Research Accomplishment Reports 2007

Dynamic Soybean Pest Management for Evolving Agricultural Technologies and Cropping Systems

K.V. Yeargan
Department of Entomology

 

Project Description

The overall project addressed new and evolving pest problems that affect soybeans. Kentucky's participation specifically addressed Sub-Objective 3-B., Conserving Natural Enemies. We found the nocturnal, predatory harvestman Phalangium opilio was among the most frequently observed predators of corn earworm eggs in Kentucky soybean fields (second to Nabis spp. and sometimes third to Geocoris spp.). This opilionid predator also was observed feeding on the soybean aphid, Aphis glycines. We compared the reproductive performance of P. opilio on three diets: corn earworm eggs (monotypic diet), soybean aphids (monotypic diet), and a combination of those two prey (mixed diet). The soybean aphid adversely affected the reproductive biology of this predator through higher mortality, smaller body size, and lower fecundity.

We studied photoperiodic induction of hibernal diapause in the predatory bug, Geocoris uliginosus. Offspring of field-collected bugs were reared in environmental chambers under six photoperiods, ranging from 10:14 (L:D) to 15:9, all at 24 degrees C. The critical photoperiod for diapause induction was identified as being approximately 13:11. We determined that the nymphal stage is sensitive to the critical photoperiod.

The predatory bigeyed bugs Geocoris punctipes and G. uliginosus are sympatric throughout most of the eastern USA. Studies of cannibalism by, and intraguild predation between, G. punctipes and G. uliginosus were conducted to determine potential interactions within and between these predaceous species that might reduce their populations. Adult females did not kill any adult males in cannibalism tests with G. punctipes or G. uliginosus. All other tested combinations of stages/instars resulted in cannibalism, but the rates were generally low, ranging from 4.5 to 18.2%. Our results contradict an earlier report that G. uliginosus is highly cannibalistic. We did not find G. uliginosus to be more cannibalistic or more likely to engage in interspecific predation than G. punctipes.

We studied the effect of presence of conspecific males on reproduction by the predator Nabis americoferus. After mating and first oviposition, half of the female N. americoferus were isolated without males and half were kept with males for the remainder of their life. Females lived 22% longer and laid 21% more eggs in the absence of males than in their presence. Similar studies have been initiated with G. punctipes, but these have not been completed.

Impact

These studies contribute to our understanding of native natural enemies that attack soybean pests, specifically factors that affect the predators' seasonal phenology and abundance. They also show how certain natural enemies respond to the exotic pest species Aphis glycines (soybean aphid).

Publications

Allard, C. M. 2003. Diel activity patterns and distribution of Phalangium opilio in soybean and the effect of diet on female reproduction. M.S. Thesis, University of Kentucky. 68 pp.

Brannon, S.L. 2004. Factors relevant to potential commercial rearing of the hemipteran predator Geocoris uliginosus: cannibalism and photoperiodic induction of reproductive diapause. M.S. Thesis, University of Kentucky. 41 pp.

Allard, C.M., and Yeargan, K.V. 2005. Effect of diet on development and reproduction of the harvestman Phalangium opilio (Opiliones: Phalangiidae). Environmental Entomology 34:6-13.

Allard, C. M., and Yeargan, K.V. 2005. Diel activity patterns and microspatial distribution of the harvestman Phalangium opilio (Opiliones, Phalangiidae) in soybeans. Journal of Arachnology 33:745-752.

Brannon, S.L., Decker, K.B., and Yeargan, K.V. 2006. Photoperiodic induction of reproductive diapause in the predator Geocoris uliginosus (Hemiptera: Geocoridae). Annals of the Entomological Society of America 99: 300-304.