SOIL INTERACTIONS WITH CHEMICAL INSECTICIDES AND NEMATODES USED FOR CONTROL OF JAPANESE-BEETLE (COLEOPTERA, SCARABAEIDAE) LARVAE

Mortality of last-instar Japanese beetles, Popillia japonica Newman, was highest when exposed to isazophos, bendiocarb, and chlorpyrifos in 30-ml arenas containing California soils in laboratory assays. Carbaryl and two nematodes, Heterorhabditis bactetiophora Poinar and Steinernema glaseri (Steiner), were less effective treatments in these arenas. Soil x treatment (insecticides and nematodes) interactions were highly significant, often changing larvicide rank order of efficacy within soils. Soil characteristics identified by regression analysis as affecting insecticidal activity were organic matter (chlorpyrifos, bendiocarb, and S. glaseri) and pH (carbaryl and isazophos). In arenas (7.6-cm diameter by 15 cm) simulating turf conditions, S. glaseri was the most effective treatment, followed by chlorpyrifos, then bendiocarb. The influence of irrigation on improving insecticide efficacy increased with higher soil organic matter. Because no treatment was completely effective against larvae, eradication of Japanese beetles cannot depend entirely on control tactics directed against the immature stages.