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
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.
HENRY CO., AL
DALLAS CO., AL
w 30- ***"......ELMORE CO., AL
-------GADSDEN CO., FL
z 10- i1
.... ....... '' .. ---....--
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.
----- GADSDEN CO.,FL
r 40- DALLAS CO., AL
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
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
1985 DALLAS CO., AL
1986 DALLAS CO., AL
1986 GADSDEN CO., FL
1985 ELMORE CO., AL
*Significantly > 1 (P < 0.05) by a X2 test
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).
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
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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