Group Title: Research report - North Florida Research and Education Center ; 87-14
Title: Population dynamics of insect predators in relation to tillage and subsoiling prior to planting soybeans
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 Material Information
Title: Population dynamics of insect predators in relation to tillage and subsoiling prior to planting soybeans
Series Title: Research report (North Florida Research and Education Center (Quincy, Fla.))
Physical Description: 17 p. : ill. ; 28 cm.
Language: English
Creator: Funderburk, J. E ( Joseph E. ), 1954-
Wright, D. L ( David L )
Teare, I. D ( Iwan Dale ), 1931-
North Florida Research and Education Center (Quincy, Fla.)
Publisher: North Florida Experiment Station
Place of Publication: Quincy Fla
Publication Date: 1987
 Subjects
Subject: Insect population density   ( lcsh )
Florida   ( lcsh )
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references.
Statement of Responsibility: by J.E. Funderburk, D.L. Wright and I. D. Teare.
General Note: Caption title.
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Bibliographic ID: UF00066067
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 71126648

Full Text
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6 7- /"y
Population Dynamics of Insect Predators In Relation to
Tillage and Subsoiling Prior to Planting Soybeans/

J. E. Funderburk, D. L. Wright, and I. D. Teare2/

ABSTRACT

Bigeyed bugs (Geocoris spp.) and damsel bugs (Nabis and Reduviolus spp.)

are common polyphagous beneficial insect predators in many crops. The object-
ive of this research was to measure the effects of tillage and subsoiling

regimes on population dynamics and population size of beneficial predators to

aid in development of cultural IPM strategies for biological control of insect

pests in a wheat/soybean sequential cropping system. Bigeyed bug nymphal and

adult population dynamics were similar in each tillage/subsoiling treatment

except that there was considerable overlap of generations in 1986 which was

not observed in 1985. Disk tillage had greater bigeyed bug nymphal and adult

population sizes than no tillage in 1985 and 1986, while subsoiling did not

influence population size. Damsel bug population dynamics were very similar

in each tillage/subsoiling treatment in 1985 and 1986. Population sizes of

adult and nymphal damsel bugs in 1985 were less in no tillage without subsoil-

ing than in disk tillage without subsoiling, disk tillage with subsoiling and

no tillage with subsoiling, which had similar population sizes. Population

sizes were similar in all treatments in 1986.

Additional index words: Bigeyed bug, Geocoris spp., damsel bug, Nabis spp.,

Reduviolus spp., disk tillage, no tillage, subsoiling.


!/Contribution from the Inst. of Food and Agric. Sci., Florida Exp. Stn.,

Univ. of Florida and the North Florida Res. and Educ. Ctr., Quincy, FL

32351. Research Report NF 87-14.
!/Assistant Professor of Entomology, Professor of Agronomy, and Research

Scholar/Scientist of Agronomy, Univ. of Florida. Central Science
Library

SEP 29 1987

University of Florida









INTRODUCTION

Geocoris spp. (bigeyed bugs) and Nabis and Reduviolus spp. (damsel bugs)

are common, polyphagous insect predators in many crops. In the Southeast,

populations of Geocoris punctipes (Say) occur in large numbers in soybean

fields in the southern U.S. (Shepard et al. 1974). R. rosepiennis Reuter is

the most common species of damsel bug comprising over 90% of all individuals

occurring in a soybean field (Dietz et al. 1976). Other Nabidae that occur in

soybean in the region are N. alternatus Parshley, N. americoferus Carayon, N.

capsiformis Germar, and N. deceptivus Harris. Adults and nymphs both genus

feed on eggs and almost any soft-bodied arthropod. The arthropod diet is

supplemented by some feeding on plants which improves survival and decreases

developmental time (Naranjo and Stimac, 1985), but the plants suffer no damage

(Ridgway and Jones, 1968). Damsel bugs and bigeyed bugs are important

predators of many economically important soybean pests. Bigeyed bugs are

predators of Anticarsia gemmatalis Hubner (Elvin et al., 1983), Nezara viri-

dula (L.) (Crocker and Whitcomb 1980), Heliothis zea Boddie (Whitcomb and Bell

1964), H. virescens, (F.) (McDaniel and Sterling 1979), and Pseudoplusia

includes (Walker) (Richman et al. 1980). Damsel bugs are important predators

of Anticarsia gemmatalis Hubner (Buschman et al. 1977), Heliothis spp.

(McCarty et al. 1980), and Plathypena scabra (F.) (Sloderbeck and Yeargan

1983).

The population dynamics of bigeyed bugs and damsel bugs in conventionally

tilled soybean fields has been elucidated for the southern U.S. and other

growing regions. Bigeyed bug numbers were greatest in late August to early

September in Kentucky (Raney and Yeargan 1977), early August or mid-September

in North Carolina (Deitz et al. 1976), late September in South Carolina

(Shepard et al. 1974a), and between late June and early August in Mississippi

(Pitre et al. 1978). In Florida and Alabama bigeyed bugs were present during









most of the growing season, with three complete and additional partial gener-

ations being typical (Funderburk and Mack 1987). The number of bigeyed bugs

increased through the growing season, with numbers usually greatest near the

end of the growing season. Damsel bug numbers were greatest near mid-season

in Kentucky (Raney and Yeargan, 1977), Mississippi (Pitre et al., 1978), and

Brazil (Correa et al., 1977) and late in the season in South Carolina (Shepard

et al., 1974b) and North Carolina (Deitz et al., 1976). Two to four complete

and additional partial generations appear typical in soybean, with the number

of generations developing in individual fields dependant on the date of first

appearance of adults (Mack and Funderburk 1987).

Much research obviously has demonstrated that bigeyed bugs and damsel bugs

are abundant, indigenous naturalenemies, with their numbers increasing along

with the pests and reaching greatest numbers during mid- or late-season.

Enhancement and conservation of beneficial predators is a major priority in

soybean IPM programs. For example, insecticides used to control the pests may

also kill the beneficial predators. If this happens the pest frequently rein-

vades the field at a faster rate than the beneficial. Pest numbers then

build up rapidly because there are few beneficial predators left to hold down

the pest populations. IPM strategies in soybean therefore are designed to use

insecticides only when pest populations reach economic numbers and to select-

ively use insecticides in ways that reduce pest populations, but have the

least negative impact on populations of these predators.

Tillage operations modify soil habitats where many pest and natural

enemies reside during at least part of their life cycle. These modifications

can alter survival or development. Herzog and Funderburk (1986) discussed the

ways that tillage influences the biology of specific pests and natural

enemies. They concluded from a review of the literature that most soybean

pests and their natural enemies whose populations have been quantified in









tillage studies are affected by soil tillage practices. Numerous agronomic-

ally acceptable tillage and subsoiling regimens have been developed for

soybean production systems in the southeastern U.S. A knowledge of the

effects of these tillage and subsoiling regimes on pest and natural enemy

biology would aid development of cultural control strategies in soybean IPM

programs. It may be possible to select tillage/subsoiling production systems

that optimize the benefits of biological control by bigeyed bugs and damsel

bugs, thereby minimizing the need for insecticidal control.

Damsel bugs overwinter in grassy ground covers, and during the summer

prefer shady habitats such as those found in soybean fields. The bigeyed bugs

overwinter in low-growing grasses and ground trash (Sprenkel, 1983). Conser-

vation tillage systems have an effect on ground cover and ground trash, and

may affect damsel bug and bigeyed bug biology through modification of ground

litter and other ways. In Virginia, McPherson et al. (1982) reported that

Nabis spp. and Geocoris spp. were more numerous in conventional and drill-

planted soybean fields than in the double-cropped, late-planted soybeans

during the bean filling period when most insect-related crop damage occurs.

Troxclair and Boethel (1984) compared damsel bug and bigeyed bug populations

in preplant-disked and no-till soybean tillage regimes, but results were

inconclusive. Poor precision was undoubtedly a problem due to the choice of

sweep-netting as the sampling method (e.g., Irwin and Shepard, 1980). They

emphasized the importance of understanding the effects of tillage on bigeyed

bug and damsel bug populations and urged further research. No other research

has been conducted to elucidate the effects of tillage and subsoiling on

bigeyed bug and damsel bug population dynamics.

Musick (1985) and Herzog and Funderburk (1986) have concluded that each

crop and pest situation must be evaluated individually and independent judg-

ments made for each specific geographical location. Therefore, the primary









purpose of the present study was to determine the effect of tillage and sub-

soiling on the population dynamics and population sizes of bigeyed bugs and

damsel bugs in the subsequent soybean crop. Such information will allow for

implementation of pest management practices that conserve the natural enemies

in soybean fields produced in a wheat/soybean sequential-cropping system in

the southeastern U.S.

MATERIALS AND METHODS

Cobb soybean [Glycine max (L.) Merr.] was planted July 3, 1985 and Kirby

soybean was planted June 12, 1986 following wheat harvest each year on a

Norfolk sandy loam (fine-loamy siliceous, thermal Typic Paleudult) at Quincy,

FL. The divergent planting dates were used to determine if population numbers

of bigeyed bugs and damsel bugs were affected by time of planting in Florida

as described by McPherson, et al. (1982). Plot size for each treatment was

7.6 x 15.2 x in 1985 and 7.6 x 24.4 m in 1986. Tillage and subsoil treatments

are described in Table 1.



Table 1. Description of tillage and subsoil treatment and equipment used.


Treatment
Code Name Equipment Used

DT Disk Tillage* Disk + Cone planter**
DTSS DT plus in subsoilt(SS) Disk + Cone planter
+ Subsoiler
NT No Till Cone Planter
NTSS NT plus SS Cone planter + Subsoiler


*Gang disk in two directions.
**Almaco 2-row cone planter.
tSubsoiling with chisel plow at depth of 0.23 m.



Soybean planting rate was 45 kg ha1. Rainfall in 1985 required no

soybean irrigation. In 1986, the field received a preplant irrigation of 10









mm water ha Subsequent irrigations were administered when tensiometers

placed at 0.15 m depth reached 0.2 Mg Pa.

Herbicide treatment in 1985 consisted of broadcast sprayed Poast 2-[ethox-

yimino)butyl]-5-[2-ethylth-3-hydroxy-2-cyclohexen-l-one at 0.584 1 ha~- + Bas-

agran3-( 1-Methyl-ethyl)-(H-2,1,3-benzothiadiazin-4 (3H)-one2,2-dioxide at 1.753

1 ha-1 + Paraquat 1,1'-Dimethyl-4,4'- bipyridiniumion; present as the dichlor-

ide salt (ICI/Chevron/Crystal) or dimethyl sulfate salt at 1.169 1 ha- + crop

oil at 2.378 1 ha- on July 31. A second herbicide treatment of Paraquat at

0.584 1 ha-1 + 2,4-DB 4-(2,4-Dichlorophenoxy)butyric acid at 1.169 1 ha~1 + X-

77 at 0.227 1 per 379 1 of solution was applied on Sept. 5.

The initial 1986 herbicide treatment was a tank mix broadcast sprayed

application of Sencor DF 4-Amino-6-(l,l- dimethylethyl)-3-(methylthio)-1,2,4-

triazin-5(4H)-one at 0.56 kg ha1 + Surflan 3,5- Dinitro-N4 ,N4-dipropylsul-

fail-amide at 1.753 1 ha~- + paraquat at 1.753 1 ha-1 + X-77 at 0.227 1 per

379 1 of solution. A second herbicide treatment was a directed spray of Fusi-

lade butyl(RS)-2-[ 4-[ 5-( tri-fluoromethyl) -2-pyuridinyl] oxy]phenoxy]propanoate

at 3.507 1 ha1 + X-77 at 0.229 1 per 400 1 of solution applied on July 22.

The fields were not treated with an insecticide.

Nymphal and adult population density was estimated at 6 dates during the

1985 season (8-23, 9-4, 9-16, 9-28, 10-9, 11-6) and at 5 dates during the 1986

season (7-3, 7-15, 7-29, 8-12, 8-28). The sixth sampling date in 1986 was

discontinued because of excessive lodging caused by heavy rains and high

winds. Sampling was begun at early vegetative stage and continued to the late

seed stage of crop growth.

Sampling procedures were according to those established in a review of

previous studies, Irwin and Shepard (1980), as being most appropriate for

estimating their nymphal and adult populations in soybean. The ground cloth









method was employed, 1.8-m samples were taken in each plot on each sample

date. For each sample, the ground cloth was laid between two rows, the

soybean plants from both sides (0.9 m on each side) beaten onto the cloth, and

the number of nymphs and adults determined. Also, bases of the plants and

adjacent soil were examined for any bigeyed bugs and damsel bugs.

The experimental field design was a completely randomized block with four

replications. The statistical analysis was a split plot with date as the

whole plot and treatments (tillage and subsoiling) as the subplots. Conserva-

tive degrees of freedom were used in the analyses as described by Weiner

(1971), because the effect of date was a repeated measure.

RESULTS AND DISCUSSION

Population dynamics of bigeyed bug are shown for each tillage/subsoiling

treatment in 1985 and 1986 (Fig. 1). Bigeyed bug populations of a partial

generation and then two complete generations occurred in the soybean plots in

1985 and populations of different generations did not overlap greatly. A few

adults of a partial generation were detected on the first sample date of 1985

during soybean growth stage V4 indicating that adult populations undoubtedly

had been greater earlier in the season. Nymphal populations declined and

adults of this generation were greatest during soybean growth stage R1.

Nymphal populations of the next bigeyed bug generation then occurred in the

soybean plots with sample estimates greatest during soybean growth stage R5.5.

This generation had sufficient time to complete development, because nymphal

population estimates became very low and adult population estimates were

greatest during soybean growth stage R7.

Population dynamics in the 1986 disk tillage with no subsoiling (DT), disk

tillage with subsoiling (DTSS), and no-till with no subsoiling (NT) treatments

were similar to the 1985 population dynamics of bigeyed bugs in all treatments









(Fig. 1) with considerable overlap between bigeyed bug generations. However,

bigeyed bug populations appeared later in the season in the no tillage with

subsoiling (NTSS) treatment, and population estimates were much lower (Fig.

1). Only one, and possibly two, partial generations occurred. Adults of a

partial generation were evident during soybean growth stages V10 to V11.

Nymphal populations soon developed, with population estimates increasing

greatly from soybean growth stages V10 to V11. Sample estimates of adult

populations declined somewhat from V10 to Vll and R2, but not greatly. Adults

from the next generation then occurred, and sample estimates of adults

increased in two of the treatments (DT and DTSS) during soybean growth stage

R4. Nymphal populations of the next generation also were present in the

soybean plots during soybean growth stage R4. This last generation undoubted-

ly completed development in the soybean plots over the last part of the

growing season when sample estimates were not obtained.

Population size was affected by tillage/subsoiling treatment. Treatment

differences were significant in 1985 and 1986 for nymphs (F1,1, = 3.92 and

F,15 = 6.71, respectively; P < 0.05 and 0.01, respectively). The orthogonal
treatment comparisons revealed that the treatment differences were mostly due

to the tillage practice employed. The DT and DTSS plots had greater bigeyed

bug numbers than the NT and NTSS plots in 1985 and 1986 (F,18 = 7.27 and

F1,1s = 17.2, respectively; P < 0.05 and 0.01, respectively). Subsoiling did
not substantially influence bigeyed bug nymphal populations. Numbers were

statistically similar in the NTSS and NT plots in 1985 (F ,1s = 2.10), but the

difference in 1986 approached the 0.05 level of significance (F1,18 = 4.38).

Numbers were very similar in the DTSS and the DT plots in 1985 and 1986 (F
-1 18
= 0.30 and F1, s = 0.86, respectively). There was no date*treatment inter-

action in 1985 or 1986 (F,8 = 1.43 and F = 1.55, respectively).









Adult population estimates in 1985 usually were greater in the DT and DTSS

plots than in the NT and NTSS plots. However, there were no significant

treatment differences (F1,18 = 1.34). Treatment differences of adult popula-

tion size just failed to be significant in 1986 (F 1 = 2.59; P = 0.06).

Orthogonal comparisons revealed that adult treatment differences, as with

nymphal populations, were mostly attributable to tillage practice. The DT

plots had greater numbers bigeyed bug nymphs than the NT plots (F1, 1 = 4.25;

approaches 0.05 level of significance). Subsoiling did not influence adult

populations of bigeyed bugs. Numbers were similar in the NTSS and NT plots

(F 1,s = 0.03) and in the DTSS and the DT plots (Fi,15 = 3.55). There was no
date*treatment interaction for adults in 1985 or 1986 (F 0.60 and F
5,18 -4,15
= 1.05, respectively).

Population dynamics of damsel bugs were very similar in each tillage/sub-

soiling treatment in 1985 and 1986 (Fig. 2). One complete and a partial

generation developed in the soybean plots in 1985. There was little overlap

in populations of different generations. Adults of a partial generation were

present between soybean growth stages V4 to R4, with population estimates

greatest during soybean growth stage R1. Nymphal populations developed and

were greatest during soybean growth stage R5.5. This generation completed

development, and nymphal population estimates were very small and adult popu-

lation estimates large during soybean growth stage R7. In 1986, one complete

and a partial generation developed in each tillage/subsoiling treatment.

Adults of a partial generation were present between soybean growth stages V4

and V11. Nymphal population estimates were substantial during soybean growth

stage R2 and became greater during soybean growth stage R4. This generation

probably completed development during the remainder of the growing season when

sampling was discontinued. Adults of this generation were present on samples

taken









during soybean growth stage R4. It is probable that sufficient time was

present for another partial damsel bug generation to be present in the soybean

plots during the growing season, but no data was collected.

Population size of adult damsel bugs was significantly affected by

tillage/subsoiling treatment in 1985 (F1,1 = 6.13, P < 0.05). Orthogonal

treatment comparisons revealed that the NT plots had fewer adults than plots

of all other treatments (FI18 = 10.3, P < 0.01). Adult numbers in the NTSS

plots were similar to numbers in plots of DT and DTSS treatments (F1,1 =

1.79), which also had similar population sizes (F Ig1 = 0.34). There were no

significant treatment differences in nymphal populations in 1985 (F,18 =

2.00), but population size was much less in the NT plots than in plots of the

other treatments during soybean growth stage R5.5 when nymphal population

estimates during the growing season were greatest. Nymphal population esti-

mates in all treatments were very low on nearly all other sample dates. Adult

and nymphal population estimates in 1986 were similar in each tillage/subsoil-

ing treatment (FI, 1 = 0.42 and 0.28, respectively). The date*treatment

interaction was not significant for nymphs or adults in 1985 (Fs,18 = 1.79 and

0.82, respectively) and 1986 (F 4,1 = 0.76 and 0.46, respectively).

Tillage and subsoiling practices in our study did not greatly affect popu-

lation dynamics of bigeyed bugs and damsel bugs. Population trends were

always similar for damsel bugs. One complete and an additional partial gener-

ation occurred in each tillage/subsoiling treatment in both years. Two com-

plete and additional partial generations of bigeyed bugs were typical in the

soybean plots, although only one complete generation apparently occurred in

one treatment in one year. Two to four complete and additional partial gener-

ations of damsel bugs and three to four complete and additional partial gener-

ations of bigeyed bugs are typical for full-season soybean in this region









(Mack and Funderburk 1987, Funderburk and Mack 1987). Our data would indicate

that fewer generations of both occur in soybean doublecropped with winter

wheat. The growing season is shorter, leaving less time for more generations

to develop.

Tillage affected the number of bigeyed bugs in soybean in our studies.

Population size through the growing season was less in no tillage than in disk

tillage soybean. Tillage had less affect on damsel bug populations. No

tillage soybeans subsoiling in one year had lower population size than DT,

DTSS and NTSS soybean, but in the other year population size was similar in

all treatments. These findings for bigeyed bugs and damsel bugs corroborate

previous investigations by McPherson et al. (1982) and Troxclair and Boethel

(1984) and provide strong evidence that tillage practices affect populations

of these important indigenous predators in soybean. McPherson et al. (1982)

hypothesized that differences in bigeyed bug numbers between disk tillage and

no tillage soybean in their studies were related to differences in planting

dates. Planting date was the same for each treatment in our experiments. The

planting date between years was very different. Consequently, tillage, and

not planting date, was responsible for the treatment differences in our

studies. Subsoiling did not affect bigeyed bug numbers. Subsoiling did

affect damsel bug populations, with subsoiling increasing population size in

instances where their populations were reduced in no tillage soybean.

Our studies show that tillage is a production practice which can be modi-

fied in integrated pest management programs of soybean to enhance populations

of the most common above-ground predators of foliar pests. It should be safe

to assume that the amount of predation is a function of predator population

size. If so, biological control by these most important above-ground

predators would be greater in soybean produced by disk tillage than by no









tillage. There is not an adequate understanding of the effects of tillage and

subsoiling on pest populations. These production practices could affect the

biologies of pests in ways unrelated to effects on bigeyed bugs and damsel

bugs. Such an understanding is especially needed for soybean produced in the

southeastern U.S., where pest losses are great. Modification of tillage and

other production practices should prove an efficient way of increasing the

amount of biological control to soybean pests and of alleviating the need for

other, less desirable control tactics.










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V4 RI R4 R5 R5,5 R7 V4 VIOVII R2 R4


2_5`.` '--.. __ I I i-- "-'- ...U
255 275 295 310 184 204 224 240
1985- DAY OF YEAR -1986
Number of bigeyed bugs in relation to day of year (Days Julian for
1985 and 1986) and physiological stage of development. Solid line
- disc tillage, dashed line no tillage, O subsoiled, A not


subsoiled.


Figure 1.






V4 RI R4 R5R5.5


1985 DAY OF Y


EAR 1986


Number of damsel bugs in relation to day of year and physiological


stage of development.


Figure 2.


R7


V4 VIO VII


R2 R4




























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