-/3
Soil Fertility Effects on Population Dynamics
of Soybean Insect Predators
I. D. Teare*, F. M. Rhoads, and J. E. Funderburk
SSEP 18 1990
University of Florida
I. D. Teare, Agronomy Dep.; F. M. Rhoads, Dep. of Soils; J. E.
Funderburk, Entomology and Nematology Dep.; North Fla. Res. and
Educ. Ctr. Contribution from the Institute of Food and
Agricultural Sciences, Univ. of Fla. Route 3 Box 4370, Quincy, FL
32351. Research Report NF 90-13.
INTRODUCTION
The vegetation throughout the agrosystem can be selectively
modified by soil fertility to adversely affect pest populations
(Rhoads et al., 1990) and we have found no studies where
beneficial insects [Geocoris spp. (bigeyed bugs), Nabis and
Reduviolus spp. (damsel bugs) and Araneae (spiders)] population
dynamics in soybean were studied in relation to soil fertility.
Large populations of bigeyed bug [Geocoris punctipes (Say)]
occur in soybean fields in the southern U.S. (Shepard et al.,
1974). Bigeyed bugs are predators of Anticarsia gemmatalis
Hubner (Elvin et al.,1983), Nezara viridula (L.) (Crocker and
Whitcomb, 1980), Heliothis zea..Boddie .(Whitconqb and Bell, 1964),
H. virescens, (F.) N(McDaniel and Sterling, 1979), and
Pseudoplusia includes (alker) (Richman et al., 1980).
Reduviolus rosepiennis Reu'ter "i~'"the most common species of
damsel bug comprising over 90% of all individuals occurring in
soybean fields in the Southeast (Dietz et al. 1976). Other
damsel bugs found in soybean are R. alternatus Parshley, R.
americoferus Carayon, Nabidae capsiformis Germar, and N.
deceptivus Harris. 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).
Spiders are one of the more abundant groups of arthropods in
the agroecosystem and often outnumber other predaceous insects in
crops (Whitcomb, 1980). Among the many species identified in
2
soybean, Oxyopes salticus Hentz and Chiracanthium inclusum Hentz
are thought to rank first and second, respectively, in seasonal
abundance (Dietz et al., 1976). Oxyopidae (green lynx spiders)
are most common in North Florida. These spiders are found
predominately in the upper zone B as described by Whitcomb
(1980). All spiders are obligate carnivores. The mere fact that
spiders are predators does not mean that they are are entirely
beneficial. Whitcomb (1980) list them as being: 1. primary
consumers of immature and adults of many pest species, 2. natural
enemies of predatory insects (lady beetles, lacewings, etc.), 3.
a food source for other predators and beneficial, 4. competitors
with other predators and beneficial when prey become limiting.
As a result, the same spider species may be beneficial in one
field and pestiferous in another.
Most reports in the literature indicate that populations of
bigeyed bug, damsel bug, and spiders in soybean increase along
with pests and reach greatest densities during mid- or
late-season (Raney and Yeargan, 1977; Deitz et al., 1976; Shepard
et al., 1974; and Pitre et al., 1978; Funderburk and Mack, 1987;
Correa et al., 1977; Mack and Funderburk, 1987; Funderburk et
al.,1988).
Enhancement and conservation of beneficial predators is a
major priority in soybean integrated pest management programs.
Insecticides used to control crop pests may also kill beneficial
predators, and the pest frequently reinvades the field at a
faster rate than beneficial. Pest numbers then build up rapidly
because there are few beneficial predators. Integrated pest
3
management strategies in soybean are designed to use insecticides
only when pest populations reach economically damaging numbers
and even then to selectively use insecticides in ways that reduce
pest populations, but have the least negative impact on predator
populations.
Soil fertilizer operations modify foliage habitats where many
pest and natural enemies reside during at least part of their
life cycle (Rhoads et al., 1990). These modifications can alter
survival or development (Herzog and Funderburk, 1986).
Musick (1985) and Herzog and Funderburk (1986) concluded that
each crop and insect situation must be evaluated individually and
control decisions made for each specific geographical location.
The primary purpose of this study was to determine the effect of
soil fertility on population dynamics and population sizes of
bigeyed bugs, damsel bugs, and spiders in a subsequent soybean
crop following a winter wheat crop. This information should aid
in implementation of cultural control strategies in integrated
pest management programs in relation to soil fertility in a
production systems that conserve natural enemies in soybean field
in the southeastern U.S.
MATERIALS AND METHODS
Soybean were grown on a Norfolk loamy sand (fine, loamy,
siliceous, thermic Typic Kandiudult) at Quincy, FL. Soil samples
were collected from each plot in Feb of each year. This
experiment was conducted in 1986 and 1987 at the North Fla. Res.
and Educ. Ctr. on land which was previously used for fertility
research. Previous soil treatments [P at 0, 27, 54, 107 lb A-
4
applied annually as triple superphosphate for 6 yr; K at 0, 188,
and 375 lb A' applied annually as KCL for 6 yr; N at 0, 60, and
120 lb A-1 each year as ammonium nitrate] are described in Rhoads
and Barnett (1985). Ten cores 1 X 6 inches were taken from each
plot in a criss-cross pattern, composite, air-dried, and ground
to pass a 0.08 inch sieve for analysis. Melich I soil extractant
was used. Soil-test levels (ppm) in relation to treatment code
are shown in Table 1.
Soybean followed wheat in 1986. No P was applied to wheat or
soybean in 1986 because residual levels of P were adequate as
indicated by soil test (Table 1).
Potassium was applied in 1986 as follows:
to wheat K1 = 0, K2 = 84 lb K A- K3 = 168 lb K A-1
-1 -1
to soybean K1 = 0, K2 = 42 lb K A K3 = 84 lb K A
Magnesium was applied in 1986 to wheat only as follows:
1 -1
Mg1 = 0, Mg1 = 60 lb Mg A Mg3 = 120 lb Mg A
Soybean followed snap bean and cabbage in 1987. No P or Mg
was applied to snap bean, cabbage or soybean in 1987.
Potassium was applied in 1987 to soybean only as follows:
to soybean K, = 0, K2 = 42 lb K A1, K = 84 lb K A1.
A 2-row cone planter was used to plant Braxton soybean at a"
planting rate of 40 lb A-1 at 1 inch soil depth on 11 June 1986
and 10 June 1987.
In 1986 and 1987, 1 inch water A-1 was applied preplant and
at intervals during the growing season when tensiometers placed
at 6 inches soil depth reached 0.02 MPa. Insecticides were not
applied at any time during the experiment.
5
Nymphal and adult population densities were estimated on 8
calendar dates/Julian date in 1986 (7-1/182, 7-12/193, 7-23/204,
8-5/217, 8-14/226, 8-26/238, 9-9/252, 9-22/265) and on 7 calendar
dates/Julian date in 1987 (7-8/189, 7-22/203, 8-7/219, 8-18/230,
9-2/245, 9-14/257, 9-29/272). Sampling was begun at early
vegetative stage (V4) and continued until late seed stage (R6) in
both years.
Insect sampling was carried out as described by Irwin and
Shepard (1980) and Whitcomb (1980). All plots were sampled on
each sampling date by beating the plants on both sides of the row
into a 0.9-m square ground cloth placed between the rows. Three
samples were taken per plot on each sampling date. Also,
adjacent plants were searched at their base and the soil surface
was visually examined for bigeyed bug, damsel bug and spiders.
The influence of nutrient level on population densities and
population cycles of bigeyed bug and damsel bug nymphs, and
spiders were evaluated by ANOVA. Data from each growing season
were analyzed separately. The design was a split plot over time.
The main effect compared the influence of soil nutritional level
on seasonal population density. Orthogonal comparisons were used
to define nutrient level differences. The interaction of date X'
treatment compared the influence of soil nutrient level on
seasonal population cycles.
RESULTS AND DISCUSSION
A description of soybean yield in relation to soil fertility
levels of P, K, and Mg in 1986 and 1987 is given in Table 2.
Mean yields were significantly greater for the P P3, and P4
6
levels than the Pi level for both years (1986: F=7.43; df=1,21;
P<0.05 and 1987: F=13.81; df=1,30; P<0.01) but significantly
similar for the P,, P and P4 levels in 1986, but in 1987 P3 and
P4 fertility levels were significantly greater than at the P2
level (F=5.85; df=1,30; P<0.05). Yields were significantly
greater both years for the K, and K, levels than the K level
(1986: F=2.88; df=1,21; P<0.10 and 1987: F=7.34; df=1,30;
P<0.01), with yields similar for the K2 and K, levels. Yields
were not significantly affected by Mg fertility levels in 1986
and 1987.
Insect data for individual treatments are reported in terms
of population densities and cycles which, when combined over
date, describe seasonal population dynamics (Fig. 1, 2, 3, 4).
Population densities are described in terms of daily and seasonal
variation. Population cycles are recognized in figures in
relation to insect numbers and stage, and date or plant
physiological stage.
Population densities of damsel bug nymphs (DBN) were very low
each year until soybean Growth Stage R4; then, densities
increased in all treatments until R6 in 1986 and R5 in 1987.
Population densities of DBN differed between fertility treatments"
in 1986 (F=2.4; df=7,21; P<0.06) but in 1987 was nonsignificant.
Orthogonal comparisons were used to separate the effects of P, K,
Mg levels on DBN population densities. Estimates were similar
for P4 and P, in 1986,but P3 was greater than P2 and P, levels
(F=13.0; df=1,21; P<0.01) (Fig. 1). Population cycle increases
were earlier in 1986 according to fertilizer treatment,
P4>P,>P2>P
Orthogonal comparisons revealed that density estimates of DBN
were not significantly affected by K or Mg in 1986 or 1987.
The population densities of bigeyed bug nymphs (BBN) differed
between fertility treatments in 1986 (F=2.3; df=7,21; P<0.07) and
1987 (F=3.3; df=10,30; P<0.01). Orthogonal comparisons were used
to separate the effects of P, K, and Mg levels on BBN population
densities. Density estimates were significantly affected by P
levels. Population cycles of BBN for treatments at different
levels of P, but constant levels of K and Mg, are shown in Figure
2 to illustrate the effect of P on density estimates. Mean
densities were significantly greater in treatments at the P4
level compared with densities in treatments at the P P and P3
levels in 1986 (F=6.0; df=l,21; P<0.05)and in 1987 (F=6.5;
df=10,30; P<0.05). Mean densities also were significantly
greater in treatments at the P3 level than in treatments at the
P1 and P2 levels in 1986 (F=7.8; df=1,21; P<0.05), but not
significant in 1987.
Density estimates of BBN were significantly affected by Mg in
1987 (Fig. 3), but not in 1986. Population cycles of BBN for'
treatments at different levels of Mg, but constant levels of P
and K are shown in Figure 3. Orthogonal treatment comparisons
were used to show that estimates in 1987 were significantly
greater in treatments at the Mg2 and Mg, levels than at the Mg,
level (F=6.4; df=1,30; P<0.05), with estimates significantly
different between the Mg2 and Mg3 levels (F=12.8; df=1,30;
8
P<0.01). Orthogonal comparisons also revealed that BBN estimates
were not significantly affected by K levels in 1986 or 1987 (data
not shown).
The treatment x date interaction was used to determine if
fertilizer treatment influenced population cycles. This
interaction was significant for VBC in 1986 (F=1.53; df=49,168;
P<0.05) and not in 1987.
The density estimates of spiders differed between .fertility
treatments in 1986 (F=3.3; df=7,21; P<0.05), but not in 1987.
Population cycles of spiders at different levels of P, but
constant levels of K and kg, are shown in Figure 4. Orthogonal
treatment comparisons revealed that density estimates were
affected by P levels. Mean densities were significantly greater
at the P4 level than at the P,, P2, and P3 levels (F=3.1;
df=1,21; P<0.10) and at the P3 level than at the P2 and P1 levels
(F=14.9; df=1,21; P<0.01).
Orthogonal comparisons revealed that density estimates of
spiders were not significantly affected by K or Mg in 1986 and
1987 (data not shown).
Fertility levels of P, therefore, affected population
dynamics of DBN, BBN, and spiders. In 1986, increased fertility-
levels of P that did not result in a significant yield increase
did result in significant increases in beneficial insect
population densities, but in 1987 significant increases were only
observed in BBN population densities. Although yields were
statistically similar at the P2 P3, and P4 levels, population
densities of DBN were significantly increased from P2 to P3 (P3
9
similar to P ) in 1986 and population densities of BBN were
significantly increased from P3 to P4 in both years and P2 to P3
in 1986.
Population densities of DBN, BBN, and spiders in 1986 and
1987 were not significantly affected by K levels, even at levels
significantly affecting soybean yield.
Although Mg levels sometimes affected soybean yield, pest
population densities were only significantly influenced by Mg
levels on population densities of BBN in 1987.
The reason why soil fertility levels affected population
dynamics of these major\ beneficial is unexplained. Soil
fertility level may be directly affecting pest populations
through alterations in crop growth or nutritional level (Rhoads
et al., 1990) and indirectly affecting important natural enemies
of the pests, such as bigeyed bugs, damsel bugs, and spiders.
Our results showing effects of soil fertility on population
dynamics of the major beneficial of soybean in the extreme
southern U.S. are useful for integrated pest management programs
in the region. Current recommendations for soil fertility levels
necessary to obtain optimal soybean yields should be followed
closely. In addition to reducing the cost of fertilizer, it will
also reduce the likelihood of pest outbreak and the need for
additional costs associated with pest control.
REFERENCES
Adkisson, P.L. 1958. The influence of fertilizer applications
on population of Heliothis zea (Boddie), and certain insect
predators. J. Econ. Entomol. 51:757-759.
Buschman, L.L., W.H. Whitcomb, R.C. Hemenway, D.L. Mays, Nguyen
Ru, N.C. Leppla, and B.J. Smittle. 1977. Predators of
velvetbean caterpillar eggs in Florida soybean. Environ.
Entomol. 6:403-407.
Correa, B.S., A.R. Pannizzi, G.G. Newman, and S.G. Turnipseed.
1977. Distribuicao geografica e adundancia estacional dos
principals insectos-pragas da soja e seus predadores. An.
Soc. Entomol. Brasil 6:40-50.
Crocker, R.L., and W. H. Whitcomb. 1980. Feeding niches of the
big-eyed bugs Geocoris bullatus, G. punctipes, and G.
uliginosus (Hemiptera:Lygaeidae:Geocorinae). Environ.
Entomol. 9:508-513.
Deitz, L.L., J.W. Van Duyn, J.R. Bradley, Jr., R.L. Rabb, W.M.
Brooks, and R.E. Stinner. 1976. A guide to the
identification and biology of soybean arthropods in North
Carolina. N.C. Agric. Exp. Sta. Bull. 238. 264 pp.
Elvin, M.K., J.L. Stimac,\and W.H. Whitcomb. 1983. Estimating
rates of arthropod predation on velvetbean caterpillar larvae
in soybeans. Fla. Entomol. 66:230-330.
Funderburk, J.E., and T.P. Mack. 1987. Abundance and dispersion
of Geocoris spp. (Hemiptera:Lygaeidae) in Alabama and Florida
soybean fields. Fla. Entomol. 70:432-439.
Funderburk, J.E, and T.P. Mack. 1989. Seasonal abundance and
dispersion patterns of damsel bugs (Hemiptera:Nabidae) in
Alabama and Florida soybean fields. J. Entomol. Sci. 24:9-15.
Funderburk, J.E., D.L. Wright, and I.D. Teare. 1988. Preplant
tillage effects on Population dynamics of soybean insect
predators. Crop Sci. 28:973-977.
Herzog, D.C., and J.E. Funderburk. 1986. Ecological bases for
habitat management and cultural control. In: M. Kogan (ed.)
Ecological theory and integrated pest management practice.
Wiley Interscience, N.Y. p. 217-250.
Irwin, M.E., and M. Shepard. 1980. Sampling predaceous
hemiptera on soybean, pp. 505-531. In: M. Kogan and D.C.
Herzog (ed.) Sampling Methods in Soybean Entomology.
Springer-Verlag, Inc. New York.
McDaniel, S.G., and W.L. Sterling. 1979. Predator determination
and efficiency on Heliothis virescens eggs in cotton using
32-P. Environ. Entomol. 8:1083-1087.
McCarty, M.T., M. Shepard, and S.G. Turnipseed. 1980.
Identification of predaceous arthropods in soybeans using
autoradiography. Environ. Entomol. 9:199-203.
Musick, G.J. 1985. Management of arthropod pests in con-
servation-tillage systems in the southeastern U.S. p.
191-204. In: W.L. Hargrove, F.C. Boswell, and G.W. Langdale
(ed.) Proceedings of the 1985 southern region no-till
conference. July 16-17, 1985. Griffin, Ga.
Pitre, H.N., T.L. Hillhouse, M.C. Donahoe, and H.C. Kinard.
1978. Beneficial arthropods on soybean and cotton in
different ecosystems in Mississippi. Miss. Agric. For. Exp.
Sta. Tech. Bull. 90. 9pp.
Raney, H.G., abd K.V. Yeargan. 1977. Seasonal abundance of
common phytophagous and predaceous insects in Kentucky
soybeans. Trans. Ky. Acad. Sci.38:83-87.
Rhoads, F.M. 1990. Soil fertility effects on soybean yield in
the Southeast. Univ. of Fla. Res. and Educ. Ctr.. Quincy,
FL, Res. Rep. NF-90-14. p. 1-10.
Rhoads, F.M., and R.D. Barnett. 1985. Nutritional requirement of
high yield cropping systems in the Southeast. Annual Report,
IFAS, Quincy, FL. Potash and Phosphate Institute, Atlanta,
Ga.
Richman, D.B., R.C. Hemenway, and W.H. Whitcomb. 1980. Field
cage evaluation of predators of the soybean looper,
Psuedoplusia includes (Ledidoptera:Noctuidae). Environ.
Entomol. 9:315-317.
Shepard, M., G.R. Carner, and S.G. Turnipseed. 1974. Seasonal
abundance of predaceous arthropods in soybeans. Environ.
Entomol. 3:985-988.
Sloderbeck, P.E., and K.V. Yeargan. 1983. Comparison of Nabis
americoferus and Nabis roseipennis (Hemiptera: Nabidae) as
predatorof the green cloverworm (Lepidoptera:Noctuidae).
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and mites of Arkansas cotton fields. Ark. Agric. Exp. Stn.
Bull. 690:1-84.
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ACKNOWLEDGEMENTS
Our thanks to E. Brown, Senior Laboratory Technician; A.
Brown, Agricultural Supervisor; A. Manning, Biological
Scientist II; North Fla. Res. and Educ. Ctr., Univ. of Fla.
Quincy FL 32351; for data anaylsis and illustration, data
collection, and plot preparation and management.
Table 1. Soil tests for use in soybean-fertility-pest experiment
in 1986 and 1987 at Quincy FL.
Soil-test levels (ppm) across reps.
P, = 10
K = 31
Mg, = 40
PI = 7
1
K, = 32
Mg, = 33
P = 21
K2 = 55
Mg2 = 89
P2 = 15
K2 = 65
Mg2 = 50
P3 = 35
3
K3 = 73
Mg3 = 71
P = 33
3
K3 = 81
Mg3 = 47
P4 = 82
P = 75
4
Table 2.
Year
Soybean yields (bu/A) in relation to fertility treatment
and year with no pesticide treatment, Quincy FL.
Soybean yield (bu/A) for fertility treatments across reps.
P, = 10
K = 17
Mg1 = 20
P, = 10
K, = 13
Mgi = 16
P2 = 22
K2 = 20
Mg2 = 25
P2 = 14
K2 = 17
Mg2 = 20
P3 = 25
K = 25
Mg, = 28
P = 20
K, = 20
Mg9 = 18
Year
1986
1987
1986
1987
P4 = 25
P4 = 17
R1R2 R4 R5 R6 R6
0
oe
u- M R 1 W i I I i I I 0 --
180 189 203 217 226 238 252 285 275 285 180
Day of Year
Figure 1.
Mean population density of damsel bug nymphs in relation to
day of year (Days Julian, 1986 and 1987) and physiological
stage of soybean development in treatments differing in soil
fertility levels of P, but at the same level of K and Mg.
189 203 217 228 238 252 285 275 285
V3 V5.5 R1 R2
R4 R5 R6 R6
V3 V5.5
R4 R5 R6 R6
R3 R4 R5
0
0:
I -
180 189 203 217 226 238 252 265 275 285
180 189
180 189
Day of Year
Figure 2.
Mean population density of bigeyed bug nymphs in relation to
day of year (Days Julian, 1986.and 1987) and physiological stage
of soybean development in treatments differing in soil
fertility levels of P, but at the same level of K and Mg.
203 217 226 238 252 265 275 285
V3 V5.5 R1 R2
V4 R1.5
R6 R6
R3 R4 R5 R6 R6
203 217 226 238
265 275 285
1987
p 1 3 3K
30 189 203 217 226 238 252 265 275 285
Day of Year
Mean population density of bigeyed bug nymphs in relation to
day of year (Days Julian, 1986 and 1987) and physiological
stage of soybean development in treatments differing in soil
fertility.levels of Mg, but at the same level of P and K.
0
1or
T-
'E
>O
(D
0)
M
5
1986
4
3
2 3
2 MgIPI K3
Mg 2-K--
0 f ^ -- -- i -- | -- | -- --I -1 l --
180 189
Figure 3.
R4 R5 R6 R6
V4 R1-2
V3 V5.5 R1 R2
R3 R4 R5 R6 R6
180 189 203 217 228 238 252 265 275
-- o--- '-
285 180 189
203 217 226 238 252 265 275 285
Day of Year
Mean population density of spiders in relation to day of year
(Days Julian, 1986 and 1987) and physiological stage of
soybean development in treatments differing in soil fertility
levels of P, but at the same level of K and Mg.
Figure 4.
V3 V5.5 R1 R2
R4 R5 R6 R6
V4 R1.5
|