INTERACTION OF INSECTICIDES, ENTOMOPATHOGENIC NEMATODES, AND LARVAE OF THE WESTERN CORN-ROOTWORM (COLEOPTERA, CHRYSOMELIDAE)

Chemical insecticides and entomopathogenic nematodes have been indepen dently used to suppress corn rootworm damage in maize. We report on th e mortality response of larvae of the western corn rootworm, Diabrotic a virgifera virgifera LeConte, to the combined treatment with 1 of 3 i nsecticides (terbufos, fonofos, and tefluthrin) and the entomopathogen ic nematode Steinernema carpocapsae Weiser (Mexican strain). Corn root worm mortality with combinations of the insecticides terbufos or fonof os and S. carpocapsae was typically additive for the 2 agents. Evidenc e of antagonism between these agents was sometimes observed. The combi nation of tefluthrin with S. carpocapsae frequently resulted in a syne rgistic response and a 24% average increase in expected mortality. The influence of the tefluthrin appears to be isolated to an effect on th e rootworm larvae. Synergism also was observed when tefluthrin was com bined with the nematode Heterorhabditis bacteriophora Poinar (Lewiston strain). The combined use of tefluthrin with an entomopathogenic nema tode may offer an integrated approach to increase the efficacy of ento mopathogenic nematodes for insect control.