Synergism of imidacloprid and an entomopathogenic nematode:: A novel approach to white grub (Coleoptera: Scarabaeidae) control in turfgrass

Combinations of the insecticide imidacloprid and entomopathogenic nematodes were tested for control of white grubs. In greenhouse tests, field-collected 3rd-instar white grubs were placed in pots with grass treated with imidacloprid, the entomopathogenic nematode Heterorhabditis bacteriophora (Poinar), or both. Combinations of imidacloprid and nematodes had a strong synergistic effect on mortality at imidacloprid concentrations ranging between 50 to 200 g (AI)/ha. This effect was observed when imidacloprid and the nematodes were applied at the same time or when imidacloprid was applied first followed by the nematodes 14 d Inter. The synergistic interaction occurred against a nematode-susceptible scarab species, Cyclocephala hirta LeConte, and against a more nematode-resistant scarab species, C. pasadenae Casey. When infective juveniles of Ii. bacteriophora were agitated in solutions of imidacloprid for 24 h, no negative effect on their survival and infectivity was observed.