Group Title: Research report (North Florida Research and Education Center (Quincy, Fla.))
Title: Seasonal abundance and dispersion patterns of damsel bugs (hemiptera Nabidae) in Alabama and Florida soybean fields
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 Material Information
Title: Seasonal abundance and dispersion patterns of damsel bugs (hemiptera Nabidae) in Alabama and Florida soybean fields
Series Title: Research report (North Florida Research and Education Center (Quincy, Fla.))
Physical Description: 13 p. : ; 28 cm.
Language: English
Creator: Mack, T. P
Funderburk, J. E ( Joseph E. ), 1954-
North Florida Research and Education Center (Quincy, Fla.)
Publisher: North Florda Research and Education Center
Place of Publication: Quincy Fla
Publication Date: 1987
 Subjects
Subject: Grasses -- Varieties -- Florida   ( lcsh )
Forage plants -- Varieties -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (p. 11-13).
Statement of Responsibility: T.P. Mack and J.E. Funderburk.
General Note: Caption title.
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Bibliographic ID: UF00066065
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 71069260

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A//75 S

Seasonal Abundance and Dispersion Patterns of Damsel Bugs

(Hemiptera: Nabidae) in Alabama and Florida Soybeaeno%91$nc

T. P. Mack and J. E. Funderburk library

SEP 23 1987

ABSTRACT / U versty of Florida
Seasonal abundance and dispersion characteristics oF

and nymphal Nabidae (damsel bug) populations were determined for

soybean fields located in Alabama and Florida. Populations were

present in each field from late June or July until the end of the

growing season. The number of generations depended on the date

of first appearance of adults, with two to four complete

generations developing and with additional partial generations

also present. Populations of different generations were broadly

overlapping. The variance/mean ratio and Taylor's power law were

calculated for adult and nymphal sample estimates. Nymphs were

aggregated and adults were slightly aggregated to random.


Additional index words: Glycine max (L.) Merri., Reduviolus

roseipennis Reuter, Nabis alternatus.






IContribution 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 87-10.
2Professor of Agronomy, Auburn Univ. 36849-4201 and Assistant

Professor of Entomology, Univ. of Florida.









Nabis and Reduviolus spp. (damsel bugs) are important preda-

tors in soybean fields throughout the U.S. In the Southeast, R.

roseipennis Reuter is the most common species, comprising over

90% of all individuals occurring in a soybean field (Turnipseed

1974, 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 feed on many species of soft-bodied arthropods and will

feed on insect eggs. The prey diet is supplemented with some

feeding on plants, but the plants suffer no damage (Ridgway and

Jones 1968). Damsel bugs are important predators in soybean of

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

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

Yeargan 1983), and others.

The seasonal abundance of damsel bugs in soybean varies with

geographical location. Density is greatest near midseason in

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

1978), and Brasil (Correa et al. 1977) and late in the season in

South Carolina (Shepard et al. 1974a) and North Carolina (Deitz

et al. 1976). More than one generation occurred in each case, as

populations were present during much of the growing season. No

published information exists on the population dynamics of damsel

bugs in soybean in more southerly areas of the soybean growing

region. Also, no comparisons have been made of their seasonal

abundance during the same growing season in fields located in

different areas of the same geographical region.









Information on the dispersion characteristics of damsel bugs

in soybean or other crops is scarce. Waddill et al. (1974)

reported that damsel bug populations were randomly distributed in

soybean, and Bechinski and Pedigo (1981) reported that nymphal

Nabis spp. populations were slightly aggregated and that adults

were randomly distributed. Dispersion characteristics of insect

populations have been found to vary with population density and

sample-unit size (Wilson and Room 1982, 1983). Additional

information taken over a range of population densities and at a

different sample-unit size from the previous studies is needed

before dispersion characteristics of their populations can be

understood.

The purpose of the present study was to determine the

seasonal abundance of damsel bug populations in soybean in

Alabama and Florida. Dispersion characteristics also were

calculated from this data which represented a range of population

densities and a different sample-unit size from the Waddill et

al. (1974) and Bechinski and Pedigo (1981) report. Such

information will allow for implementation of pest management

practices that conserve these natural enemies in soybean fields.

Materials and Methods

Damsel bug adult and nymphal populations were sampled during

1985 and 1986 in soybean fields located in Florida and Alabama.

All fields were at least 2 ha in area with none treated with an

insecticide that would directly affect damsel bug populations.

Tillage practices consisted of disking before planting, with no

subsoiling. Planting dates ranged from late May to early June.









All fields were located in Alabama in 1985, with one field each

in Dallas, Elmore, and Henry counties. Two fields were sampled

in 1986. One field was located in Dallas Co., Alabama and the

other in Gadsden Co., Florida. Soybean varieties were 'Tracey M'

for the Alabama fields and 'Braxton' for the Florida field.

The ground cloth method was used to sample nymphal and adult

populations in each soybean field (Rudd and Jensen 1977, Shepard

et al. 1974b, Turnipseed 1974). Forty-eight, 1.8-m samples were

taken in each field on each sample date when their populations

were in detectable numbers. 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 counted. Also, bases of the plants and

adjacent soil were examined for any damsel bugs.

The variance/mean ratio was calculated with Myers' FORTRAN

program for adult and nymphal counts on each sample date within

each field (Southwood 1978), with these analyses performed using

Myers' (1978) FORTRAN program. Log-transformed means and

variances of adult and nymphal sample counts were calculated for

each sample date within each field, and Taylor's (1984) power law

relationship determined for each field. A Taylor's power law

relationship also was determined by combining data from all

fields sampled in each year. All regression relationships were

determined with SAS programs (SAS Institute 1982a,b).

Results and Discussion

The numbers of adult and nymphal damsel bugs (x+SEM) in each

soybean field sampled in 1985 and 1986 are shown in Figs. 1 and









2, respectively. Variation between samples, based on the SE

values, was fairly large, which necessitated the large number of

samples taken. Adults were first detected in all fields during

June or July. Nymphs were detected in each field 1 to 2 weeks

later. Adult and nymphal populations then were common through

the remainder of the growing season.



40-
HENRY CO., AL
DALLAS CO., AL
w 30- ***"......ELMORE CO., AL
-------GADSDEN CO., FL

S20-


z 10- i1


.... ....... '' .. ---....--
0O-

6/18 6/28 7/8 7/18 7/28 8/7 8/17 8/27 9/6 9/16 9/2610/6
1985 SAMPLE DATE

Fig. 1. Numbers (x+SEM) of adult and nymphal damsel bugs in the
three soybean fields sampled in 1985 in Dallas, Elmore, and
Henry Cos., Alabama.






More than one complete generation occurred in each field.

Generational cycles are indicated by peaks in nymphal and adult

sample estimates that occurred ca. every 30-40 days (Figs. 1 and

2). The number of generations that occurred in individual fields









depended on the date of first appearance of adults. Four

complete generations occurred in the Elmore Co. and Dallas Co.,

Alabama fields during 1985, with additional partial generations

also present. Only two complete generations developed in the

Henry Co., Alabama field in 1985 and the Gadsden Co., Florida

field in 1986, because populations did not appear until late

July. There was considerable overlap between generations,

because the density of damsel bugs did not decline greatly once

populations had built up in a field.

50-
----- GADSDEN CO.,FL
r 40- DALLAS CO., AL
U-
S30-


20-
z
10-


Q^ _.-------- ----------- -.- -,------------ ---T -
6/13 7/3 7/23 8/12 9/1 9/21 10/11

1986 SAMPLE DATE

Fig. 2. Numbers (x+SEM) of adult and nymphal damsel bugs in the
two soybean fields sampled in 1986 in Dallas Co., Alabama and
Gadsden Co., Florida.



For each sample date in the 1985 and 1986 soybean fields, the

variance/mean ratio of nymphal and adult populations are present-

ed in Table 1. Variance/mean ratios of <1, 1, and >1 represent

uniform, random, and clumped distributions, respectively













(Southwood 1978).


According to this measure of dispersion,


populations of nymphs were aggregated on 69.2% of the field/date


data sets when data were sufficient for analysis. Adult


populations were aggregated 25.0% of the time.


Table 1. Variance/mean ratios for nymphal and adult damsel bug populations in

the 1985 and 1986 soybean fields in Dallas, Elmore, and Henry Cos.,

Alabama and Gadsden Co., Florida.


SAMPLE s_/x SAMPLE s2/x

DATE NYMPHS ADULTS DATE NYMPHS ADULTS


1985 HENRY CO., AL

AUG. 1.23

SEPT. 2.02*

SEPT. 2.25*

SEPT. 1.79*

1985 DALLAS CO., AL

JULY 1.16

JULY 1.89*

JULY 2.81*

AUG. 1.23

AUG. 1.23

AUG. 2.04*

AUG. 1.52*

SEPT. 1.61*

1986 DALLAS CO., AL

JULY

JULY 1.32

AUG. 1.47*

AUG. 1.76*

AUG. 1.10


14 JULY

28 JULY

4 AUG.

11 AUG.

18 AUG.

25 AUG.

2 SEPT.

8 SEPT.

17 SEPT.

24 SEPT.

3 OCT.


1.38*

1.07

0.86

1.06




1.23

2.09*

1.22

1.22

1.19

1.14

1.06



1.45*



1.28



1.16


JUNE

JUNE

JULY

JULY

JULY

JULY

AUG.

AUG.

AUG.

AUG.

AUG.

SEPT

SEPT


1986 GADSDEN CO., FL



1.22

1.35*

1.48*

1.51*

1.36*

1.53*

1.34*

2.34*

2.01*

0.89

1985 ELMORE CO., AL

1.64*

1.23

1.08

0.92

1.20

1.56*

1.45*

1.96*

2.52*

1.88*

1.34*

1.95*

1.56*


*Significantly > 1 (P < 0.05) by a X2 test


1.28

1.06

1.22

1.22

1.16

1.74*

1.33

0.94

1.62*

1.44

1.33


1.11

0.85

1.50*

0.89

1.50*

1.14

1.32

1.19

1.19

1.13

1.60*









Taylor's power law relates variance (s2) to mean density (m)

by the relationship, s = amb. Taylor et al. (1978) considered

the slope (b) to reflect dispersion characteristics for a

species, with values of b < 1, b = 1, and b > 1 indicating

uniform, random, and clumped distributions, respectively. The

intercept (a) was considered to reflect sample-unit size.

Taylor's power law allows for a description of a species

distribution pattern as changing with density.

Regression statistics of Taylor's power law relationships for

nymphal and adult damsel bug sample estimates for each soybean

field and for the three 1985 fields combined and the two 1986

fields combined are given in Table 2. For all relationships

involving nymphal sample estimates, b was statistically > 1 (P <

0.05) for a t test. These values of b and the high r2-values

(averages = 0.97 and 0.96 for 1985 and 1986, respectively) of the

Taylor's power law relationships indicate that populations were

aggregated over a wide range of population densities. For

relationships involving adult sample estimates, b was

statistically > 1 four out of seven times. The average r2-values

for 1985 and 1986 were 0.91 and 0.90, respectively. Thus,

precision was excellent. These values of b indicate that adult

populations were slightly aggregated to random.














Table 2. Regression statistics of Taylor's power law relationship for
nymphal and adult sample data in the 1985 and 1986 soybean
fields in Henry, Elmore, and Dallas Cos., Alabama and Gadsden
Co., Florida. (All relationships are significantly linear
beyond the 0.01 level and no intercept is significantly
different from 0 according to a t test).


NYMPHS ADULTS
FIELD AND YEAR INTERCEPT SLOPE r INTERCEPT SLOPE r




HENRY CO., AL 1985 -0.05 1.37* 0.97 -0.03 1.36* 0.91
ELMORE CO., AL 1985 0.00 1.48* 0.99 0.00 0.98 0.94
DALLAS CO., AL 1985 0.00 1.36* 0.96 0.00 1.24 0.89
ALL FIELDS, 1985 0.00 1.33* 0.97 0.00 1.19* 0.92
DALLAS CO., AL 1986 0.00 1.26* 0.97 0.01 0.90 0.84
GADSDEN CO., FL 1986 -0.03 1.37* 0.95 0.00 1.27* 0.96
ALL FIELDS 1986 -0.02 1.36* 0.96 0.00 1.22* 0.93


*Significantly > 1 (P < 0.05) according to a t test




Damsel bugs were present in the soybean fields sampled in our

study from late June or July until sampling was discontinued near

the end of the growing season. The number of generations

depended on the date of first appearance of adults, with 2 to 4

complete generations developing. Additional, partial generations

also occurred. Similar results have been reported in previously

published studies involving soybean (Raney and Yeargan 1977,

Pitre et al. 1978, Correa et al. 1977, Shepard et al. 1974a,

Dietz et al. 1976). Our results indicate that damsel bugs are









common, indigenous predators in soybean during mid or late season

throughout our geographical area, and enhancement and conserva-

tion of their populations should be a priority in soybean IPM

programs.

Nymphal populations were aggregated in nearly all situations

in the soybean fields sampled in our study. Adult populations

were slightly aggregated to random. Our data was taken from a

wide range of densities in a number of fields over two growing

seasons and provides strong evidence that these results are

typical for nymphal and adult populations in soybean. Our

results contrast with the conclusion by Waddill et al. (1974)

that populations of damsel bugs were best described by the

poisson distribution and therefore were random. Sample estimates

of adults and nymphs were combined in their analyses, which

undoubtedly influenced their results. Our results for adults and

nymphs are in close agreement with results reported by Bechinski

and Pedigo (1981).









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