1 /VA- Soybean Tillage vs. Predators and Pests 8/
02 '7-/O I.D. Teare*, D.L. Wright, and J.E. Funderbdi/ ,
3 ABSTRACT ^ %
4 Soil tillage can influence the population -.y s of
5 arthropod pests and their natural enemies. Our objective was t
6 relate population densities of each predator [Geocoris spp.
7 (bigeyed bug) and Nabis and Reduviolus spp. (damsel bug)] to pest
8 densities [Anticarsia gemmatalis (Hubner), Plathypena scabra (F.),
9 and Nezara viridula (L.)]. Densities of all predators were
10 positively related to pest densities of A. cemmatalis and N.
11 viridula in 1985 and 1986. These positive correlations indicate
12 that observed differences between tillage treatments in bigeyed bug
13 and damsel bug predator populations were in response to the
14 abundance of A. gemmatalis and N. viridula. Populations of bigeyed
* bugs and damsel bugs were not correlated with P. scabra in either
25 North Fla. Res. and Educ. Ctr., Quincy FL 32351, Institute of
26 Food and Agricultural Sciences, Univ. of Fla., Gainesville, FL
S 32611. Research Report NF-92-10.
2 Enhancement and conservation of beneficial predators is a
3 major priority in soybean integrated pest management (IPM)
4 programs. IPM strategies in soybean are designed to use
5 insecticides only when pest populations reach economically damaging
6 numbers and even to selectively use insecticides in ways to reduce
7 pest populations, but not result in a negative effect on predator
9 The statistical technique where insect predator and pest
10 densities are averaged over dates of sampling and tested by simple
11 linear regression has been used to determine if increases in
12 beneficial insect densities were the indirect effect of the
13 treatments (i.e., tillage, fertilizer) on increased pest densities
14 or the direct effect of the beneficial insect population
15 supplementing it's diet from the soybean treated plants [realizing
16 that most beneficial do minor feeding on plants (Naranjo and
17 Stimac, 1985) which suffer no damage from this feeding (Ridgeway
18 and Jones, 1968)].
19 The objective of this study was to study the relationships
20 each year (1985 and 1986) between pest and predators by simple
21 correlations of numbers of bigeyed bugs and damsel bugs in each
22 plot on each sample date with respective numbers of A. gemmatalis,
23 P. scabra and N. viridula.
1 MATERIALS AND METHODS
Soybean was grown on a Norfolk sandy loam soil (fine-loamy,
3 siliceous, thermic Typic Paleudult) at Quincy, Florida. Cobb was
4 planted on 30 July 1985 and Kirby was planted on 11 June 1986.
5 Nymphal and adult population densities of beneficial and pests
6 were sampled on 23 Aug, 4 and 28 Sept, 9 Oct, and 11 Nov in 1985
7 and 3, 15, 24 July, and 12 and 28 Aug in 1986 by beating the plants
8 on both sides of the row into a 0.9 m ground cloth placed between
9 the rows. Cultural methods and field plot design are described in
10 detail in Funderburk et al. (1988 and 1990) and will not be
11 repeated here.
12 Densities of bigeyed bugs and damsel bugs were estimated in
13 the Funderburk et al. (1988) study, and densities of A. gemmatalis,
14 P. scabra, and N. viridula were estimated in Funderburk et al.
is (1990) study. Relationships each year between the pests and the
16 predators were evaluated by simple correlations of the number of
17 bigeyed bugs and damsel bugs in each plot on each sample date with
18 respective number of A. qemmatalis, P. scabra, and N. viridula.
1 RESULTS AND DISCUSSION
2 Economically important pest and beneficial insects in the
3 study were A. gemmatalis, P. scabra, and N. viridula; and bogeyed
4 bug and damsel bug, respectively. Population densities of these
5 insects are contained in Funderburk et al. (1990 and 1988,
7 Population densities of bigeyed bugs and damsel bugs were
8 significantly (P<0.05) correlated (based on r-values) with A.
9 gemmatalis in 1985 and 1986. Population densities of bigeyed bugs
10 were also significantly correlated with N. viridula in 1985 and
11 1986. Population densities of damsel bugs were significantly
12 correlated with N. viridula in 1985, but not in 1986. Population
13 densities of bigeyed bugs and damsel bugs were not correlated with
14 P. scabra either year. The r-value was positive for each
15 significant relationship in 1985 and 1986; consequently, predator
16 populations of bigeyed bugs and damsel bugs increased directly as
17 populations of A. gemmatalis and N. viridula increased.
18 These positive correlations indicate that observed differences
19 between tillage treatments in bigeyed bug and damsel bug predator
20 populations were in response to abundance of A. gemmatalis and N.
21 viridula, which undoubtedly were serving as their primary food
* Our thanks to E. Brown, Senior Laboratory Technician; A. Brown,
3 Agricultural Supervisor; B. Kidd, Biological Scientist II; North
4 Fla. Res. and Educ. Ctr., Univ. of Fla, Quincy, FL 32351; for data
5 analysis, data collection, and plot preparation and management.
8 Funderburk, J.E., Wright, D.L. & Teare, I.D. (1988) Preplant
9 tillage effects on population dynamics of soybean insect
10 predators. Crop Sci. 28,973-977.
11 Funderburk, J.E., Wright, D.L. & Teare, I.D. (1990) Preplant
12 tillage effects on populations dynamics of soybean insect
13 pests. Crop Sci. 30,686-690.
14 Naranjo, S.E. & Stimac, J.L. (1985) Development, survival, and
reproduction of Geocoris punctipes (Hemiptera:Lygaeidae):
16 Effects of plant feeding on soybean and associated weeds.
17 Environ. Entomol. 14,523-530.
18 Ridgeway, R.L. & Jones, S.L. (1968) Plant feeding by Geocoris
19 pallens and Nabis americoferus. iAnn. Entomol. Soc. Amer.
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