Incidence of Arthropod Predators in Different Soybean Cropping Systems

Abstract

The seasonal incidence of nabids, Nabis spp., big-eyed bugs, Geocoris spp., minute pirate bugs, Orius spp., and spiders was examined in conventional, drill-, and double-crop-planted soybean in two localities in eastern Virginia during 1979 and 1980. Population densities of these predators were not sufficiently abundant during the sampling period in 1979 to make statistical comparisons. During 1980, Nabis spp., primarily N. roseipennis Reuter, were significantly more numerous in conventional and drill-planted fields. Geocoris spp., primarily G. punctipes (Say), were significantly higher in conventionally planted fields in Westmoreland County and in drill-planted fields in Richmond County. At both locations, Geocoris were most abundant in the earliest planted fields and were not commonly encountered in double-cropped fields. There were significantly more spiders in the drill-planted fields in Richmond County, and a similar trend was apparent at the other sampling location. Other Arthropod predators commonly encountered in soybean fields included: Podisus maculiventris (Say), Stiretrus anchorago (F.), Hippodamia tredecimpunctata tibialis (Say), Hippodamia convergens Guer., Zelus spp., Sinea spp., Arilus spp., Chrysopa spp., and mantids. No comparisons between population densities in different soybean cropping systems were determined for these species. Population densities of predators in untreated soybean fields were significantly higher during the first six weekly sampling periods than densities in fields treated with disulfoton (1.2 kg of Al/ha) in the furrow at planting.