Effect of Four Soybean Cropping Systems on the Abundance of Foliage-Inhabiting Insect Predators

Abstract

Foliage-inhabiting predators were collected in sweep nets in four soybean cropping systems(full season, conventionally plowed; full season, drill planted; no till, double cropped soybeans after barley; and no till, double cropped soybeans after wheat) in Westmoreland County, Virginia, during 1981 and 1982. In both years, Orius insidiosus (Say) was the most abundant insect predator, followed by Nabis roseipennis Reuter. Geocoris spp. were fourth most abundant in 1981 and third in 1982. Coccinellids were third most abundant in 1981 and fourth in 1982. Total predator counts on the foliage were highest in August and early September, at the time of soybean podfill. While O. insidiosus, N. roseipennis , and Geocoris spp. were more abundant in drill-planted fields, coccinellids were most numerous in double-cropped barley-bean and drill-planted fields. Analyses of variance on each sampling date revealed that the total predators were most numerous in barley-bean and drill-planted fields until late August to early September, when predators were more abundant in all three narrow row systems than in conventionally planted fields. At least three factors—planting date, row spacing, and presence of previous crop stubble—may contribute to the enhancement of the natural enemy complex in narrow-row and no-till cropping systems.