Evaluation of two endemic and five commercial entomopathogenic nematode species (Rhabditida: Heterorhabditidae and Steinernematidae) against annual bluegrass weevil (Coleoptera: Curculionidae) larvae and adults

The annual bluegrass weevil, Listronotus maculicollis, is a highly destructive pest of golf course turfgrass in the northeastern United States. We assessed the virulence of entomopathogenic nematodes to larvae and adults of L. maculicollis as an initial step in developing a biological control program for this pest. Two endemic and five commercially available nematode species were tested in soil and field infested turf core assays. Adult susceptibility was generally low to moderate (11–65% mortality) and was not affected by the age or overwintering condition of the insect. A mixture of two nematode species with different foraging behaviors (Steinernema carpocapsae and Heterorhabditis bacteriophora) achieved the highest levels of adult control, but required 6 days to obtain 50% mortality at five times standard field application rate (125 nematodes/cm2). Conversely, fourth- and fifth-instar larvae were highly susceptible to nematodes. Steinernema feltiae, S. carpocapsae, and S. kraussei significantly reduced fourth instars in both years of the study. The same three species along with the commercial strain of H. bacteriophora significantly reduced high densities of fifth instars to below field damage thresholds. In general, Steinernema spp. trended towards greater control than Heterorhabditis spp. for both fourth and fifth instars. No difference was observed among the virulence of endemic and commercial nematode strains to any L. maculicollis stage tested. The data indicate that Steinernema spp. could provide high levels of control when applied curatively against L. maculicollis larvae.