Biotic Control of Cotton Aphids (Homoptera: Aphididae) in Cotton Influenced by Two Insecticides

Abstract

During 1989 and 1990, we conducted field studies to determine effects of the pyrethroid cypermethrin and the organophosphate sulprofos on natural enemy densities and on the efficacy of natural enemies against the cotton aphid, Aphis gossypii Glover. During 1989 in untreated plots, small predators had the greatest impact on the aphid population, aphidopathogenic fungi had the greatest impact in the sulprofos-treated cotton, and no single biotic mortality factor was predominant in the cypermethrin-treated cotton. In 1990, small predators were the primary mortality factor in all treatments, but they were most effective in the untreated cotton. Predator-induced mortality was lower in insecticide-treated plots than in untreated plots. The aphid parasitoid, Lysiphlebus testaceipes (Cresson), was never abundant in any treatment, but significantly more were found in the sulprofos-treated plots, which contained the most aphids, than in the other treatments. On the basis of population densities, key predators were Geocoris spp. and araneids during 1989 and Geocoris spp. during 1990. Simple linear correlation analyses suggested density-dependent relationships between aphid populations and aphidopathogenic fungi, parasitoids, combined predator populations, and coccinellids. However, these relationships were inconsistent between years and treatments. Aphidopathogenic fungi were the only mortality factor that demonstrated a well-defined cause-effect relationship with cotton aphid population densities.