Effects of endemic and released entomopathogenic nematodes on annual bluegrass weevil populations in golf course fairways

The annual bluegrass weevil (Listronotus maculicollis Kirby) (ABW) is a highly destructive pest of golf course turfgrass in the Northeastern United States. Turf managers primarily manage ABW with preventive applications of synthetic insecticides against the overwintered adults in spring. In an effort to develop less toxic management options for ABW, we investigated the impact of endemic and released entomopathogenic nematode (EPN) populations on ABW population dynamics. Field surveys between 2005 and 2007 demonstrated that two EPN species, Heterorhabditis bacteriophora and Steinernema carpocapsae, regularly infect many weevil stages and increase in density in response to increasing weevil densities. However, variable generational mortality and sensitivity to environmental extremes suggest that EPNs cannot reliably keep ABW populations below damage thresholds. Laboratory assays and field releases of commercial species of EPNs targeting fourth and fifth instar larvae have shown promise. In the laboratory, S. feltiae and S. carpocapsae demonstrated high levels of control of ABW larvae (97 and 100%, respectively). Fifth instar larvae were less susceptible than fourth instars, suggesting that application timing will be critical for effective control. Field trials using endemic and commercial EPN strains indicate that high control levels can be achieved with several species (S. feltiae, S. carpocapsae, H. bacteriophora). However, control was variable between trials and years and seemed to be greatly affected by ABW densities.