Synergism of entomopathogenic nematodes and imidacloprid against white grubs: Greenhouse and field evaluation

In previous greenhouse studies, the insecticide imidacloprid and the entomo pathogenic nematode Heterorhabditis bacteriophora Poinar interacted synergi stically against third instars of the masked chafers Cyclocephala hirta LeC onte and C, pasadenae Casey (Coleoptera: Scarabaeidae), We tested this inte raction for two additional nematode species and three additional scarab spe cies under held conditions. In greenhouse tests, H. bacteriophora and Stein ernema glaseri (Steiner) interacted synergistically against third instars o f the Japanese beetle, Popillia japonica Newman, the oriental beetle, Exoma la orientalis Waterhouse, and the masked chafers Cyclocephala borealis Arro w, C. pasadenae, and C. hirta The degree of interaction varied with nematod e species. The strongest synergism occurred between imidacloprid and S. gla seri. Synergism between imidacloprid and H. bacteriophora was weaker and th e interaction was not always significant. Combinations of imidacloprid and S, kushidai Mamiya only resulted in additive mortality, The synergistic int eraction was also observed in field trials but the results were more variab le than those under greenhouse conditions. The combination of nematodes and imidacloprid could be used for curative treatments of white grub infestati ons, especially against scarab species that are less susceptible to nematod es and/or imidacloprid, This combination has a low environmental impact and high compatibility with natural biological control of turfgrass insects. T he possible roles of these combinations in augmentative control approaches are discussed. (C) 2000 Academic Press.