HOST-PLANT EFFECTS ON ENTOMOPATHOGENIC NEMATODES

We conducted assays to determine the effects of host plant and a plant secondary metabolite, cucurbitacin D, on the mortality of Diabrotica undecimpunctata howardi from infection by entomopathogenic nematodes and on nematode progeny production. Rootworms were produced on corn, peanut, and two squash varieties, one containing cucurbitacin D and the other lacking this secondary metabolite. Rootworms were exposed to the NC, HP88, and Lewiston strains of Heterorhabditis bacteriophora and the All, Mexican, and Agriotos strains of Steinernema carpocapsae. The plant on which the rootworms had fed significantly affected rootworm mortality and nematode progeny production. In general, rootworms which had fed on corn suffered significantly lower mortality than those reared on peanuts or either of the squash varieties. Rootworms that had fed on the squash varieties suffered greatest mortality. Nematode progeny production was highest from rootworms that had fed on corn, lower for peanut, and lowest on squash. Progeny production from rootworms that had fed on bitter squash was lower than from nonbitter squash for all nematode strains tested, Possible;effects of cucurbitacins and plant primary metabolites on rootworms and entomopathogenic nematodes are discussed. (C) 1995 Academic Press, Inc.