 0 a
ci k(d1 L~t O CO









o
w2 aO II II II II Ci












oT M M G O 00 0 N







O LO G 0 C r- + + .1'HO + + 0 LO
@ -a to 0 O 0000 C)













O bO a


0 II I O- 0 0
dC








a)a -Q I 0 0







O.H 0- I I


-400 O -J + O @ C1







0 UR LO LO O bCO (0 o I I )t







Tc 5II II 0




o 0 4- aa
ci 0 C O

0 U) H v- ) 0000










E --4A H H H -H O) 42d c H1 II O 11




90









Table 8. Specific leaf weight (SLW) of peanut leaves from
intact and defoliated 'Florunner' peanut canopies
in relation to weeks after planting.


Age at 75% SLW (mg/cm) defoliation Leaf weeks after planting
(weeks) type 11 13 15 17 19

control 3.83 3.83 3.86 4.03 4.12
11 new 3.85 4.19 4.62 4.66
old 4.12 4.20 4.63 4.76 avg. 4.02 4.26 4.63 4.72
13 new 3.09 4.78 4.51
old 4.20 5.00 4.91 avg. 4.06 4.96 4.80
15 new 4.01 4.12
old 4.15 4.90 avg. 4.10 4.80
17 new 4.39
old 4.51 avg. 4.49

LSD for new leaves, old leaves, and svg. leaves=0.39, 0.45, and
0.47, respectively, P=0.05.




Full Text

PAGE 1

SEASONAL ABUNDANCE OF DEFOLIATING LEPIDOPTEROUS LARVAE AND PREDACEOUS ARTHROPODS AND SIMULATED DEFOLIATOR DAMAGE TO PEANUTS By JOHN ROBERT MANGOLD A DISSERTATION PRESENTED TO UNIVERSITY N PARTIAL FULFILLMENT OF THE OF DOCTOR OF UNIVERSITY THE GRADUATE COUNCIL OF THE OF FLORIDA REQUIREMENTS FOR THE DEGREE PHILOSOPHY OF FLORIDA 1979

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ACKNOWLEDGEMENTS The author wishes to acknowledge his sincere appreciation to Dr. S. L. Poe, research advisor and chairman, for his patience and assistance throughout the course of this study. Special appreciation is extended to the supervisory committee, Drs. J. W. Jones, C. A. Musgrave, D. H. Habeck, and C. S. Barfield for advice and critical reviews of the dissertation The author wishes to express his gratitude to the Department of Entomology and Nematology and in particular to Stephanie Burgess, Gail Childs, Micky Ilartnett, Donna Labella, Mike Linker, Carol Lippicott, John O'Bannon, Randy Stoutt, and John Wood for help with field work. The author also wishes to thank Dr. Habeck for identif cation of lepidopterous larvae, Skip (Paul) Choate for identification of Caribidae, and Roger Hetzman for identifi cation of Geometridae.

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TABLE OF CONTENTS Page ACKNOWLEDGEMENTS ii LIST OF TABLES ^ LIST OF FIGURES • ABSTRACT '^iii INTRODUCTION 1 LITERATURE REVIEW 5 Foliage Consuming Lepidopterous Pests 5 Predaceous Arthropods Associated with Peanuts ... 9 Spatial Distributions of Arthropods 9 Effects of Defoliation on Plant Growth and yield. H SEASONAL DYNAMICS OF DEFOLIATING LEPIDOPTEROUS LARVAE IN NORTH CENTRAL FLORIDA PEANUTS 1976-1978 21 Introduction 21 Materials and Methods 22 Results and Discussion 23 SEASONAL DYNAMICS OF PREDACEOUS ARTHROPODS IN NORTH CENTRAL FLORIDA PEANUTS 1976-1978 56 Introduction 56 Materials and Methods 57 Results and Discussion 58 SPATIAL DISTRIBUTION OF DEFOLIATING LEPIDOPTEROUS LARVAE ON PEANUTS 72 Introduction 72 Materials and Methods 73 Results and Discussion 74 EFFECTS OF UNIFORM HAND DEFOLIATION OF PEANUTS ON PLANT GROWTH 78 Introduction 78 Materials and Methods Results and Discussion iii

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APPENDIX LITERATURE CITED BIOGRAPHICAL SKETCH

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LIST OF TABLES Table 1. Characteristics of peanut fields used in survey, Alachua County, Florida 1976-1978 30 2. Relative abundance of lepidopterous larvae associated with Alachua County, Florida, 'Florunner' peanuts 1976-1978 31 3. Relative abundance of predaceous arthropods associated with Alachua County, Florida, •Florunner' peanuts 1976-1978 66 4. Correlation coefficients between lepidopterous foliage feeding larvae and predaceous arthropods on Alachua County 'Florunner' peanuts 67 5. Percentage fit of counts of foliage consuming lepidopterous larvae to expected frequency distributions, 1976-1978 76 6. Average percent light interception of intact and defoliated 'Florunner' peanut canopies after defoliation 88 7. Regression equations of pod and crop weights of intact and defoliated 'Florunner' peanut canopies ^9 8. Specific leaf weight (SLW) of peanut leaves from intact and defoliated 'Florunner' peanut canopies in relation to weeks after planting 90 9. Effect of defoliation of 8 week-old 'Florunner' peanut plants on plant parts, 2 weeks posttreatment 91 10. Effect of defoliation of 'Florunner' peanut plants on plant parts at 19 weeks 92 11. Dry weight of leaves from intact and defoliated 'Florunner' peanut plants 2 weeks after defoliation 93 12. Solar radiation, temperature, rainfall and irrigation during growing season, 1978 98 V

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LIST OF FIGURES Figure Page 1. Location of Alachua County Florida, peanut fields sampled in survey of peanut arthropods, 1976-1978 33 2. Mean' numbers of FAW CEW and VBC larvae sampled from Alachua County, Florida, peanuts 1976-1978. Breaks in lines indicate dates of insecticide application 3. Mean numbers of FAW larvae sampled from Alachua County, Florida, 'Florunner' peanuts, 1976-1978 4. Mean numbers of CEW larvae sampled from Alachua County, Florida, Florunner peanuts, 1976-1978 45 5. Mean numbers of VBC larvae sampled from Alachua County, Florida, Florunner peanuts, 1976-1978. ". 47 6. Mean numbers of VBC, FAW. and CEW larvae sampled from various age of Alachua County, Florida, 'Florunner' peanuts, 1976-1978 7. Mean numbers of Plusiinae looper larvae sampled from Alachua County, Florida, 'Florunner' peanuts, 1976-1978 8. Mean numbers of GCW larvae sampled from Alachua County, Florida, 'Florunner' peanuts, 1976-1978. ... 53 9. Mean numbers of BAW larvae sampled from Alachua County, Florida, 'Florunner' peanuts, 1976-1978. ... 55 10. Mean numbers of ants, spiders, and L. riparia sampled from Alachua County, Florida, 'Florunner' peanuts, 1976-1978 69 11. Mean numbers of Geo cor is spp., nabids, and 0. insidiosus adults sampled from Alachua County, Florida, 'Florunner' peanuts, 1976-1978 71 vi

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Fi gure Page 12. Quadratic regression of percent light interception to LAI of defoliated and intact peanut canopies, ** significant at 'v =0.01 level, and significant at rT=0.05 level 95 13. Dry matter accumulation in peanut plant parts in relation to weeks after defoliation. Pod weight is adjusted by factor of 1.88 X kernel weight 97 vii

PAGE 8

Abstract of Dissertation Presented to the Graduate Council of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy SEASONAL ABUNDANCE OF DEFOLIATING LEPIDOPTEROUS LARVAE AND PREDACEOUS ARTHROPODS AND SIMULATED DEFOLIATION DAMAGE TO PEANUTS By John Robert Mangold December, 1979 Chairman: Sidney L. Poe Major Department: Entomology and Nematology A survey of lepidopterous larvae on north central Florida peanuts detected 27 species during 1976-1978. The most abundant larvae were velvetbean caterpillar, Ant icarsia gemmatalis (Hubner), fall armyworm, Spodoptera f rugiperda (J. E. Smith), corn earworm, Heliothis zea (Boddie), Plusiinae loopers, granulate cutworm, Felt ia subterranea (Fabricius) and beet armyworm Spodoptera exigua (Hubner). Only the former 3 species of larvae reached damaging levels. Fall armyworm larvae were most abundant during mid-July to early August when peanuts were 12-17 weeks old. Corn earworm larvae were most numerous in mid-July when peanuts were ca. 12 weeks old. During August through early October velvetbean caterpillar larvae were most abundant on peanuts 15-17 weeks old. The most abundant and important predators surveyed in peanuts were ants, spiders, Labidura r ipar ia (Pallas), viii

PAGE 9

Geocoris spp. nabids, Orius insidiosus and ground beetles. Ants were abundant and probably important predators throughout the season. Spiders were common predators for the entire season. Labidura riparia numbers increased rapidly during the season to greatest numbers at the season's end. Geocoris spp. and nabids were abundant from mid-August to September then declined in number late in the season. Peak abundance of 0. insidiosus occurred during mid-June and early July, then declined sharply. Correlation coefficients between predators and foliage feeding larvae indicated nabid abundance was closely associated with velvetbean caterpillar numbers. Spiders, L. riparia Geocoris spp. and 0. insidiosus were also associated with larval numbers. The spatial distributions of fall armyworm, corn earworm, velvetbean caterpillar, Plusiinae loopers, and granulate cutworm were fit to 6 frequency distribution models. The common k values calculated for the 5 species were 3.93, 5.20, 7.27, 2.57, and 3.58 respectively. Only the first 2 common k 2 values significantly fit (P==0.05) a test for homogenity of k. Uniform hand defoliation of peanut canopies at 4 levels reduced yield of peanuts. Increases in specific leaf weight and decreases in light interception of defoliated canopies were recorded. Quadratic regressions of light interception as a function of leaf area index were calculated for defoliatai and intact canopies. Plants defoliated 75% at 8 and 11 weeks after planting compensated for defoliation by growing ix

PAGE 10

significantly more leaves than undef oliated plants. Plants defoliated 75% at 8 weeks also decreased stem growth. Defoliation also reduced crop and pod growth rates of defoliated plants compared to undefoliated plants. X

PAGE 11

INTRODUCTION The increasing world population has focused our attention on high protein food plants among which is Arachis hypogea L., the groundnut or peanut. Leading producers of peanuts by acreage are: India 35%, China 15%, United States 8%, Nigeria 8%, and Senegal 7% (Janick et al 1974). Approximately 650,000 ha of peanuts are produced annually in the United States. Peanuts rank ninth in acreage among major field crops and second in dollar value per acre in the United States (McGill et al 1974). The distribution of peanut acreage allotments in the United States is: Georgia 33%, Texas 23%, Alabama 14%, North Carolina 11%, Oklahoma 9%, Virginia 7%, Florida 4%, and South Carolina 1% (McGill et al. 1974). Peanuts are one of many crops in Florida's diversified agriculture. The Florida peanut acreage is ca. 22,270 ha of which 3,080 ha are in the state's north central peanut growing belt centered in Alachua, Levy, and Marion Counties (USDA 1977). Most insecticide applications on peanuts in the southeastern United States are made to control foliage consuming lepidopterous larvae (French 1973). Pilot pest management programs have demonstrated that insecticide usage can be 1

PAGE 12

2 substantially reduced with weekly population assessment and economic thresholds as a guideline for insecticide application (French 1975), The economic thresholds currently in use are based on limited data from defoliation experiments, larval consumption data, and principally on experience. Among the first steps toward the implementation of a pest management program are the determination of the insect pest species present in peanut fields and the evaluation of their effect upon the crop. In the United States the peanut pest complex varies with locality necessitating regional surveys. A knowledge of the regular, occasional, and potential pests in a particular area is necessary before steps can be taken to control them with timely usage of insecticide The seasonal dynamics of defoliating 1 epidopterous insects on peanuts in Florida has not been documented. Seasonal occurrence information for populations described in the literature from other states is based primarily on experience and not on long term studies. Data relating plant age to numbers of foliage feeding larvae have not been published, but are necessary for determining which plant ages should be critically studied in relation to defoliation. Foliage consuming larvae considered important in the southeastern United States include fall armyworm, Spodoptera f rugiperda (J. E. Smith), corn earworm, Hel iothis zea Boddie, velvetbean caterpillar, Anticarsia gemmatalis Hubner, granulate cutworm. Felt i. -3 subterranea (Fabricius), and beet armyworm, Spodoptera exigua (Ilubner) (Bass and Arant 1973).

PAGE 13

3 The use of natural control agents such as predators and parasites is ideally maximized in a pest management program. The parasite complex of lepidopterous larvae on Florida peanuts has previously been discussed (Nickle 1977) however, no description of the predaceous arthropod complex on peanuts in the southeastern United States has been reported. Any understanding of the biotic potential of both major and minor pests is impossible without an analysis of the predator complex in the crop. Better quantification of the relationship of defoliation to yield loss is needed to further define defoliation levels at which treatments are needed. A systems approach to peanut plant growth and development as affected by defoliation is being pursued to develop models that can realistically simulate the dynamic nature of insect defoliation and plant growth (Barfield and Jones 1979). Most previous defoliation experiments have emphasized defoliation effects on final yields, but ignored how defoliation caused the observed effect. Confounding environmental effects such as drought stress and the presence of other pests such as Cercospora leafspot have often made defoliation experiments less meaningful The objectives of the research reported here were to: 1. describe the seasonal occurrence of foliage consuming lepidopterous larvae on peanuts in north central Florida 2. determine the seasonal occurrence of predaceous arthropods in north central Florida peanuts

PAGE 14

4 3. determine the spatial feeding lepidopterous 4. examine the effect of damage on peanuts usi distribution of foliage larvae on Florida peanuts simulated defoliator g plant growth analysis

PAGE 15

LITERATURE REVIEW Foliage Consuming Lepidopterous Pests The arthropod fauna associated with peanuts in the United States is composed of endemic and introduced species that have adapted secondarily to this plant of South American origin. Thus, as a rule, arthropods infesting peanuts in North America are not specialized feeders, and their relative importance as peanut pests often is in inverse correlation to the availability of alternate preferred hosts. The peanut plant is damaged by a variety of arthropod pests in the United States. In the southeastern peanut belt most insecticide applications are made to control foliage feeding lepidopterous larvae (French 1973). Typically insecticides are applied 0-4 times per field to kill foliage feeding larvae. Foliage feeding larvae of major economic significance in the Southeast include fall armyworm, Spodoptera f rugiperda (J. E. Smith), corn earworm, Heliothis zea (Boddie), velvetbean caterpillar, Anticarsia gemmatalis (Hubner), and granulate cutworm, Feltia subterranea (Fabricius) Other arthropods of major economic importance in Florida include lesser cornstalk borer, Elasmopalpus lignosellus (Zeller) and spider mites.

PAGE 16

6 The fall armyworm is a periodic defoliator of peanuts in the southeast. Some feeding damage occurs every year and frequently sufficient number of larvae are present to completely defoliate plants in outbreak years (Bass and Arant 1973). Consequently, severe damage to peanuts in southeastern Alabama and southwestern Georgia has been reported (Arant 1948a). In Oklahoma, fall armyworm was reported numerous in some areas on peanuts during October, but damaging populations were not common in 1972-1974 (Wall and Berberet 1975). The corn earworm usually causes light to moderate damage. Occasionally severe infestations occur and complete defoliation of plants occurs (Bass and Arant 1973). In a 2 year study in Georgia, Leuck et al (1967) found indices of foliage ragging by corn earworm damage were negatively correlated with yield. Morgan (1979) reported corn earworms were most damaging during early August in Georgia. Wall and Berberet (1975) found corn earworm was one of the 2 most common foliage feeders collected in Oklahoma. The corn earworm is the most common insect defoliator on peanuts in the West Cross Timbers area of Texas although populations usually are not economically damaging (Sears and Smith 1975). The velvetbean caterpillar also causes damage to peanuts every year in Alabama, Florida, and Georgia (Bass and Arant 1973). Damaging populations of velvetbean caterpillars are not common in Oklahoma although larvae may become numerous in October (Wall and Berberet 1975). Velvetbean

PAGE 17

7 caterpillar is one of the few peanut defoliators that have been experimentally proven to significantly reduce yields. English (1946) applied insecticides for velvetbean caterpillar populations in Alabama and reported 9-65% yield reductions in untreated plots. Arant (1948b) demonstrated that velvetbean caterpillar defoliation caused 20-43% yield losses from untreated Alabama peanuts. The granulate cutworm damages peanuts by feeding on foliage and underground parts. When infestations are severe, portions of leaves and stems may bo cut from the plants. In Georgia damaging infestations may occur from late June until early August, but are most frequent about mid July when as many as 11 larvae per row foot may be present (Morgan and French 1971). Three generations of granulate cutworm on peanuts have been recorded from Georgia (Bass and Johnson 1978). Cutworm populations peak in late June, late July, and again in late August: the last generation is usually the most noticeable and damaging. The beet armyworm, Spodoptera exigua (Hubner) is a minor foliage feeding pest that infrequently causes damage. A few instances of serious defoliation have been reported (Bass and Arant 1973). Larvae of the rednecked peanutworm, Stegasta bosqueel 1 a (Chambers) may cause minor damage (Bass and Arant 1973). Feeding is confined to unopened leaves and the meristematic region of buds and thus larvae may retard terminal growth (Arthur et al. 1959). The rednecked peanutworm is the most

PAGE 18

8 common insect pest of peanuts in Oklahoma (Wall and Berberet 1979). Walton and Matlock (1959) obtained significantly higher yields through use of chemical controls for this pest in Oklahoma, but Arthur et al (1959) and Bissell (1941) reported that control of this pest did not increase yields in Alabama and Georgia, respectively. A number of other foliage feeding larvae have been associated with peanuts. These potentially injurious insects include: the tobacco budworm, Hel iothis virescens (Fabricius); yellowstriped armyworm, Spodoptera ornithogall i (Guenee); the saltmarsh caterpillar. Est igmene acrea (Drury); the yellow wollybear, Pi acris i a virginica (Fabricius); green clovorworm, Plathypena s cabra (Fabricius); cabbage looper, Trichoplusia n j (Hubner); soybean looper, Pseudoplusia includens (Walker); cotton square borer, Strymon mel inus (Hubner); Platynota nigrocerri na Walsingham; and Argyrogramma verucca (Fabricius) (Kimball 1965, Canderday and Arant 1966, Tietz 1972, Wall and Berberet 1975, Smith and Jackson 1976, Martin 1976). There is a paucity of published information on the seasonal abundance of foliage feeding larvae. Sears and Smith (1975) developed a partial monthly life table for corn earworm on Texas peanuts. Greatest larva] numbers occurred during July. Weekly averages of foliage feeding larvae in 1972 for 4 Georgia peanut fields were reported by French (1974). Granulate cutworms, corn earworms and fall armyworms comprised 77% of the larvae sampled, but seasonal fluctuations for individual species were not given.

PAGE 19

9 Predaceous Arthropods Associated with Peanuts Knowledge of the seasonal and relative abundance of predaceous arthropods is helpful in defining their role in regulating pests of peanuts. With the exception of a report of striped earwigs, Labidura riparis (Pallas) collected in pitfall traps in Florida peanuts (Travis 1977), there have been no studies of seasonal incidence or relative abundance of predators in peanuts. Martin (1976) found Coleomegilla maculata (De Geer) and Geocoris punctipes (Say) the most numerous predators in small peanut plots in north Florida; and spiders were present in low densities. Predaceous insects most commonly found in Texas peanut fields are lady bugs, assassin bugs, lace-wings, ground beetles, predaceous stink bugs, Geocoris spp., Nabis Orius and praying mantids (Smith and Hoelscher 1975). Spiders were one of the more numerous predators sampled in a study of the effect of insecticide placement on nontarget organisms in Texas peanuts in 1972-1973 (Smith and Jackson 1976). Spatial Distributions of Arthropods The method of sampling for foliage feeding lepidoptera larvae has been manual shaking of plant branches onto a ground cloth similar to the method of sampling soybeans developed by Boyer and Dumas (1963). The foliage shaking sample method has been used extensively in Georgia, Florida, Alabama, and Texas and economic thresholds are based on sampling results obtained with it. In North Carolina a standard sweep net is recommended for population estimation (Stinner et al 1979).

PAGE 20

10 Recent emphasis on accurate sampling procedures for insects in peanuts has revealed the need for better definition of the spatial distribution of these insects. Also, knowledge of spatial patterns provides insight into the biology of the species in question. Data on the spatial distribution of insects is necessary before development of sequential sampling schemes may be effected (Waters 1955). Spatial distribution models are probability distributions that relate the frequency of occurrence of an event, depending on the mean of the measurements and in some cases on one or more parameters. The most useful statistical distributions in entomological research have been the Poisson and negative binomial (Southwood 1978). The Poisson distribution describes a random distribution with variance equal to the mean. In insect sampling the variance most commonly will be larger than the mean, indicating that the distribution is aggregated or clumped. The most useful distribution describing a clumped insect population has been the negative binomial. The versatility of this distribution arises from the fact that it may arise from at least 5 different models (Waters and Henson 1959). The probabilities of a Poisson distribution are given by /V X P = g ^ /-^ x = 0, 1, 2, X X'! where P is the expected proportion in the xth class and X = 0 1 2 is the value of a discrete random variable.

PAGE 21

11 The mean and variance of the distribution are equal toyU. The usual procedure is to make a number of observations and The negative binomial is defined by 2 parameters, the mean and a positive exponent k. The distribution is generally expressed by the expansion of With increasing randomness, the variance of the distribution approaches the mean and the Poisson more accurately describes the distribution. Effects of Defoliation on Peanut Plant Growth and Yield Typically, peanuts in Florida are planted from early April to late May; in exceptional years spring droughts delay some planting until June. 'Florunner' released in 1969, is the most widely grown peanut cultivar in the United States. Over 80% of the peanuts grown in Florida are 'Florunner'. Peanuts exhibit an indeterminate growth pattern. The plant growth of 'Florunner' is prostrate with the typical sequential branching pattern of Virginia type varieties — i.e. alternate pairs of reproductive and vegetative nodes on laterals and no reproductive nodes on main stems. 'Florunner' peanuts grown under normal conditions in Florida begin flowering at ca. 30 days after planting; peak the mean of these, x, provides an estimate of ytLand (q-p) ^ where k> 0 p= and q= 1 + p. The expansion of the probability is given by X = 0,1,2

PAGE 22

12 flowering occurs at 60 days. After 80 days flowers are no longer present (McCloud 1974, McGraw 1977). The seasonal flowering pattern has a frequency curve similar to a normal distribution. Pegs begin to appear ca. 7-14 days after flowering. Generally only 15-307o of the flowers produce mature pods (Smith 1954). Early pegs generally produce a higher proportion of fruit than pegs initiated later. Usually by 56 days after planting the first pegs begin to swell into pods. Pod number per plant increases steadily until ca. 84 days at which time the pod load stabilizes. By day 70, seeds begin filling. Pod formation is completed soon after the full pod load is established and growth thereafter is in the seed (Duncan et al 1978). The pegs and pods which fail to mature remain attached to the plant and are not eliminated by abscission (Smith 1954). McGraw (1977) used plant growth analysis to describe 'Florunner' growth as follows: Plant growth followed a sigmoid curve. The first 7 weeks of vegetative growth was geometric. All assimilates were used for accumulation of dry matter into vegetative parts. The largest component in terms of dry matter during this phase was the leaf component. There was a linear growth phase which extended from week 7 to week 16. At 10 weeks plant development shifted from vegetative to reproductive growth and the rate of dry matter production began to slow since more photosynthate production was required for seed production than vegetative matter. Dry matter accumulation in the stem and leaf component ceased at about 84 days. The pods filled at a linear rate until maximum dry weight was reached at day 133.

PAGE 23

13 Duncan et al. (1978) calculated the crop growth rate of 'Florunner' from the same data used by McGraw. Linear regression of crop dry weights from canopy closure at 55 days until seed growth became significant at 70 days deter2 mined that the crop growth rate was 21.2g/m /day. This was assumed to be the period of maximum crop growth rate. Partitioning was used by Duncan et al. (1978) to refer to the division of daily assimilate between reproductive and vegetative plant parts. The partitioning factor may be calculated by comparing the fruit and vegetative growth rates. A correction is made for the fruit growth rate to account for the additional energy expenditure of seed production. Correction factors developed by Hanson et al. (1961) and Penning de Vries (1974) are used to compensate for the higher concentration of oils and proteins in seeds. Duncan et al (1978) estimated partitioning by 2 methods for 'Florunner'. From comparison of crop and corrected fruit growth rates the reproductive partitioning factor was calculated as 84.7%. The value for the reproductive partitioning factor estimated from simulations of the PENUTZ model was 72% (Duncan et al. 1978). Two useful terms often used to describe plant canopies are leaf area index (LAI) and percent ground cover. Percent ground cover is the percent of soil surface that is covered by the crop canopy. The LAI is defined as leaf area per unit of ground area and does not indicate directly the amount of solar radiation intercepted by the canopy. Larval

PAGE 24

14 consumption rates of leaf tissue can, however, be easily coupled to LAI. Measurement of percent light interception and LAI of canopies are both needed for describing the structure of defoliated and intact canopies. For example, ^ Rudd et al. (1979) used the light interception — LAI relationship of soybean. Glycine max L. (Merr.) determined by Shibles and Weber (1965) to model soybean insect defoliation in a dynamic model of soybean growth and yield. McGraw (1977) found that ground cover of peanuts increased geometrically from 10% at 3 weeks to 100% at 8 weeks after planting and remained 100% until harvest. The LAI increased from 0.11 at 3 weeks to 1.5 at 7 weeks. At 8 and 10 weeks the LAI had reached 3.6 and 5.6, respc;ct ively After 10 weeks the LAI maintained an average of 5.6 for 5 weeks until Cercospora leaf spot partially defoliated the canopy There have been several reported defoliation experiments of various varieties of peanuts with very inconsistent yield reductions (King et al. 1961, Greene and Gorbet 1973, Enyi 1975, Williams et al 1976, Campbell unpubl"!", Nickle 1977). Results generally demonstrate that defoliation at early podfill, 8-12 weeks after planting, causes the most serious yield losses. King et al (1961) simulated defoliator damage by mechanical removal of leaf canopy from the top 1/3 2/3 's ^Dr. W. V. Campbell, professor of entomology, North Carolina State University, Raleigh.

PAGE 25

15 of irrigated and dryland peanuts in Texas. Seventy-five percent defoliation of 56-day-old plants and 50% defoliation of 75-day-old plants did not affect yields of irrigated peanuts. Thirty-three percent defoliation did not significantly reduce yields of 53and 94-day-old plants, but higher defoliation levels did reduce yield of dryland peanuts A mowing machine was used by Greene and Gorbet (1973) in a 3 year study to approximate 5 levels of defoliation of 'Florunner' peanuts in Florida. Removal of ca. 33% of leaf area reduced yields at most growth stages; yield was reduced more when defoliation was delayed. Yield losses ranged from 1.8-7.4%, 3.7-32%, 8.6-44% and 34-63% for defoliation levels of 10-15, 20, 33, and 50%, respectively. Some reproductive branches and pegs were removed at the 507o defoliation level. Enyi (1975) hand defoliated 'Dodoma' edible peanuts at 2 week intervals at 3 levels in Tanzania. Defoliation levels of 50 and 100% reduced pod and stem weight, and kernel size. Greatest yield losses occurred to plants defoliated ca. 1 week after early podding stage. It appeared that defoliation reduced pod number by slowing stem growth which resulted in a reduction in number of flowering nodes. Williams ot al. ( 1976) det:ermined growth rates of plant parts of 'Makulu Red' peanuts in Rhodesia. Defoliation levels of 50 and 75% were achieved by removal of 2-3 leaflets per tetraf foliate. Compared to the untreated check, defoliation

PAGE 26

16 decrcrsed cro]) growth rate^ 2 weeks after defoliation by 17-42%. Stem and pod growth rates were also decreased by defoliation. Campbell (unpubl.) used hand shears to clip leaves from unirrigated peanuts in North Carolina. Yield reductions started with 50% defoliation on 15 July and 15 September, and 20% defoliation on 1 September, and 10% defoliation on 1 and 15 August. Unirrigated 'Florunner' peanuts were hand defoliated at 5 levels at 2 locations in north central Florida (Nickle 1977). Yield reductions in both plots were most severe at 63 days after cracking. Yield reductions averaged 2-6.8, 7.2-21.6, 16.8-41.2, and 20-51% from 25, 50, 75, and 100% defoliation, respectively for the 2 defoliation experiments. Peanut quality was also reduced by some defoliation treatments Too often researchers have studied the effect of defoliation only in terms of the final harvest. Growth analysis is a useful tool in the quantitative analysis of plant growth. Generally 2 assessments are required to carry out a simple growth analysis of plants with a closed canopy-i.e., dry weights of plant material per unit area of ground and LAI of the canopy (Radford 1967). Knowledge of the time and rate of dry matter accumulation is vital to understanding the physiology of any crop and is particularly amenable to studying the effect of defoliation.

PAGE 27

17 Previous defoliation studies have examined only the effect of defoliation on final yield or limited growth rate changes caused by defoliation. One of the few papers reporting canopy characters and photosynthesis of defoliated peanuts was that of Boote et al (1980). Defoliation of 75% of the upper 42% of the canopy leaf area of unirrigated •Early Bunch' peanuts corresponded to 25% of the total leaf area and reduced light interception from 95.6 to 74%. Canopy carbon exchange rate was reduced 35% from 20.2 mg o ? 14 COg/dm /h to 13.1 mg C02/dm7h and uptake of was reduced by 30%. Nickle (1977) questioned the relevancy of manual excision of peanut leaflets in establishing crop damageyield relationships, manual leaf removal was thought to be more stressful than larval defoliation. However, Thomas et al. (1979) demonstrated good agreement in yield losses between manual soybean leaflet removal and defoliation by caged cabbage looper, T. ni Removal of a fixed proportion of leaflets per tetrafioliate throughout the canopy has a further disadvantage in that it may not realistically simulate the effect of insect defoliation in terms of canopy damage site. The early instars of soybean looper on soybeans are reported to feed selectively on low-fiber containing leaf tissues of terminal leaves. The later instar larvae feed on non-terminal leaves (Kogan and Cope 1974). Similar observations of corn earworm larval damage to peanuts were reported by Huffman

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18 (1974) and Morgan (1979). The last 2 instars of noctuid larvae consume 80-91% of the total consumed foliage (Snow and Callahan 1968, Nickle 1977), Most researchers have assumed terminal bud damage is minor compared to the much greater potential loss of older foliage. Surveys of foliage feeding larvae on peanuts in 1976 indicated that peanuts 11-19 weeks old were most often attacked by defoliators (Mangold et al 1977). Terminal damage at this time is probably not of major significance since the majority of leaf matter is present. Sustained terminal bud damage to younger plants during the geometric vegetative growth stage may be an important aspect of defoliator damage by corn earworm and possibly fall armyworm A systems approach to the effect of defoliation on peanut growth and yield is being pursued (Barfield and Jones 1979). There are currently 3 peanut plant models. Two of the models lack appropriate mechanisms for coupling defoliation to peanut growth and development (Duncan 1974, Young et al. 1979). The third model, by Smith and Kostka (1975) is based on yield loss and larval consumption rates and is not general enough for studying the dynamics of insect defoliation on plant growth. Based on limited dcT-foliation oxperiments, larval consumption data, and principally on experience, an economic threshold of 4 or more foliage feeding larvae per row foot was used in a pilot pest management program in Georgia in

PAGE 29

19 1972-1974 (French 1975). In 1974 the Georgia pilot program reduced applications from an average of 2 per field for defoliators to an average of 0.05 per field in the program's 114 fields. Sampling 7.6 m of row for defoliators by shaking the branches and the empirical threshold were responsible for the reduction in insecticide usage (French 1973). In 1975 the Tri-States Pest Management Project was initiated on corn, soybeans, and peanuts in Georgia, Alabama, and Florida. Shake cloths were used to sample 0.91 m sections of row for defoliators. An action threshold of 4 larvae per row foot was used before early August but later increased to 6 larvae per row foot after early August (Linker and Johnson 1978). In Texas, field observations and limited research data indicate 3-5 and 6-8 medium to large larvae per row foot can be tolerated before yield losses will occur on dryland and irrigated Spanish peanuts, respectively (Hoelscher 1977). Economic thresholds for defoliators on peanuts should be revised. The concept of economic threshold is very useful in the primitive state of the art. The economic threshold refers to the pest population density at which active control measures should be initiated to prevent the pest from reaching the economic injury level. The economic injury level is the lowest number of insects that will cause economic damage. However, there are many factors that ideally should determine an economic threshold. Beneficial insects, pest pathogens, plant growth stage, interacting plant pathogens,

PAGE 30

20 market prices, weather conditions, farming practices, economics of crop production, pest species, etc., influence the economic threshold. Economic thresholds are useful in providing a guideline to the farmer as to whether it is economical to control a pest Defoliation studies indicate that plant age greatly influences the amount of defoliation that can be tolerated without yield loss. The static nature of current action thresholds does not reflect the dynamics of the impact of defoliation on crop yield. Also, studies on larval consumption rates of peanut leaves demonstrate major differences in relative amounts of foliage consumed among defoliators (Snow and Callahan 1968, Nickle 1977, Huffman and Smith 1979). Future action thresholds should consider the balance of defoliator species involved at the time.

PAGE 31

SEASONAL DYNAMICS OF DEFOLIATING LEPIDOPTEROUS LARVAE IN NORTH CENT-RAL FLORIDA PEANUTS 1976-1978 Introduct ion In the southeastern United States most insecticide applications on peanuts have historically been made to control foliage consuming lepidopterous larvae (French 1973). Foliage feeding larvae reported reducing yields in the southeastern United States include fall armyworm, Spodoptera f rugiperda (J. E. Smith); corn earworm, Heliothis zea (Boddie); velvetbean caterpillar, Anticarsia gemmatalis (Hubner) ; and granulate cutworm, Feltia sub terranea (F. ) (Bass and Arant 1973). Practically no information is published on the seasonal occurrence of foliage consuming lepidopterous larvae on peanuts. Sears and Smith (1975) developed a monthly life table for corn earworm on Texas peanuts. Weekly averages of foliage feeding larvae for 4 Georgia peanut fields in 1972 were reported by French (1973), however; seasonal fluctuations of individual pest species were not given. The seasonal occurrence of foliage feeding lepidopterous larvae on peanuts in north central Florida was studied in 1976-1978 and the results are reported here. 21

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22 Matei'ials and Methods A total of 14 Alachua County, Florida, growers' fields planted to 'Florunner' peanuts were surveyed during 1976-1978 for relative densities of lepidopterous larvae (Table 1). Samples were taken at weekly intervals starting on 6 July, 15 June, and 23 June in 1976, 1977, and 1978, respectively, and continued until harvest. A total of forty 0.91 m of row samples were taken at each sample date by the ground cloth method Samples were taken by folding back the branches and gently placing a ground cloth 0.91X0.91 m against plant bases of one side of the row. The peanut canopy was beaten downward vigorously with forearm and hands 6 to 8 times over the cloth to dislodge arthropods. Arthropods that were observed either under the branches while inserting the ground cloth or on the ground cloth were identified, counted, and recorded In 1976-1977 samples were taken throughout each field in a manner similar to that used by commercial scouts. All areas of the field were sampled in a random manner with not more than 10% of the samples within ca. 20 m of any field edge. In 1978 samples were taken along the transects of an X-shaped pattern which was aligned along the diagonals of the field. Twenty samples per transect were taken every tenth row in Field M and every thirteenth row in Field N. Each week sampling began on a different row.

PAGE 33

23 The fields surveyed in this study were all in Alachua County in the vicinity of Archer, Florida (Fig. 1) on the southern edge of the southeast peanut belt. Approximately 3,080 ha or 14% of Florida's peanut acreage is in north central Florida. Vegetation surrounding the study sites was mainly woods and pasture with limited acreages of field corn and rarely soybeans. Some of the fields surveyed were adjacent. The adjacent fields sampled were: (1) C and D; K and L; and B, I, and J. Also Field E was located less than 1 km from I and J. Results and Discussion The following 27 species of lepidopterous larvae were associated with Alachua County peanuts: Arctiidae: Dia crisia virginica (Fabricius) and Estigmene acrea (Drury) ; Gelechiidae: Stegasta bosqueela ; Geometridae: Anavitrinella pampinaria Guenee and Cyclophora serrulata (Packard) ; Lycaenidae: Strymon melinus (Hubner); Noctuidae: Anicla infecta (Ochsenheimer ) Anticarsia gemmatalis Argyrogramma verruca (Fabricius), Elaphria nucicolora (Guenee) Elaphria grata Hubner, Feltia subterranea Hel iothis virescens (Fabricius), H. zea. Pseudaletia unipuncta (Haworth), Pseudoplusia in cludens (Walker), Spodoptera eridania (Cramer), S. exigua, S. dol ichos (Fabricius), S. f rugiperda S. latifascia (Walker), S. ornithogalli (Guenee), and Tricho plusia ni (Hubner); Pyralidae: Elasmopalpus lignosellus (Zeller); Pieridae: Eurema lisa (Boisduval and Leconte); and Tortricidae: Platynota f lavedana Clemens and Sparganothis

PAGE 34

24 sulfureana (Clemens). The total numbers of less numerous lepidopterous species were: 53 E. lignosellus 15 E. acrea 8 S. melinus 6 S. bosqueela 6 E. nucicolora 5 A. pampinaria 4 E. grata 3 A. infecta, 3 P. unipuncta 3 E. lisa 2 P. f lavedana 2 P. virginica and 1 C. serrulata S. sulfureana larvae were collected only from buds and were not observed in beat cloth samples. Twelve of the 27 lepidoptera larvae associated with peanuts are new records: A. infecta A. pampinaria C. serrulata E. lisa E. grata E. nucicolora P. f lavedana P. unipuncta S. sulfureana S. dolichos S. eridania and S. ornithogalli With the exception of P. unipuncta A. infecta, and E. grata some larvae of the other 9 species were reared to adults on peanut foliage. Every year the 3 most abundant lepidopterous larvae were velvetbean caterpillar, corn earworm, and fall armyworm (Table 2). Plusiinae loopers were common in 1976 and 1978, but not in 1977. Beet armyworm was more numerous in 1977 than in other years. Beet armyworms were also extremely numerous on soybean seedlings in 1977 in Florida (Anon. 1977a, Anon. 1977b). Population levels of fall armyworm (FAW) were highest, reaching 17 per sample in Field H on 4 August, during mid July to early August in 1976 (Fig. 2). Field H was the only field where FAW larvae were the major pest that required treatment. In the other fields surveyed in 1976, fall armyworm larvae peaked at 0.5-3.8 larvae per sample with the

PAGE 35

25 exception of Fields C and D where 9 larvae per sample were present the first week of August (Fig. 2). In 1977 larvae began to be abundant in mid-June in Field K and reached highest levels in Fields K and L in mid-July (Fig. 2). The early June abundance of FAW larvae on peanuts in Field K is probably an indication of the outbreak of FAW reported throughout the Southeast in 1977. In 1978 population levels of FAW were low, peaking at 0.6 larvae per sample and 3.1 larvae per sample on 20 July in Field M and Field N, respectively Larvae of FAW were less numerous in 1978 than in 1976 and 1977 (Fig. 3). In fields not treated with insecticides during July a natural decline of FAW larvae occurred during early to mid-August. In no instances were FAW larvae numerous after mid-August. Rearing of Ileliothis spp. larvae on artificial diet indicated ca. 95% of the Ileliothis in 1976-1977 were H. zea (Nickle and Mangold, unpubl.). In 1976 the greatest numbers of corn earworm (CEW) 8.4 per sample, occurred in Field F on 21 July (Fig. 3). The range of maximum densities in other fields surveyed in 1976 was 0.6-4.6 per sample. In 1977 CEW attained very high levels of 19 per sample on 20 July in Field L (Fig. 3). The late planted Field L was probably an exceptionally attractive oviposition site for CEW moths because peak flowering occurred during early July at a time when moths were emerging from field corn. Corn earworm has demonstrated a preference for the flowering

PAGE 36

26 stage of 4 of its major agricultural hosts in North Carolina (Johnson et al 1975). In 1978 CEW densities reached their highest levels of 0.6 and 3.1 in mid-July in Fields M and N, respectively. The patterns of seasonal abundance of CEW for 19761978 were very similar (Fig. 4). In all 3 years CEW larvae were most numerous the third week of July. In fields not treated with insecticides during July, a natural decline of larvae occurred during late July. Corn earworm larvae were never numerous after mid-August. Velvetbean caterpillar (VBC) larvae were first detected in peanut fields the second week of July. Velvetbean caterpillar was the only pest that demonstrated resurgence after insecticide application (Fields B, G, H, Fig. 2). The dynamics of VBC resurgence appear very similar to the resurgence of the same species observed on soybeans (Shepard et al. 1977). In 1976 VBC larvae were most numerous in Field G where 36 larvae per sample were counted on 8 September. Very low numbers of larvae were present in the fields planted early in April; maximum VBC densities ranged from 0.05-0.60 larvae per sample. Maximum larval densities ranged from 0.7 to 7.1 per sample in Fields K and L, respectively in 1977. Highest levels of VBC larvae in 1978 were 8.0 and 2.3 per sample in Fields M and N, respectively. In 1977 VBC larvae increased in number ca. 2 weeks later than in 1976 and 1978 (Fig. 5). In no instances were

PAGE 37

27 VBC larvae present in numbers greater than 1 per sample until August. Velvetbean caterpillar larvae were the only numerous insect pest from mid-August through early October. Adjacent fields of similar planting dates had similar patterns of larval abundance in terms of timing and density — i.e. Fields C and D; and E, I and J. In the 2 cases where planting dates of adjacent fields differed 4-5 weeks, later planted fields had higher larval densities. The late planted Field B, adjacent to Fields I and J, had 5 times more velvetbean caterpillar the third week of August. Similarly, the very late planted Field L had 8 times more velvetbean caterpillar than the adjacent Field K on 2 September. Also corn earworm numbers were 4 times greater in Field L than Field K on 20 July. Therefore, planting early in north central Florida appears to greatly increase the probability of escape from velvetbean caterpillar problems. Peak numbers of ovipositing adults are probably missed by planting early. Also the older plants may be less attractive as oviposition sites than younger plants. There were differences in the average numbers of VBC, FAW, and CEW larvae sampled from various age classes of peanuts 1976-1978 (Fig. 6); Field L was not included because of its atypical planting date. Larvae of VBC were most numerous in peanuts 15-17 weeks old. Larvae o^ FAW fluctuated in abundance, but in general were abundant in peanuts 12-18 weeks old. Larvae of CEW were most abundant in 12 week old peanuts, which is ca. 1-2 weeks after peak

PAGE 38

28 flowering. These data indicate that VBC and FAW larval abundance is probably more related to sample date rather than plant age. Corn earworm larval abundance appears to be more equally related to both sample date and plant age, perhaps because CEW prefers to oviposit in flowering fields. Plusiinae loopers were most numerous from mid-July through August (Fig. 7). Highest densities of loopers were reached in Field D where 2.3 loopers per sample were present on 18 July. Loopers were the most numerous larvae in Field E. Granulate cutworm (GCW) larvae demonstrated no clear seasonal trend between years (Fig. 8). In 1977 and 1978 GCW larvae were most abundant in June while in 1976 GCW larvae were most numerous from late July to early August. The lack of clear seasonal fluctuation may be due to the sampling method. Granulate cutworm commonly spend daylight hours buried in the soil and thus are best sampled between 12:00 AM and 5:00 AM (Eden et al. 1964). Numbers of beet armyworms (BAW) peaked at different times of the season for the 3 years the survey was conducted (Fig. 9). In 1976 BAW larvae were most numerous during late July while in 1977 and 1978 larvae were most numerous in mid-June and early July, respectively. Beet armyworms were never more numerous than 0.7 per sample during this study There were no distinct generations of foliage feeding larvae on north central Florida peanuts detected in this study. Previously 2-3 generations of velvetbean on soybeans were

PAGE 39

29 detected by Menke and Greene (1976) and Strayer (1973). For most species, except for VBC larvae gradually increased over G-7 weeks, peaked, and then gradually declined over 2-3 weeks. Larvae of VBC in early planted peanuts remained at low numbers throughout the season. In late planted fields VBC larvae were present for 5 weeks or more before a sharp increase in numbers occurred. Decline of VBC except for insecticide intervention on late planted fields was very slight The larval development periods of FAW, CEW and VBC on peanuts are relatively long compared to that of other plant hosts (Huffman and Smith 1979, Nickle 1977). The duration of the larval stage is generally 20-30 days on peanuts compared to 12-25 days on other hosts. Parasitism of larvae of fall armyworm and corn earworm is 20-60% (Nickle 1977). Predation further reduces survivors. It is possible that peanuts act as a trap crop or a sink for these pests--i.e. few eggs laid by moths survive to the adult stage.

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30 a H o 4J c o u 43 O > W 0) CO J3 M TJ rH Q) •H tH +J n c CIS 0 o w o •H p •H ;h 0) -p o 00 I> rH I CD Xi 05 0) rH ci H w -p c cu e +-> ni CD !h -P Q) +-> O a; rH CD CD •H N C>H •H C Sh rH CD CD +J CO •H P o Ph C73 rH rH a CD CO tCM CI, 0^ (D (D CO CO CO CD c =3 > 00 '-^ u CO CQ > ^ CQ CD CO O U in o x; ^ a, p o P rH I-? 1-3 W C^ CO CD (Ji I ^ ^ ^ CQ CQ CQ CO CO CO I U U CLJ hJ J J CQ CO o CQ Jh d d • • -co :d cT) 00 CJ CQ ^^ rH C -H O >> -rl lO rH lO lO rH rH CO 00 CD CD CD CD CD CT> I H O CO o X! (X O +J O O O C o E rH •-3 CQ CO U a C c n u o O O rH CD rH d o •H •H H >> CO >>X3 H ^ x; x: x: !h S !h XI ^ •p •p -P d lO O d -p <; d ci d X! rH X3 O CD CD CD CD CD d U U +-I a G C C ci d CD o o O 0 O a, o c c C c c t3 CD CD >> P Jh >. -P d d a cu a d d d Ci Hi d d C <: 00
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31 Table 2. Relative abundance of lepidopterous larvae associated with Alachua County^ Florida^ 'Florunner' peanuts, 1976-1978. „ % of total larvae sampled Species 1976 1977 1978 Anticarsia gemmatalis 38. 7 24 ,4 52. 2 Feltia subterranea 6. 1 4 0 3.0 Ileliothis spp. 14. 8 42, ,6 20. 5 Plusiinae loopers 10, 7 0, .6 7.3 Spodoptera frugiperda 25, 7 22, ,4 13.3 Spodoptera exigua 1. .6 5, ,0 0.4 Other Spodoptera spp. 1, 5 0, 7 1.7 Other 0, 9 0. 3 1.7 "'"Total number larvae sampled 1976, 1977, and 1978 were 15,661 3,403, and 1,982, respectively.

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Figure 1. Location of Alachua County, Florida, peanut fields sampled in survey of peanut arthropods, 1976-1978.

PAGE 44

Figure 2. Mean numbers of FAW, CEW, and VBC larvae sampled from Alachua County Florida peanuts 1976-1978. Breaks in lines indicate dates of insecticide applicat ion

PAGE 45

12 10 8 6 4 2 0 I 2 10 8 6 4 2 0 9 6 8 8 8 0 7 2 6 4 5 6 4 8 4 0 1 2 2 4 16 0 8 0 0 8 8 8 0 7 26 4 5 6 4 8 4 0 3 2 2 4 I 6 0 8 0.0 35 Field A 1976 FAW — CEW VBC Field B 1976 FAW CEW VBC Field C 1976 -FAW -CFW •VBC I \ / \ / \ \ Field D 1976 FAW CFW VBC / 1 1 JUNE JULY AUG SEPT

PAGE 46

gure 2. Continued.

PAGE 47

37 I 425 I 250 I 000 0 750 0 500 0250 0000 IxJ _J Q. < CO 01 LU Q_ cr LU CD < 1x1 8 8 8 0 7 2 64 56 4 8 40 3 2 24 1 6 08 00 36 33 30 27 24 2 I I 8 i 5 12 9 6 3 0 192 176 160 14-1 I : B I I 2 9 6 8 0 6 4 4 8 3 2 I 6 00 Field E PAW -CF.W •VI3C Field F 19/6 FAW CEW -VBC Field G 1976 F-AW -CFW •VBC F leld H 1976 ------FAW a w mc JIINL St PT

PAGE 48

Figure 2, Continued.

PAGE 49

39 LlI _J CL < cr LU Q. (T LU CD < LU 2 6 4 2 2 2 0 I 0 I 6 I 'J I 2 1 0 0 8 0 6 0 4 0 2 0 0 2 8 2 6 2 4 2 2 2 0 1 8 1 6 I 4 I 2 1 0 0 8 0 6 0 4 0 2 0 0 4 8 4 4 4 0 } 6 3 2 2 8 2 4 2 0 1 6 I 2 0 8 0 4 0 0 ;8 2 17 6 16 0 14 4 12 8 1 I 2 9 6 8 0 6 4 4 8 3 2 I 6 0 0 FIELD I 1976 — FAW CEW VBC FIELD J 1976 FAW CEW VBC FIELD K 1977 FAW CEW VBC FIELD L 1977 --FAW CEW VBC JUNt JULY AUG StF'T

PAGE 50

gure 2. Continued.

PAGE 51

41

PAGE 52

Figure 3. Mean numbers of FAW larvae sampled from Alachua County, Florida, 'Florunner' peanuts, 1976-1978.

PAGE 53

43

PAGE 54

Figure 4, Mean numbers of CEW larvae sampled from Alachua County, Florida, Florunner peanuts, 1976-1978.

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45

PAGE 56

Figure 5. Mean numbers of VBC larvae sampled from Alachua County^ Florida^ 'Florunner' peanuts, 1976-1978.

PAGE 57

47

PAGE 58

O CD d W O •H d > O I> ^ ai H -ci 1 CO I> rH E CO CD > cu rH CD u G u o rH fin d •H o m 0 > rH o >^ p U O ^ o E d O d d cu rH s CD CD •H Ph

PAGE 59

49 ^ ro CJ "~ O MOd dO lAJ 16' d3d 3VAdVn ddaiAiriN NV31M

PAGE 60

Figure 7. Mean numbers of Plusiinae looper larvae sampled from Alachua County, Florida, 'Florunner' peanuts, 1976-1978.

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51

PAGE 62

Figure 8. Mean numbers of GCW larvae sampled from Alachua County Florida, 'Florunner' peanuts, 1976-1978.

PAGE 63

53

PAGE 64

Figure 9. Mean numbers of BAW larvae sampled from Alachua County, Florida, 'Florunner' peanuts, 1976-1978.

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55

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SEASONAL DYNAMICS OF PREDACEOUS ARTHROPODS IN NORTH CENTRAL FLORIDA PEANUTS 1976-1978 Introduction Peanuts in Florida are damaged by numerous injurious insects and mites. The most injurious pests in Florida are lesser cornstalk borer, Elasmopalpus lignosellus (Zeller), spider mites, and foliage feeding noctuid larvae. With the exception of data on Labidura riparia (Pallas) collected in pitfall traps in Florida peanuts (Travis 1977) there have been no studies of seasonal incidence of predators. The importance of predators in inducing mortality of pest species has been recognized in other row crops with similar noctuid larval pests such as cotton (Whitcomb and Bell 1964, van den Bosch and Hagen 1966), and soybeans (Buschman et al 1977) There are few reports of incidence of predaceous arthropods in peanuts. Martin (1976) found Coleomegilla maculata (De Geer) and Geocoris punctipes (Say) to be the most numerous predators, with spiders, and 2 reduviids Zelus cervicalis Stal, and Sinea spinipes (Herrich-Schaf f er ) present in low densities in small peanut plots in north Florida. Predaceous insects most commonly found in Texas peanut fields are lady bugs, assassin bugs, lace-wings, ground beetles, predaceous 56

PAGE 67

57 stink bugs, big-eyed bugs, Nabis Orius and praying mantids (Smith and Hoelscher 1975). The objectives of this research were to describe the seasonal incidence, species composition, and relative abundance of predaceous arthropods on peanuts and make preliminary tests of associations between the most numerous predator groupings and major noctuid larval pests. Materials and Methods A total of 14 Alachua County, Florida, growers fields of 'Florunner' peanuts were surveyed during 1976-1978 for relative density of predaceous arthropods. The fields are described in Table 1. Samples were taken at weekly intervals starting on 6 July, 15 June, and 23 June in 1976, 1977, and 1978 respectively, and continued until harvest. A total of forty 0.91 m of row samples were taken at each sample date by the ground cloth method. Samples were taken by folding back the branches and gently placing a ground cloth 0.91 X 0.91 m against plant bases of one side of the row. The peanut canopy was beaten downward vigorously with forearm and hands 6 to 8 times over the cloth to dislodge arthropods. Arthropods that were observed under the branches while inserting the ground cloth or on the ground cloth were identified, counted, and recorded In 1976-1977 samples were taken throughout the field in a manner similar to that used by commercial scouts. All areas of the field were sampled in a random manner with not

PAGE 68

58 more than 10% of the samples within ca. 20 m of field edge. In 1978 samples were taken along the transects of an X-shaped pattern which was aligned along the diagonals of the field. Twenty samples per transect were taken every tenth row in Field M and every thirteenth row in Field N. Each week sampling began on a different row. A test of association between the most abundant predator groupings and lepidopterous larvae was calculated using Kendall's tau-b as suggested by Fager (1957). The Kendall's tau-b statistic is a nonparametric index of order association which conforms to Kendall's criteria for correlation coefficient (Kendall and Stuart 1961). Results and Discussion Due to the difficulty of identifying many of the predaceous species present, certain predators were grouped either in the field or in this report. The composition of the predaceous insect fauna varied considerably with field and year (Table 3). The most numerous predators sampled were ants, spiders, Geocoris spp., L. riparia nabids, and ground beetles (Table 3). This predator complex comprised 91-99% of the predators sampled. Ants were often the most numerous predator observed composing from 13-50% of the total number sampled. In unsprayed fields ants were generally present in over 75% of the samples. The most commonly observed ant species were Solenopsis geminata (Fabricius), Pheidole spp., and Conomyrma insana (Buckley). Whitcomb et al. (1972)

PAGE 69

59 recorded over 60 species of ants from Florida soybeans. Since the crops are grown in the same area and are host to similar pests, the ant fauna of peanuts is probably as complex. Ants were numerous from June through September (Fig. 10). Considered as a group, spiders composed 9.9-45% of the predators sampled (Table 3). In most fields spiders did not exceed 20% of total predators sampled except for Fields K, M, and N. In 1978 spiders were classified into 8 categories as follows: 30.4% other spiders; 19% small spider species and immatures; 15.87o wolf spiders (Lycosidae); 12.87o jumping spiders (Salticidae) 7.0% crab spiders ( Thomisidae ) ; 5.7% striped lynx, Oxyopes salticus Kent (Oxyopidae) 5.5% Chiracanthium inclusum (Hentz) and Aysha gracilis Hentz (Clubionidae and Anyphaenidae, respectively); and 3.8% green lynx Peucetia viridans (Hentz) (Oxyopidae). Spiders were common predators for the entire season and increased in number slowly during the season (Fig. 10). Big-eyed bugs, Geocor is spp., comprised 2.1-16% of the prfdator complex. In 1977. 17.9% of the Geocoris counted were G. ulignosus (Say) adults, 5.7% G. ul i gnosus nymphs, 38.6% other Geocoris spp. adults, and 37.8% other Geocoris spp. nymphs (n=352). In 1978, G. ulignosus adults comprised 24.9% of the total, G. ulignosus nymphs 12.2%, G. punctipes (Say) adults 19.27o, and 43.7% other Geocoris spp. nymphs, and no G. bullatus (Say) adults were sampled (n=213).

PAGE 70

60 From relatively low numbers at the start of the season, Geocoris numbers increased gradually, reached a peak of 0.43 per sample, then declined in number during September (Fig. 11). The striped earwig, L. riparia fluctuated widely in abundance between fields composing 1.8-47.4% of beneficials sampled. Most of the L. riparia sampled were observed while parting the foliage in preparation for beat cloth placement. Labidura riparia numbers climbed rapidly from very low initial numbers to greatest numbers of 1.1 per sample at the season's end (Fig. 10). Mark-recapture analysis of absolute earwig population levels in 2 Alachua County peanut fields during late August and early September indicated maximum populations of 34,400-85,227 earwigs/ha (Travis 1977). Nabids were relatively abundant only midway through the season and a decline in nabid numbers occurred in September (Fig. 11). In 1976 Tropicanibis capsif ormis (Germar) and Reduviol is roseipenn is (Reuter) composed 99 and 1%, respectively, of the total nabids collected for identification (n=100). Of 240 nabids sampled in 1978, 96% were T. capsi f ormis 2.5% were R. roseipenn is and 1.5% were Pagusa f usca (Stein ) Adults of the insidious flower bug, Or ius insidiosus (Say), reached peak abundance during mid-June and July, then declined sharply (Fig. 11). Patterns of abundance of 0. insidiosus may be associated with peanut flowering since

PAGE 71

61 pollen seems to be an important part of diet of both nymphs and adults (Dicke and Jarvis 1962). Also, tobacco thrips are most abundant before flowering and may serve as prey. Ground beetle adults and larvae composed 3.2-9.5% of the predator complex. The most numerous species of ground beetle were the foliage dwelling Cal 1 ieda decora (Fabricius). Cal lieda decora comprised 75 and 53% of the carabids sampled in 1977-1978 respectively, Peak abundance of C. decora larvae occurred near peak numbers of fall armyworm and corn earworm. Collurius pennsylvanicus (Linnaeus) adults composed 7.3 and 47% of the carabids collected in 1977 and 1978, respectively. Other carabids infrequently encountered were adults of Anisodacty lus merula Germstacker, Selenophorus palliatus Fabricius, S. ellipticus Dejean and Teragonoderus intersectus Germar and larvae of Progalerit ina spp. and Calosoma say i Dejean. Many of other predaceous arthropods occurred in numbers too low for assessment of their seasonal dynamics. None of these predators averaged more than 0.5 per sample on a given date during this 3 year study. Some of the predators that were observed in most fields in low numbers include: Doru taen latum (Dohr) ( For f icul idae ) Spanogon icus albof as ciatus (Reuter) (Miridae) Zolus cervical is (Stal) (Reduviidae), Sinea spp. (Reduviide), Podisus macul 1 ventrus (Say) (Pentatomidae ) Chrysopa spp. larvae ( Chrysopidae ) Scymnus spp. adults ( Coccinel 1 idae ) and Noxtoxus spp. adults ( Anthicidae)

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62 Classical predator-prey theories predict gross predator population density fluctuations similar to the host-population's gross variations (Watt 1968). Significant positive correlations demonstrate associations or similar patterns of variation between larvae and predaceous arthropods. The explanation for association may be chance, or indicative of density dependence phenomena. Spiders were significantly correlated with foliage feeding larvae (FFL) twice, velvetbean caterpillar (VBC) 6 times, and fall armyworm (FAW) once (Table 4). For earwigs there were 6 significant associations involving FFL once and VBC 5 times. Nabids had the greatest total number of correlations. Nabids were correlated with FFL 4 times, VBC 11 times, and FAW once. Geocoris spp. showed few correlations; they were associated with VBC twice, FAW twice, and CEW twice. Ants were associated with VBC once, the fewest significant associations of all predator groupings. Orius insidiosus adults showed significant correlations with FFL twice, FAW 3 times, and CEW 3 times. For further elucidation of association patterns a refinement in sampling technique and statistical analysis is needed. Absolute samples or calibrated relative samples of pests and beneficials analyzed using multivariate analysis may prove useful in clarifying associations. Some inferences about the relative importance of predaceous arthropods on north Florida peanuts can be made.

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63 Ants were the most numerous predators sampled and probably one of the most important predators regulating pest populations. Ants have been frequently observed consuming lepidopterous eggs in Florida soybeans (Buschman et al 1977, Nickerson et al 1977). Lack of many significant correlations between larvae and ants is not surprising considering ants were one of the most under-sampled predators in this study. Some species of ants only forage at night (Whitcomb et al 1972) and most ants are underground at any given time. Because of the abundance of families represented spiders occupy a variety of feeding niches. Whitcomb (1974) stated 4 important roles of spiders as follows: (1) spiders prey on destructive insects; (2) spiders serve as food for predators; (3) spiders tend to be general feeders, and (4) spiders compete with insect predators for prey. Spiders have been reported as important egg predators in Florida soybeans (Buschman et al 1977). The abundance of spiders in peanuts suggests they are important in effecting pest population dynamics Eggs and small larvae of noctuids are part of prey of Geocoris spp. However Geocoris spp. consume a very broad array of prey (Crocker 1977). Menke and Greene (1976) reported large Geocoris spp. populations exerted little population regulation of velvetbean caterpillar populations in north Florida soybeans. Consequently, Geocoris spp. were probably not major predators in north central Florida peanuts.

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64 The habits of ground beetles are extremely varied often within the same genus. Callieda decora was the only ground beetle sampled in sufficient numbers to be important in some fields. In 1977 C. decora was observed numerous times feeding on small to medium corn earworms. Calosoma sayi adults and larvae were numerous in pitfall traps in peanut fields with high VBC populations in 1976 (Travis unpubl.). Calosoma sayi consumes and reacts to noctuid pests of soybeans by taking progressively more prey items as they become available (Price and Shepard 1978). Calosoma sayi is one of the few potentially important predators of large larvae and pupae in peanuts. Labidura riparia were important predators in most fields during this study. Earwigs were especially uncommon in Field N in 1977; it is possible that application of parathion on 6 July followed by a 27 July application of monocrotophos may have greatly reduced the earwig population in this field. All stages of noctuids may be consumed by L. riparia (Schlinger et al. 1959, Hasse 1971, Neal 1974). In laboratory tests functional response of earwigs to noctuid larvae prey indicated that successful attacks increased with higher host density (Price and Shepard 1978). That L. riparia. numbers were associated with foliage feeding larvae was demonstrated by significant correlation coefficients and the gradual increase in earwig numbers during the season (Fig. 10). L. riparia is considered an important predator

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65 in Florida soybeans (Neal 1974, Buschman et al 1977). Labidura riparia is probably one of the most important predators in peanuts in north central Florida. T. capsif ormis adults and nymphs were potentially important predators of VBC larvae. The increase in nabid populations closely followed the increase in VBC larvae. Nabids were uncommon earlier in the 3 seasons when FAW and CEW were present. Nabids consume eggs and small larvae of noctuid pests. 0. insidiosus was not numerous during the season when defoliators were numerous. However, 0. insidiosus may have served to suppress early season outbreaks of some pests during June. During the increase in VBC numbers 0. insidiosus were not common.

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66 13 CD B rt (/) 10 o p a fH (U •H nJ a. (U 13 rO c a; O I/) •H •H 1 — 1 u u Sh fH 3 in 13 3 in !U o 13 x) C t/l -a 4-> T3 o •H •H 3 3 •H o .o XI o •H 0) n) !h ^1 -J C3 o fH

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67 > "O — ( tu f-H •rH Uh DO 1 — t c X H .£) T3 0) (L) to M-l X c 0) bO rH nl o •H •fH r-i Uh o t4H CU O o 3 O to c $-1 -M o (1) 3 H C P ri o — 1 CL) UJ •H D (-1 O r— 1 (D u C C c Q (D 3 0) O p .— ( vi u nJ o o r i r-LOO^OOOTtvOvDOO u->f-HLOOr--^r~-o to o-i o Tt rg Lo to O) o LO vO CM (N) 00 o OO ,-H to lO .— I LO 1^ r-H r-H to lO 00 lO CnI to r-j to un to in \0 00 to r j LO Lo n LO vc to 1 o o 1^1 o O r^l O O to ^ f-H .— I O VO f-H ,-H O --f f-H 00 r-f-H ri -X -X ^ t~f-H O I ^ rt OO ^ r-1 I I o 00 LO LO o to Ol t~^ f-H to to u^ ci en to to to cn vO 00 to I 00 to 00 \0 ^ o LO O LO rj in LO LO f-H ,-H LO \0 \D rj to LO O f-H CD LO LO LO f-H 00 to CM t fN LOCT>MT}-.-HOt~^LOC^lCTlOOr^ rM^otOf-HCNjotO'^i-f-HtOLO Tt CD f-H LO O T^I to CD ra CM \0 CM t: ooLoooLOvOtovDf-HLntor--co olo f-Hf-HOOf-Hf-H^CMCNlf^ff-Hfrt tO(M -X •X ^ (D f-H to O \D Tt v£) LO OD t^J LO -^t t-~ to r-I to LO ^ n -)to n r^i LO to f-H f-H f-H o TtLOr^-CMOf-HCDCD to TlLO (M to LO to OtOLO tOO-trff-Hi— (f-H'Tt-r^ r-1 to LO o to rj ,-H rj rH to -^OOOf-HtOOOOOO ,-H(^LO(Mrvir~-00Tt III I I X X -x r.)Tt.-H(OLO.-HO\Or~^rtlOf-H rio^LOr-if-Ht~-c^ioo\Ot-H o ^ LO r~o LO rj to (NlOr^^f^l-r-Ht^LO I I I I I I CDt~--OCDCDvOOf-Hf-Hf— (f-H ^^^LOCMtOrjT^CMtOLO X to TJto a, t-Lc < LO r 1 LO CI to to 1 to •^ 1 00 to t^ O 1 to 1 o 1 -J U ,-J U-, UJ LU, LL. I-L, > u IX ci ft w in H u fH (D O U rH O CL, (U CO 00 to I I •X -x X -x CD CD r-O LO \0 f-H to O vO f-H I I I I -X X CM \a •X -x r^J^.;:j-,.H\Of-HCDO I I lx'-t:caiJUtxua.pu>u oj 03 •fH 3 ^1 X) 03 •H D. X H OS u to • fH X 03 Z ^ ^ LO fO LO 00 o o LO 00 f-H O O CD (D LO \D LO 00 CXD CM (M O vO to o LO to I X CD •tj1 LOtOt^C^ILOLOLOLO f-H f-Ht-H o-t'*LO,-HtOLor-j LOOtoLO -x ,-H O 00 ,-H ,-H vO r-H VD LO cn to to O tN J U S: tx < 03 m tx u. > u 3 ifl O •H -o to • fH 3 •H ns !h •H O ,-H > T-H LO o • o II CL, •M tH f-H 03 1 — 1 > 0) f-H !h 0) f-H 4-1 o CI, O o -o •H II &, (U Cu rH P f-H o3 f-H O) P C t4H rt o o •-H e tp 3 •fH to c II •H CO rj IX X IX X

PAGE 78

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PAGE 79

69 o in o 9 P ro c\j oj ~~ ~ MOd JO lAI 16 U3d SdOlVQJdd dJat^JflN NV3L^

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PAGE 81

71

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SPATIAL DISTRIBUTIONS OF DEFOLIATING LEPIDOPTEROUS LARVAE ON PEANUTS Introduction Spatial distributions are a useful means of quantifying the dispersion of insects in a given habitat. Spatial distributions are useful in several ways: (1) to aid in determining the appropriate transformation for analysis of variance; (2) to develop sequential decision plans; and (3) to develop sampling plans. Also, inferences about the biology of the insect e.g., dispersal patterns, can be made. Spatial distribution models are probability distributions that relate the frequency of occurrence of an event, depending on the mean of the measurements and in some cases on one or more parameters. The most useful statistical distributions in entomological research have been the Poisson and negative binomial (Southwood 1978). The Poisson distribution describes a random distribution with variance equal to the mean. Most commonly in insect sampling the variance will be larger than the mean, indicating that the distribution is aggregated or clumped. The most useful distribution describing a clumped insect population has been the negative bionomial. 72

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73 The versatility of this distribution arises from the fact that it may be derived from at least 5 different models (Waters and Henson 1959). The objective of this study was to determine the spatial distribution of the major foliage feeding insect pests of peanuts in Florida. Methods and Materials Forty samples per week were taken by the ground-cloth shake method from 0.91 m of row from growers' fields of 'Florunner' peanuts, 1976-1978. Thus the field counts of foliage feeders were taken from different field sizes and population densities. Insects sampled included velvetbean caterpillars, Anticarsia gemmatalis Hubner; fall armyworm Spodoptera f rugiperda (J. E. Smith); corn earworm, Ileliothis zea (Boddie); granulate cutworm Feltia subterranea (Fabricius); •and Plusiinae loopers : Trichoplusia ni (Hubner), Pseudo plusia includens (Walker), and Argyrogramma verruca (Fabricius). Mixed populations of loopers prohibited differentiation of these species in the field. Data sets were arranged into discrete frequency classes and fitted to mathematical distributions utilizing a computer program developed by Gates and Ethridge (1972). Only those data sets with 4 or more frequency classes were analyzed and fitted to a distribution. The observed

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74 frequency distribution for the following distributions: Poisson, Poisson-binomial Poisson with zeroes, negative binomial, Neyman type A, and Thomas double Poisson. The iterative solution technique of Bliss and Fisher (1953) was used determining the parameter k of the negative binomial. Common k values were calculated by the iterative method (Formula 10) of Bliss and Owen (1958). Results and Discussion Data sets of counts of lepidopterous larvae fitted the negative binomial or Poisson with zeroes better than any other distribution (Table 5). Data sets obtained from counts of fall armyworm and velvetbean caterpillar fit the negative binomial significantly better than Poisson. The percent fit of data sets to the negative binomial for all larvae was relatively high — i.e. 82-90% while similar studies in soybeans by Shepard and Garner (1976) and in cotton (Kuehl and Fye 1972) showed lower fits of negative binomial for some of these same species. The Poisson distributions fit the data fewer instances, 41-70% in every case Values of common k for larvae were 3.93 for fall armyworm, 5.20 for corn earworm, 7.27 for velvetbean caterpillar, 2.51 for granulate cutworm, and 3.58 for loopers. Only the o former 2 common k values significantly fit (P=0.05) a test for homogeneity of k in the different samples.

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75 The value of k may not be a constant for a population but often increases with the mean. However, regressions of 1/k versus population means for individual species were not significant P=0.05. This indicates that k values and means were not related. Large variation in sample k values caused the lack of fit. Neither size or age classes of larvae were considered in fitting distributions. Grouping instars may have increased the k values by combining the different instar distributions. When action economic thresholds for peanuts are revised sequential sampling plans may be developed using the formula presented by Waters (1955). The common k values determined for fall armyworm and corn earworm can be used for calculating decision lines. The formula for decision lines for populations described by the Poisson distribution will be adequate for the other species of lepidopterous larvae.

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76 Table 5. Percentage fit of counts of foliage consuming lepidopterous larvae to the expected frequency distributions, 1976-1978. Fall Corn^ 3, Velvetbean Rank armyworm % Fit earworm % Fit caterpillar 1 Neg. binomial 84 Poisson /zeroes 84b Neg. binomial 2 Neyman 73b Neg. binomial 82 Neyman 3 Poisson-bin 69b Neyman 82b Poisson-bin 4 Thomas 66b Poisson-bin 77b Poisson/zeros 5 Poisson/zeros 65b Thomas 73b Thomas 6 Poisson 41d Poisson 61b Poisson Number of observed frequency distributions equals 51 for FAW, 44 for Ileliothis spp., 39 for VBC 33 Cor loopers and 28 for GCW % fit not significantly different from the % fit of the negative binomial distribution at the 57o level % fit significantly different from % fit of negative binomial at 5% level % fit significantly different from % fit of negative binomial at 1% level

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77 Table 5. — Extended Granulate % Fit Loopers^ % Fit cutworm % Fit 87 Poisson/zeros 94b Neg. binomial 90 80b Neg. binomial 88 Neyman 85b 77b Neyman 82b Thomas 85b 74b Thomas 79b Poisson/zeros 82b 61b Poisson-bin. 73b Poisson-bin. 75b 54c Poisson 70b Poisson 68b

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EFFECTS OF UNIFORM HAND DEFOLIATION OF PEANUTS ON PLANT GROWTH Introduction Peanut (Arachis hypogaea L.) yields in the southeastern United States may be reduced by a complex of arthropod pests. Most of the insecticide applications in the southeastern peanut belt are made to control foliage feeding noctuid larvae (French 1973). Foliage feeding larvae reported capable of causing yield loss include corn earworm, Heliothis zea (Boddie), fall armyworm, Spodoptera f rugiperda (J. E. Smith), and velvetbean caterpillar, Anticarsia gemmatal is (Hubner) (Bass and Arant 1973). In Florida, noctuid larvae may become numerous 10 weeks after planting and damaging levels of larvae may occur until harvest. Information relating peanut foliage loss to yield is variable for a given plant age and variety. Previous defoliation experiments have dealt with peanut varieties other than 'Florunner' (Enyi 1975, Williams et al. 1976, King et al. 1961) or have examined only the influence of defoliation of 'Florunner' on yields only (Greene and Gorbet 1973, Nickle 1977). A mowing machine was used by Greene and Gorbet (1973) to remove the upper portions of peanut canopies to approximate 5 levels of defoliation of 'Florunner' peanuts in 7S

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79 Florida. Removal of an estimated 33% of leaf area reduced yields 5-44% except for a 2% yield increase at 81-90 days after planting. Yield reductions averaged for the 3 years of defoliation experiments at 58, 65, and 108 days after planting were 3.8, 13, 21.5, and 44% yield loss from 10-15, 20, 33, and 50% defoliation, respectively. At the 507o defoliation level some stems and pegging branches also were removed. Nickle (1977) hand defoliated unirrigated 'Florunner' peanuts in Florida at 5 dates. Yield reductions averaged 2-6.8, 7.2-21.6, 16.8-41.2, and 20-51% from 25, 50, 75, and 100%. defoliation respectively for the 2 defoliation experiments. Greatest yield reductions for both experiments resulted when defoliation occurred at 63 days after seedling emergence. Few studies describe how defoliation affects peanut canopy characteristics and plant growth. Boote et al (1980) reported the effect of 75% hand defoliation of the upper 42% of canopy leaf area of unirrigated 'Early Bunch' peanuts. Measurements were made of light interception, specific leaf weights (SLW) leaf area index (LAI), apparent canopy 14 carbon exchange, and photosynthet ic uptake of CO^ 4 days after defoliation. Effects of defoliation on peanut growth and yield are being quantified using a modeling approach (G. Wilkerson"*") Simulation of peanut defoliation '"Ms. Gail Wilkerson, graduate assistant, Univ. of Florida.

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80 will enable the experimental control of the many interacting factors (environment, insect populations, crop phenology) at will. Current peanut plant growth models (Duncan 1974, Young et al 1979) lack components for coupling defoliation to plant growth. Objectives of the present study were to describe how defoliation affects canopy characteristics and plant growth. Materials and Methods Peanuts cv. 'Florunner' were hand planted in 3 blocks 42m X 22 rows 22-23 May 1978 at the University of Florida Agronomy Farm, Alachua County, Florida. The soil type was Arrendondo fine sand. Row spacing was 76.2 cm with plants spaced 13.8 cm apart in the row, which is within the range of plant population for maximum yield (Malagamba 1976). Weed control was achieved with preplant ( 6 kg a.i./ha benfluralin and 2.3 kg a.i./ha vernolate) and cracking time (2.8 kg a.i./ha dinoseb and 2.4 kg a.i./ha 2,4-DEP) herbicides. Ethylene dibromide (253 ml/chisel/lOOm) was injected 5 days before planting for nematode control. Gypsum was applied by hand at 1700 kg/ha on 26 June. The fungicide chlorothalonil was applied at 0.8-1.1 kg a.i./ha starting on 22 June at 7-10 day intervals until 22 September. Monocrotophos (1.9 kg a.i./ha) was applied on 29 June for lesser cornstalk borer ( Elasmopalpus lignosellus (Zeller)). Either methomyl ( 6 kg a.i./ha), carbaryl (1.2 kg a.i./ha) or

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81 acephate (1.1 kg a.i./ha) were used to kill foliage feeding noctuid larvae (corn earworm, velvetbean caterpillar, fall armyworm, and Plusiinae loopers) and were applied at 7-14 day intervals from 15 July until 22 September. Insecticides and chlorothalonil were tank mixed and applied with a pressurized backpack sprayer. On 24 August f ensulf othionPCNB granules (40.3 kg a.i./ha and 13.4 kg a.i./ha, respectively) were broadcast by hand to slow the spread of white mold, Sclerot ium rolf sii Sacc. infestation. Overhead irrigation was used to prevent extreme water stress. Pesticides and cultural practices used were designed to minimize pest damage and still be reasonably similar to typical grower practices. Four levels of defoliation were obtained by removing 0, 1, 2, or 3 leaflets from all tetraf foliates with a petiole extension, corresponding to 0, 25, 50, and 75% defoliation, respectively. Fifty leaflets from 3 plots of each defoliation treatment were saved for leaf area determination with an automatic area meter and drying at 70 C. Defoliation and check plots were selected for uniformity at 5 weeks after planting and assigned randomly to treatments. Defoliation plots were 1.1 m lengths of row with (1) at least 1.5m between plots in the same row and (2) undefoliated adjacent border rows. Plots were defoliated at 25, 50, and 75% at 8, 11, 13, and 15 weeks after planting. At 17 weeks the only defoliation level was 75%. In addition.

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82 there was (1) a treatment at 8 weeks of 75% defoliation plus removal of buds for 7 days and (2) a redef oliation treatment of 75% defoliation at 15 weeks of some plots 75% defoliated at 11 weeks. At 2 week intervals, starting 2 weeks after a defoliation, until harvest at 19 weeks after planting, 3 samples of 75% defoliated plots of 11, 13, 15, and 17 weeks were removed. At 19 weeks after planting 4 plots of all treatments were harvested for yield. Similarly, undefoliated plots were removed at 8, 10, 11, 13, 15. 17, and 19 weeks. Four replicate samples of the 8th week defoliations also were removed at 10 weeks. One plant from each plot, not one of the plants bordering undefoliated plants in the row, was separated into roots, stems, leaves, pod shells, and kernels for dry weight determination. The remaining plants in the plots were dried and total plot weights were obtained by summing plant parts of a plot and remaining plants. Leaflets from undefoliated plots were separated into leaflets present at defoliation ("old" leaves) and intact leaves ("new" leaves) expanded since defoliation date. Leaf area and dry weights were measured from 50 "new" and "old" leaves. Single plant part percentages and total plot weight were used to calculate dry weights of plant parts per unit area The photosynthetically active radiation (PAR) intercepted by peanut canopies was measured 1-3 days after defoliation using a pyranometer (LI-200S)^ in conjunction with

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83 a quantum-radiometer-photorneter (LI-185) and pringing integrator (LI-550)"'". Photosynthetically active radiation measurements were taken 1-3 days after defoliation on days of clear skies between 900-1500 hours EST. A metal track 3 wide with 3 cm sides was inserted perpendicular to the row between plants. The pyranometer was pulled by its cord manually along the track at a timed constant rate for 1 minute. An ambient full sun reading above the canopy was recorded within 1-2 minutes of canopy reading. Results and Discussion The daily rainfall, irrigation, solar radiation, maximum and minimum temperatures from planting until harvest are given in Appendix Table 12. Percent light interception of peanut canopies under different levels of defoliation at different plant ages is given in T.ble 6. The LAI for intact canopies was 3.11, 4.52, 5.65, 6.09, 5.53 and 5.45 at 8, 11, 13, 15, 17, and 19 weeks after planting, respectively. Quadratic regressions for LAI and percent light interception of intact canopies and of canopies defoliated 27-75% at 8, 11, 13, 15, and 17 weeks after planting were calculated (Fig. 12). Two LAI — percent light interception coordinates taken at 6.5 and 9 weeks after planting used in the ''"Lamba Instruments Corporation, Lincoln, NE

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84 intact canopy regression were taken from an adjacent peanut experiment (G. Wilkerson unpubl.)Differences in canopy structure at a given LAI is a probable explanation for the difference in regression equations of light interception — LAI for intact defoliated canopies. In general, most of the LAI data used to fit the defoliated canopy curve represent canopies with greater stem areas and ground cover. Ten of the 13 defoliated canopies had an LAI less than 3. Of these 10 canopies, 7 were from plots 11 or more weeks old. Stem growth is almost complete at 11 weeks and stems intercept 39% of ambient light when 2 leaves are removed from full grown plants (Jones et al. unpubl.). By 11 weeks ground cover was 100%. The stem light interception plus the possibly more uniform spacing of leaves on plants exhibiting 100% ground cover compared to intact canopies with a LAI less than 3 probably caused the higher light interception readings of defoliated canopies at a given LAI To estimate the difference in crop and pod growth rates of intact and 75% defoliated canopies at 11 and 13 weeks after planting, linear regression curves of dry weights versus plant age were calculated. Since more photosynthate is necessary for kernel development than other plant parts, a result of the higher concentration of oil and protein in seeds than in other plant parts, an adjustJ. W. Jones, C. S. Barfield, K. J. Boote, G. H. Smerage, and J. Mangold. Photosynthetic recovery of peanuts to defoliation at various growth stages. MS in review.

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85 ment was used. Average values of the correction factors developed by Hanson et al. (1961) and Penning de Vries (1974) for seeds--i.e. 1.88 X kernel weight were used. The growth response of intact plants, 75% defoliation at 11 weeks, and 75% defoliation of plants at 13 weeks is illustrated in Fig. 13. Regression equations for crop and pod growth rates are presented in Table 7. The crop growth rate of intact canopies appeared to slow late in season. The decrease in growth rate was probably due to the few new leaves that are added and the photosynthetic rate of older peanut leaves decreases with age ( Trachtenberg and McCloud 1976, Henning et al. 1979). There was a greater relative reduction in pod and crop growth rate of plants defoliated at 13 weeks than at 11 weeks. For plants defoliated 75% at 11 weeks, crop and pod growth rates were 71.7 and 76.1%, respectively, that of the undef oliated Seventy-five percent defoliation at 13 weeks reduced crop and pod growth rates by 65.3 and 57.1% that of the undefoliated plants. A plausible explanation for the larger reduction in growth rates of 13th week defoliated plants versus 11th week defoliated plants may be related to the lower average LAI present of 13th week defoliated plants during the remainder of the growing season. Plants defoliated in week 11 added LAI. Partitioning coefficients were calculated from the crop and pod growth rates. Partitioning refers to the division

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86 of photosynthate between reproductive and vegetative plant parts. Previously pod partitioning coefficients of undefoliated 'Florunner' peanuts has been estimated at 73% by linear regression of dry weights (McGraw 1977) and 84.7% by the PENUTZ model (Duncan et al 1978). The calculated pod partitioning factors for the undefoliated plots from 11-19 weeks and 13-19 weeks. 75% defoliation at 11 weeks, and 75% defoliation at 13 weeks were 75.1, 80.9, 70.7, and 92.5% respectively Specific leaf weights of defoliated plants significantly increased in some cases after defoliation as compared to undefoliated plants (Tables 8, 9). Most of the increase in SLW was attributed to the increase in "old" leaf SLW. Old leaves increased in SLW probably due to less shading. Decreases in SLW with shading for peanuts (An 1976) and other legumes such as alfalfa, Medicago sativa L. (Wolf and Blaser 1972) and soybean, Glycine max (L. ) Merr., (Cooper and Quails 1967) have been reported. An increase in SLW may be related to increased photosynthetic rates. Bhagsari and Brown (1976) detected a significant positive correlation between SLW and photosynthesis in 1 of 3 experiments involving peanut genotypes. However, no correlation between SLW and net photosynthesis of peanut leaves were found by Pallas and Samish (1974). Defoliation reduced yields at most levels and plant ages, but significant differences from undefoliated peanuts

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87 occurred only with 75% defoliation at 8 weeks plus removal of buds for 7 days, 757o defoliation at 11 weeks, and multiple 75% defoliations at 11 and 15 weeks (Table 10). Early pod fill ca. 68-day-old plants has previously been shown as the plant age most sensitive to defoliation (Nickle 1977) Consumption or damage to terminal buds appeared to be an important compounding effect to uniform canopy defoliation. The early instars of corn earworm feed selectively on leaf tissues of terminal buds (Morgan 1979). Sustained terminal bud damage may be an important aspect of defoliator damage by corn earworm and possibly fall armyworm especially during the vegetative growth stage of peanuts. Seventy-five percent defoliation and 75% defoliation plus removal of buds at 8 weeks reduced pod and stem weights at 10 weeks (Table 11). Decreases in stem weight of 'Dodoma' edible peanuts with defoliation have been reported previously (Enyi 1975). The weight of leaves grown 2 weeks after 50 and 75% defoliation also was significantly higher than undefoliated plants. Defoliated peanut plants compensated for defoliation by growing more leaves and reducing stem and pod growth. Plants defoliated 75%. at 11 weeks grew significantly more leaves than undefoliated plants during the 2 week period following defoliation (Table 11). No detectable differences in leaf growth between defoliated and undefoliated plants were detected in other treatments or time periods after defoliation

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88 Table 6. Average percent light interception of intact and defoliated 'Florunner' peanut canopies after def ol iat ion Percent Percent light interception defoliation Defoliation date (weeks after planting) 8 11 13 15 17 19 Intact 69. 5 90, ,6 96. ,9 94 0 92, ,9 95. 5 25 68. 3 83, 1 91. 2 81. 8 50 57. 5 80. 0 75. 8 77. 2 75 51. 8 63. .4 70. 5 50. 7 60. ,6 75+buds 45.2 Buds removed for 7 days.

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89 CO O u u o u o •H a M o tfl -H (M X3 o CO -H •H m c e c o G •H O w •H 4-> ^^ :=! bC 0) PS c o •H +-> (D :^ 0) -C! CD 4-> ci •H i-l 0 ^-^ (D -d +-> 0) -H O 0 O t> in X X CO (M lO o CM + (X) CD in o in I II I II CO CO 1-1 o in i-H rH + + in f— I in CD O) I I II II in o ^1 p a o o in o u -p a o o CO CO o o • • • •H 0 CD •H & 0 (D (D P> m c • • 0 s x: x; CO 0 o in 00 ^1 • • o iH 1—1 1—1 d + + m 0 CD O e • CM • !h 0 GO O n P p 1 o II II bfl ^-^ •H C o :=! •p CM P' O o o m • • 0) 0 p> d o f-{ o CD CM >> p • o X X rH (D bC P" w iH + + o in -o o • nS pH 0 0 00 !-i 1 1 0 Ti II II & 0 >< ft m p> 0 x; x: bD p" Cj) cni H r-l iH 0 p 1 1 pS c: CO CO 0 1—1 1—1 T! O 0 ^1 CM bC P" X! ta •p 0 & • w 'd >) o d aT3 II II >i X

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90 Table 8. Specific leaf weight (SLW) of peanut leaves from intact and defoliated 'Florunner' peanut canopies in relation to weeks after planting. Age at 75% SLW (mg/cm) defoliation Leaf weeks after planting (weeks ) type 11 13 15 17 19 1^ o n "t" T* o T 3 83 3.83 3 86 4 03 4.12 11 new 3 85 4.19 4 62 4 bo old 4.12 4.20 4.63 4.76 avg. 4.02 4.26 4 .63 4.72 13 new 3.09 4.78 4. 51 old 4 20 5. 00 4.91 avg. 4. 06 4.96 4.80 15 new 4.01 4.12 old 4.15 4 90 avg. 4. 10 4.80 17 new 4.39 old 4.51 avg. 4 .49 LSD for new leaves, old leaves, and svg. leaves=0.39, 0.45, and 0.47, respectively, P=0.05.

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91 in o X2 • d d d d o CD O in CO a O rH in c ft rH CO CO CO CO CO ^ — U p> c c o 0 5h CO W 0

d d d d tp d CD CD •P rH s CM CO O CD XS o rH • • • CO CO CO CM >. p & rH S 0 Pl c ST. C d j5 CJ •p 'p m •p c Q) > bfl d d d d d p C 00 00 CO O rH in in rH • • • +J o -o CO CO CO O rH rH CJ O 0 ^1 XS d rH 0 U 0 • KJ pi OH (U pi 0) -P S > X3 d d o 0 S C d CO rH o in rH CD CD 0 d 0 >> S 0 •P a u 0) 00 CD O rH CM d rH XS p> \r 00 00 0 d • o m CO CM CM CM H rH rH w m ^ a rH >, d O 0 d T5 o c\i xi rH O rH -t< E P" o :i rH ^1 pi in CO CD CO rH 0 O o w CM o e tp (D pi o =p ^1 cp oS CM d 0 0 w a c w CJ > o CJ o •H :i •H Cfl s pi 0 G) Oj rH rH Crt c !H •P 0) O + 0 d rH > 65 ^1 ;=i o m rH O CD P> in o in in rH CJ ^-\ rH c CSl in i> d d d) o > Q Q o rH CM

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92 Table 10. Effect of defoliation of 'Florunner' peanut plants on plant parts at 19 weeks. Level Yield Age defoliation reduction Pod dry^weight defoliated % % (g/m ) control 0 • 0 495, lab 8 25 4 02 475 Oabc 8 50 15. 06 420 5abcd 8 75 13. 24 429 5abcd 8 75+buds 26. 19 365 .4cd 11 25 6. 48 463 Oabcd 11 50 18. 54 403 3abcd 11 75 29. 50 349 Od 11 15 75 26. 05 366 led 13 25 30 493 5ab 13 50 1 60 503 Oa 13 75 23. 64 378 Ibcd 15 25 6. 00 465 3abcd 15 50 10. 30 444 labcd 15 75 21 90 386 6abcd 17 75 20. 20 394 Sabcd Values in a column followed by same letter are not significantly different (?< 0.05), Duncan's new multiple range test

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93 Table 11. Dry weight of leaves from Intact and defoliated 'Florunner' peanut plants 2 weeks after defoliation. Week of Def oil ation N f^\M l"i W J. d V o o 1 2 Dry weight (g/m ) defoliation treatment Week added 11 75% 11-13 40.38a control 11-13 20.66b 13 75% 13-15 12.06a control 13-15 16.88a 15 75% 15-17 9 03a control 15-17 -10.60a 17 75% 17-19 4.29a control 17-19 2.06a Values in a column, for a given week of defoliation followed by same letter are not significantly different (P<0.05), Duncan's new multiple range test.

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+-> d O CD 73 O rH l-H 0) <; > 0) rH O P r-l O C • O O •H II +-> D•• (U -P O d %^ 0 +-> -P c C cj •rH O •H X3 -H h£) C •H hD rH M -P C 0 O ^^ -rH (U W CD P. (U > •H 0 m D bD 0 rf 0 a u +^ -P c O O •H O P" +-> -H c! tp Jh 'H -H -C! C d "id he (yarn 0 •H P4

PAGE 105

95 N0lld33d31NI IHOn lN33d3d

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Figure 13. Dry matter accumulation in peanut plant parts in relation to weeks after defoliation. Pod weight is adjusted by factor of 1.88 X kernel weight

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97 1800lf>00 MOO 1200 1000 UJ cr
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APPENDIX Table 12. Solar radiation, temperature, rainfall and irrigation during growing season, 1978. Solar radiation Temperature (C) Rainfall and Day (Langleys) Max. Min. irrigation (mm) 23 ivicty 4: y o o o 21 i 94 O 1 I 21 / /I Q o o o o 20 6 5 1 oy o 32 o O 20.0 97 bl4 21 r-j f 16 1 9R ODD r-r 1 18.3 9Q 31 7 18.3 OU r\ 32 2 20 0 O 1 o n "7 39 / 32 2 19.4 5 8 i June ooO 32 o 8 20 0 9 o ri o 392 31 1 22 2 o O 292 30 0 21.7 25. 9 277 28 3 22 2 8 8 O 368 28 3 21 1 b 485 31 1 22. 2 I 540 31 1 23 3 .5 O o rz r\r\ o02 33 3 24 4 9 425 32. 2 23.9 2.5 10 449 31 7 23.9 14.7 11 449 31. 7 23.3 .3 12 461 31 1 20.6 13 576 32. 2 23. 3 14 456 31 1 23.3 7.9 15 464 28. 3 20.0 16 519 30. 6 18. 9 17 619 30. 6 18.9 18 614 30. 6 17. 8 19 507 30. 6 22. 2 20 313 29. 4 22. 2 21 406 32. 2 21.1 10. 2 22 447 30. 6 22. 2 1.0 23 578 32. 8 22. 2 24 478 34. 4 20. 6 26.9 25 600 32. 2 22. 8 26 597 33. 9 22. 2 27 571 33. 3 23.9 28 497 35. 0 23. 9 29 554 35. 0 23. 9 30 600 35. 0 23.9 98

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99 Table 12. Continued. Solar radiation Temperature ( C) Rainfall and Day (Langleys) Max. Min. irrigation (mm) 1 July 624 33. 9 23. 3 2 636 34.4 23.3 3 638 33.9 25. 0 4 294 28.3 23.9 3.3 5 430 31.1 23.9 6.4 6 258 27.8 21. 1 5.3 7 335 20.0 22.8 8.4 8 478 31.1 22. 2 1.2 9 609 31. 1 22.2 3.8 10 590 33.3 23.3 11 449 33.3 23 3 12 270 30.6 22.2 9.9 13 370 27.8 22. 3 .8 14 425 30.0 22.8 15 480 31.1 23.3 16 103 31. 1 23.3 37.6 17 392 30.6 22.8 8.4 18 485 30.0 23.3 10. 1 19 397 30.6 21 7 4.3 20 411 28.9 22. 2 3 21 519 32. 2 22. 2 .8 22 533 32.2 23.3 6.6 23 624 32. 2 23.3 24 628 32. 2 22.2 .3 25 583 33.9 22.8 2.0 26 337 30. 6 21. 7 1.3 27 454 31. 1 22. 8 77.5 28 220 27.8 23. 3 7,1 29 330 29.4 22. 8 9. 1 30 411 31.1 23.9 6.6 31 249 30.6 21.1 1 August 432 30.6 21. 1 82. 8 2 502 31 7 22. 2 11.9 3 614 31.7 21.1 4 514 31. 1 22. 2 5 478 30. 6 22.8 2.3 6 313 31 7 22.2 7 571 33. 3 21.7 8 311 30.0 23.9 .3 9 633 31.7 21.7 4.6 10 387 30.6 22.2 8 11 280 30. 0 22. 8 12. 2 12 342 31.7 23. 3 2.8 13 249 28.9 22.8 1.0 14 380 30. 0 22. 2 15 485 33.3 22. 8 50. 1

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100 Table 12. Continued Solar radiation Temperature ( C) Rainfall and Day (Langleys) Max. Min. irrigation (mm) 16 August 387 31.7 22 8 5 17 464 32 8 21.7 2 3 18 576 33 9 21.7 2 3 19 382 31 7 20 0 20 516 33 3 23 9 21 542 32 2 21.1 22 428 31.7 22 2 23 473 31.1 22 2 24 547 31.7 21.1 25 456 31.7 20 0 12.7 26 499 32 2 21.1 27 593 33 9 22 2 28 476 35 0 22 2 29 571 32 2 22 2 30 573 32 8 22.8 31 509 32.8 21.7 19 1 1 September 466 35 0 21.7 2 413 33 3 21.7 1 8 3 511 32 8 21.7 4 516 33.3 20 0 5 437 33 9 19.4 6 459 31 1 18.3 7 535 32.2 20 0 8 425 32.8 23 3 19 1 9 378 32.8 22 8 10 217 31.7 20 0 11 487 31 7 18 9 12 499 91 7 13 44Q 39 8 90 n 14 411 9 8 90 fi 1 Q 1 15 416 3 91 1 1 6 41 n o o o 90 R 1 7 ^9 S O ill O 9 n n 1 8 T 9 R 9n R Z U D ^ Q JL t-/ ^ o o o o o 1 R 1 1 O X ^ o o 10 9 i5
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LITERATURE CITED v-^n, H. N. 1976. Low light intensity at different stages of growth as affecting peanut yield components. M. S. thesis, Univ. Fla. 76 pp. Anonymous. 1977a. Ln Coop. Plant Pest Rep. 2:510. Anonymous. 1977b. In Coop. Plant Pest Rep. 2:563. Arant, F. S. 1948a. Status of velvetbean caterpillar control in Alabama. J. Econ. Entomol. 41:26-30. Arant. F. S. 1948b. Control of peanut insects. Ann. Rep. Ala. Expt Sta. 59:43-4. Arthur, B. W. L. L. Ilyche. and R. H. Mount. 1959. Control of the red-necked peanutworm on peanuts. J. Econ. Entomol. 52:468-70. Barfield, C. S., and J. W. Jones. 1979. Research needs for modeling pest management systems involving defoliators in agronomic crop systems. Fla. Entomol. 62:98-114, Bass, M. H. and F. S. Arant. 1973. Insect pests. Chapter XII. Pages 388-428. ^ Peanuts--culture and uses. Amer. Peanut Res. Ed. Assoc. Inc. 684 pp. Bass, M. H. and S. J. Johnson. 1978. Granulate cutworm: evaluation of insecticides for control. Agr. Exp. Sta. Auburn Univ. Leaflet 95. 3 pp. Bhagsari, A. S., and R. H. Brown. 1976. Photosynthesis in peanut ( Arachis ) genotypes. Peanut Sci. 3:1-5. Bissell T. L. 1941. A micro leaf worm on peanuts. J. Econ. Entomol. 35:104. Bliss, C. I., and R. A. Fisher. 1953. Fitting the negative binomial distribution to biological data. Biometrics 9: 176-200. Bliss, L. I., and A. R. G. Owen. 1958. Negative binomial distribution with a common K. Biometrika 45:37-58. 101

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102 Boote, K. J., J. W. Jones, G. 11. Smerage, C. S. Barfield, and R. D. Berger. 1980. Photosynthesis of peanut canopies as affected by leafspot and artificial defoliation. Agron. J. (in press)'. Bowes, G. W. L. Ogren and R. H. Ilageman. 1972. Light saturation, photosynthet ic rate, RuDP carboxylase: Activity and specific leaf weight in soybeans grown under different light intensities. Crop. Sci. 11: 77-9. Boyer, W. P., and W. A. Dumas. 1963. Soybean insect survey as used in Arkansas. U. S. Dept. Agric. Coop. Econ. Insect Report. 13:91-2. v^uschman, L. L.. W. H. Whitcomb, R. C. Hemenway D. L. Mays, Nguyen Ru N. C. Leppla, and B. J. Smittle. 1977. Predators of volvetbean caterpillar eggs in Florida soybeans. Env. Entomol. 6:403-7. Canerday, T. D. and F. S. Arant 1966. The looper complex in Alabama ( Lepidoptera Plusiinae) J. Econ. Entomol. 59:742-3. Cooper, C. S., and M. Quails. 1967. Morphology and chlorophyll content of shade and sun leaves of two legumes. Crop Sci. 7:672-3. Crocker, R. L. 1977. Components of the feeding niches of Geocoris spp. (Ilemiptcra: I.ygaeidae). Ph.D. dissertation. Univ. Fla. Ill pp. Dicke, F. F., and J. L. Jarvis. 1962. The habits and seasonal abundance of Orius insidiosus (Say) (HemipteraHeteroptera: Anthocoridae ) on corn. J. Kans Entomol. Soc. 35:339-44. Duncan, W. G. 1974. PENUTZ a simulation model for predicting growth, development and yield of a peanut plant. Amer. Peanut Res. Ed. Assoc. Proc. 6:72. Duncan, W. G. D. E. McCloud, R. L. McGraw, and K. J. Boote. 1978. Physiological aspects of peanut yield improvement. Crop Sci. 18:1015-20. Eden, W. G., C. A. Brogden and M. Sconyers. 1964. The granulate cutworm in peanuts and its control. Highl. Agr. Exp. Sta. Bull. 11:13. English, L. L. 1946. The velvetbean caterpillar on peanuts: control experiments. J. Econ. Entomol. 39: 531-3.

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103 Enyi, B. A. C. 1975. Effects of defoliation on growth and yield in groundnut ( Arachi s hypogea ) cowpeas (Vigna unguical ata ) soyabean ( Glycine max ) and green gram (Vigna aurens ) Ann. Appl Biol. 79:55-66. Fager, E. W. groups 1957. Determination and analysis of recurrent Ecology. 38:586-95. French, J. C. Georgia. 1973. Insect pest management on peanuts in J. Amer. Peanut Res. Ed. Assoc. 5:125-7. French, J. C. 1974, Georgia. Proc, Peanut insect pest management in Amer. Res. Ed. Assoc. 6:5-7. French, J. C. 1975, gram. J. Amer, A pilot insect pest management proPeanut Res. Ed. Assoc. 7:62-3. Gates, C. E., and F. G. Ethridge. 1972. A generalized set of discrete frequency distributions with FORTRAN program. Math. Geology. 4:1-24. Greene, G. L. and D. W. Gorbet 1973. Peanut yields following defoliation to assimilate insect damage. J. Amer. Peanut Res. Educ. Assoc. 5:141-2. —Hanson, W. D. R. C. Leffel, and Robert W. Howell. 1961. Genetic analysis of energy production in the soybean. Crop Sci. 1: 121-6. Hasse, W. L. 1971. Predaceous arthropods of Florida soybean fields. M. S. thesis. Univ. Fla. 67 pp. Henning, R. J., R. II. Brown, and D. A. Ashley. 1979. Effects of leaf position and plant age on photosynthesis and translocation. Peanut Sci. 6:49-50. Hoelscher, C. E. 1977. Managing insects on Texas peanuts. Tex. Agr. Ext. Serv. L-704. 8 pp. Huffman, F. R. 1974. Consumption of peanut foliage by the bollworm, Heliothis zea (Boddie) ( Lepidoptera : Noctuidae). M. S. thesis, Texas A & M Univ. 40 pp. Huffman, F. R. and J. W. Smith, Jr. 1979. Bollworm: peanut foliage consumption and larval development. Env. Entomol. 8:465-7. Janick, J., R. W. Schery F. W. Woods, and V. W. Ruttan. 1974. Plant Science. W. H. Freeman and Company. San Francisco. 740 pp.

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104 Johnson, M. W. R. E. Stinner, and R. L. Rabb. 1975. Ovipositional response of Ileliothis zea (Boddie) to its major hosts in North Carolina. Env. Entomol. 291-7. Kendall, M. G. and A. Stuart. 1961. The advanced theory of statistics, Vol. 3. Charles Griffin and Company, Ltd. London. 405 pp. Kimball, C. P. 1965. The Lepidoptera of Florida. An annotated checklist. Fla. Dept. Agri & Consumer Services, Div. Plant Industry, Arthropods of Florida and Neighboring Land Areas. 363 pp. King, D. R., J. A. Harding, and B. C. Langley. 1961. Peanut insects in Texas. Tex. Agr. Exp. Sta. MP-550. 14 pp. Kogan, M. and D. Cope. 1974. Feeding and nutrition of insects associated with soybeans. 3. Food intake, utilization, and growth in the soybean looper, Pseudo plusia includens Ann. Entomol. Soc. Amer. 67:66-72. Kuehl, R. 0., and R. E. Fye. 1972. An analysis of the sampling distributions of cotton insects in Arizona. J. Econ. Entomol. 65:857-60. Leuck, D. B. R. 0. Hammons L. W. Morgan, and J. E. Harvey. 1967. Insect preference for peanut varieties. J. Econ. Entomol. 60:1546-9. Linker, II. M., and F. A. Johnson. 1978. Tri-Statcs pest management project in Florida. Pages 25-9. l_n Proc. Nat. Pest Management Workshop. 220 pp. Malagamba, J. P. 1976. Plant density relationships in peanuts ( Arachis hypogaea L.) Ph.D. dissertation. Univ. Fla. 104 pp. Mangold, J. R., D. A. Nickle, and S. L. Poe. 1977. Populations of pests and their natural enemies in Florida peanuts. Proc. Amer. Peanut Res. Ed. Assoc. 9: 70. Martin, P. B. 1976. Cabbage looper, soybean looper, and tobacco budworm populations near Quincy Florida: Seasonal abundance, host preference, and suppression by natural enemies. Ph.D. dissertation. Univ. Fla. 255 pp. McCloud, D. E. 1974. Growth analysis of high yielding peanuts. Soil Crop Sci Soc. Fla. 33:24-6.

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105 McGill, J. F. R. J. Kenning, J. C. French, and S. S. Thompson. 1974. Growing peanuts in Georgia. Coop. Ext. Serv. Univ. Ga. Bull. 640. 46 pp. McGraw, R. L. 1977. Yield dynamics of Florunner peanuts ( Arachis hypogaea L.) M. S. thesis, Univ. Fla. 38 pp. Menke, W. W., and G. L. Greene. 1976. Experimental validation of a pest management mode. Fla. Entomol. 2:13542. Morgan, L. W. 1979. Economic thresholds of Heliothis species in peanuts. Pages 71-4. In Economic thresholds and sampling of Heliothis species on cotton, corn, and other host plants. Southern Coop. Ser. Bull. 231. 159 pp. Morgan, L. W. and J. C. French. 1971. Granulate cutworm control in peanuts in Georgia. J. Econ. Entomol. 64: 937-9. Neal, T. M. 1974. Predaceous arthropods in the Florida soybean agroecosystem M. S. thesis. Univ. Fla. 196 pp. Nickerson, J. C, C. A. Ralph Kay, L. L. Buschman and W. H. Whitcomb. 1977. The prosonco of Spissi s t ilus f estivus as a factor affecting egg predation by ants in soybeans. Fla. Entomol. 60:193-9. Nickle, D. A. 1977. The peanut agroecosystem in central Florida: Economic thresholds for defoliating noctuids (Lepidoptera Noctuidae) ; associated parasites; hyperparasitism of the Apanteles complex ( Hymenoptera Braconidae). Ph.D. dissertation. Univ. Fla. 131 pp. Pallas, J. E., Jr., and Y. B. Samish. 1974. Photosynthetic response of peanut. Crop Sci. 14:478-82. Pearce, R. B., G. E. Carlson, D. K. Barnes, R. H. Hart, and C. H. Hanson. 1969. Specific leaf weight and photosynthesis in alfalfa. Crop Sci. 9:423-6. v-'^enning de Vries, F. W. T. 1974. Substrate utilization and respiration in relation to growth and maintenance in higher plants. Neth. J. Agr. Sci. 22:40-4. Pieters, E., and W. L. Sterling. 1974. Aggregation indices of cotton arthropods in Texas. Env. Entomol. 3:598-600. Price, J. F. and M. Shepard. 1978. Calosoma sayi and Rabidura predation on noctuid prey in soybeans and locomotor activity. Env. Entomol. 7:653-6.

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iU6 Radford, P. J. 1967. Growth analysis formulae — their use and abuse. Crop Sci. 7:171-5. Rudd, W. G. W. G. Ruesink, L. 0. Newson D. C. Ilerzog, R. L. Jenson, and N. F. Marsolan. 1979. The systems approach to research and decision-making for soybean pest control. In New Technology of Pest Control (C. B. Huffaker, Ed.). John Wiley & Sons, Inc. New York ( in press) Schlinger, E. I., R. Van den Bosch, and E. J. Dietrick. 1959. Biological notes on the predaceous earwig Rabidura riparia (Pallas), a recent immigrant to California (Dermaptera: Labiduridae ) J. Econ. Entomol. 52:247-9. Sears, D. E., and J. W. Smith, Jr. 1975. A natural mortality table for corn earworm on peanuts. Tex. Agric. Exp. Sta. Prog. Report. 7 pp. Shepard, M., and G. R. Garner. 1976. Distribution of insects in soybean fields. Can, Entomol. 108:767-71, Shepard, M., G. R. Garner, and S. G. Turnipseed. 1977. Colonization and resurgence of insect pests of soybean in response to insecticides and field isolation. Env. Entomol. 6:501-6. Shibles, R. M., and C. R. Weber. 1965. Leaf area, solar radiation interception and dry matter production by soybeans. Crop Sci. 6:55-9. Smith, B. W. 1954. Arachis hypogaea reproductive efficiency. Amer. J. Bot 41:607-16. Smith. J. W. and C. E. Hoelscher. 1975. Insect pests and their control. Pages 68-73. Iji Peanut production in Texas. Tex. Agric. Exp. Sta. RM 3, Smith, J. W., and P. W. Jackson. 1976. Effects of insecticidal placement on non-target arthropods in the peanut ecosystem. Peanut Sci. 3:87-90. Smith, J. W., Jr., and D. G. Kostka. 1975. Modeling foliage consuming lopidoptera on peanuts. Amer. Peanut Res. Ed. Assoc. Proc. 7:66, Snow, J. W. and P. S. Callahan. 1968. Biological and morphologica]. studies of the granulate cutworm, Feltia subterranea (F. ) in Georgia and Louisisna. Ga. Agr Exp. Sta. Res. Bull. 42. 23 pp.

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107 Southwood, T. R. E. 1978. Ecological methods. Halsted Press, New York. 524 pp. Stinncr, R. E., J. R. Bradley, Jr., S. II. Roach, A. W. Ilartstack, and C. G. Lincoln. 1979. Sampling Ileliothis species on native hosts and field crops other than cotton. Pages 146-151. ]m Economic thresholds and sampling of Hel iothis species on cotton, corn, and other host plants. Southern Coop. Series Bull. No. 231. 159 pp. Strayer, J. R. 1973. Economic threshold studies and sequential sampling for management of the velvetbean caterpillar. Ant icarsia gemmatalis Ilubner, on soybean. Ph.D. dissertation. Clemson Univ. 87 pp. Thomas, G. D., D. B. Smith, and C. M. Ignoffo. 1979. Economic thresholds Iri Introduction to crop protection. Holt, Rinehart and Winston, Inc., New York. Tietz, H. G. 1972. An index to the described life histories, early stages and hosts of the macrolepidoptera of the continental United States and Canada. Allyn Mus Ent., Sarasota. 2 Vol. Trachtenberg, C. H., and D. E. McCloud. 1976. Net photosynthesis of peanut leaves at varying light intensities and leaf ages. Proc. Soil Crop Sci Soc. Fla. 35:54-5. Travis, P. A. 1977. Population dynamics of Labidura riparia (Pallas) (Dermaptera: Labiduridae ) M. S. thesis, Univ. Fla. 86 pp. USDA. 1977. Field crop summary 1976. Field crop and livestock reporting service. Florida Agr. Statistics. 9 pp. van den Bosch, R. and K. S. Hagen. 1966. Predaceous and parasitic arthropods in California cotton fields. Calif. Agric. Exp. Stn. Bull. 830. 31 pp. Wall, R. and R. C. Berberet. 1975. Parasitoids associated with lepidopterous pests on peanuts; Oklahoma fauna. Env. Entomol. 4:877-82. Wall, R. G. and R. C. Berberet. 1979. Reduction in leaf area of Spanish peanuts by the rednecked peanutworm. J. Econ. Entomol. (in review). Walton, R. R. and R. S. Matlock. 1959. A progress report of studies of the red-necked peanutworm in Oklahoma 1957 and 1958. Okla. State Univ. Exp. Sta. Proc. Series. P-320. 7 pp.

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1U8 Waters, W. E. 1955. Sequential sampling in forest insect surveys. For. Sci. 1:68-79. Waters, W. E. and W. R. Henson. 1959. Some sampling attributes of the negative binomial distribution with special reference to forest insects. Forest Sci. 5:397-412. Watt, K. E. F. 1968. Important ecological processes. In Ecology and resource management, McGraw-Hill, N7 Y. 450 pp. Whitcomb, W. H. 1974. Natural populations of entomophagous arthropods and their effect on the agroecosystem Pages 150-69. In Proceedings of the summer institute on biologicaT~control of plant insects and diseases. Univ. Press of Miss. 647 pp. Whitcomb, W. H., and K. Bell. 1964. Predaceous insects, spiders, and mites of Arkansas cotton fields. Ark. Agric. Exp. Sta. Bull. 690. 84 pp. Whitcomb, W. H. H. A. Denmark, A. P. Bhatkar, and G. L. Greene. 1972. Preliminary studies on the ants of Florida soybean fields. Fla. Entomol. 55:129-42. Williams, J. II., J. H. H. Wilson, and G. C. Bate. 1976. The influence of defoliation and pod removal on growth and dry matter distribution in groundnuts ( Arachis hypogaea L. cv Makula Red). Rhod. J. Agric. Res. 14: 111-17. Wolf, D. D. and R. E. Blaser. 1972. Growth rate and physiology of alfalfa as influenced by canopy and light. Crop Sci. 12:23-6. Young, J. H. F. R. Cox, and C. K. Martin. 1979. A peanut growth and development model. Peanut Sci. 6:27-36.

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BIOGRAPHICAL SKETCH The author was born on October 23, 1951, in Seminole, Florida. Upon graduation from Seminole High School in 1969, he entered the University of Florida. In June 1974 he received the degree of Bachelor of Science with Honors in Zoology. In the fall of 1974 he enrolled as a graduate student in the Department of Entomology and Nematology, College of Agriculture, at the University of Florida, receiving the Master of Science degree in June, 1976. He enrolled in the Department of Entomology and Nematology at the University of Florida during the summer 1976, and has pursued work toward the degree of Doctor of Philosophy. He is currently a member of the Entomological Society of America and the Florida Entomological Society. 109

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I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy.' S. L. Poe, Chairman Professor of Entomology I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. W.'^Jones ssociate Professor of Agricultural Engineering I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. D. H. Habeck Professor of Entomology

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I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. C. A. Musgrave' Assistant Professor of Entomology This dissertation was submitted to the Graduate Faculty of the College of Agriculture and to the Graduate Council, and was accepted as partial fulfillment of the requirements for the degree of Doctor of Philosophy. December 1979 Dean, Graduate School