Coccinellids in Cotton: Population Response to Pesticide Application and Feeding Response to Cotton Aphids (Homoptera: Aphididae)

Abstract

Four treatments were evaluated during 1997 and 1998 to determine the effects of pesticides on coccinellid densities: (1) untreated control, (2) foliar applications of a systemic insecticide, imidacloprid (Provado 1.6 F), when spray thresholds of aphid numbers were exceeded in all plots, (3) weekly foliar applications of a fungicide, chlorothalonil (Bravo 720), and (4) weekly foliar applications of imidacloprid (Provado 1.6 F). The coccinellids observed in Georgia cotton during the study included Hippodamia convergens Guerin-Meneville, Scymnus spp., Harmonia axyri- dis (Pallas), Coccinella septempunctata L., and Coleomegilla maculata (Mulsant). During 1997, H. convergens and Scymnus spp. comprised 75 and 15%, respectively, of all coccinellids observed during the study. During 1998, Scymnus spp. comprised 44% of all coccinellids, and H. convergens comprised 33%. Coccinellid population densities closely tracked those of cotton aphids during both years. Cotton aphid and coccinellid densities were greatest in the chlorothalonil treatment during both years of the study. In functional feeding response experiments, fourth-instar and adult Scynmus creperus exhibited a type II functional response to A. gossypii density under laboratory conditions. Fourth instars exhibited a higher search rate and shorter handling time than adult S. creperus. Collectively, coccinellids are a valuable component of the cotton aphid's natural enemy complex.