Optimizing the use of entomopathogenic nematodes for the management of Listronotus maculicollis (Coleoptera: Curculionidae): Split applications and combinations with imidacloprid

Abstract

Entomopathogenic nematodes have shown potential as biocontrol agents targeting larvae of the annual bluegrass weevil, Listronotus maculicollis Kirby, a major golf course turf pest in eastern North America with widespread insecticide resistance. Control levels of single applications of nematodes have been too low and variable in the past to support application by golf course managers for weevil control. We examined if splitting nematode applications in two at half rates approximately 1 week apart as well as combinations of the nematodes with the neonicotinoid imidacloprid could improve nematode performance. In greenhouse experiments in pots with grass infested with ABW larvae, the entomopathogenic nematodes Steinernema carpocapsae, S. feltiae, and Heterorhabditis bacteriophora were similarly effective for larval control. Combination with imidacloprid resulted in additive weevil mortality. In a field experiment with natural infestations of larvae using 1.25 and 2.5 × 109 nematodes ha−1, respectively, of S. carpocapsae and H. bacteriophora, additive mortality in the combinations with imidacloprid amounted to 82% and 79% control, respectively, at the high nematode rate. In three additional field experiments using only S. carpocapsae, the low and high nematode rate provided on average 59% and 74% control, respectively, while their combinations with imidacloprid provided 75% and 84% control, respectively. Imidacloprid alone averaged 37% control. Mortality in all combination treatments was additive. Splitting S. carpocapsae applications provided a marginal increase in mortality that was significant only in one of three experiments. However, combining split applications with imidacloprid provided 88–95% control which could offer an effective alternative to synthetic insecticides.