Laboratory assays were conducted to determine effect of host plant on mortality of the southern corn rootworm,Diabrotica undecimpunctata howardiBarber, from the entomopathogenic nematodesSteinemema carpocapsaeWeiser andHeterorhabditis bacteriophoraPoinar and on nematode progeny production. Mortality ofD. u. howardi, as well as nematode progeny production, varied according to the host plant on which the rootworms had fed. Mortality fromS. carpocapsaewas lower for rootworms that had fed on peanut roots than for rootworms that had fed on squash or com roots. Mortality fromH. bacteriophorawas lower for rootworms that had been reared on corn roots than for rootworms that had fed on peanut or squash roots. For both nematodes, progeny production from larvae that had fed on squash roots was significantly lower than progeny production from rootworms that had fed on com or peanut roots. Host plant effects involving entomopathogenic nematodes and a soil-inhabiting stage of an insect pest have not been previously demonstrated.