Beneficial role of corn leaf aphid, Rhopalosiphum maidis (Fitch) (Homoptera: Aphididae), in maintaining Hippodamia spp. (Coleoptera: Coccinellidae) in grain sorghum

Abstract

The significance of corn leaf aphid, Rhopalosiphum maidis (Fitch), as a food source for the natural enemies of greenbug, Schizaphis graminum (Rondani), was determined in the Texas High Plains sorghum agroecosystem. The most abundant coccinellid species were Hippodamia convergens (Guerin-Meneville) and H. sinuata (Mulsant). Neither coccinellid species showed any preference for either greenbug or corn leaf aphid in replicated choice predation tests. Corn leaf aphid and coccinellid densities increased at similar rates in the early season during both 1982 and 1983. Regression analyses suggested that variation in corn leaf aphid and greenbug densities significantly contribute to the variation in coccinellid densities. Furthermore, corn leaf aphid and coccinellid densities were significantly and positively correlated prior to sorghum panicle emergence. However, after panicle emergence only greenbug and coccinellid densities were highly correlated, reflecting a change in coccinellid food source from primarily corn leaf aphids to greenbugs. The ability of coccinellids to regulate greenbug densities may be largely dependent on the abundance of corn leaf aphids as a food source during early season crop growth.