Pyrethroid resistance affects the efficacy of entomopathogenic nematodes for the control of annual bluegrass weevil larvae

The annual bluegrass weevil (ABW), Listronotus maculicollis, is a serious golf course pest in North America. Entomopathogenic nematodes (EPNs) Steinernema carpocapsae, S. feltiae and Heterorhabditis bacteriophora provide acceptable control (50-80%) of ABW larvae in golf course fairways. But golf turf managers prefer to use more consistent and effective synthetic insecticides. But 20% of golf courses battling ABW have populations resistant to various synthetic insecticides, particularly pyrethroids. Against resistant populations, EPNs might find wider use. In two field tests against larvae of a moderately pyrethroid resistant (55x) population we found similar control levels by S. carpocapsae, S. feltiae, and H. bacteriophora as against a non-resistant population. In greenhouse studies, control levels by these EPNs were around 15% lower against the 55x resistant population than a susceptible population for the same three EPNs. In another greenhouse experiment, S. carpocapsae provided 81% and 79% control of two pyrethroid-susceptible populations, but only 46-50% control of 100x and 343x resistant populations. In field tests against ABW populations with 55x-, 100x-, and 343x-pyrethroid resistance levels, respectively, S. carpocapsae provided 59, 63, and 45% control whereas S. riobrave provided 19, 28, and 46% control. Our findings suggest that efficacy of some EPN species may be negatively affected by high levels of pyrethroid-resistance in ABW. Future studies will examine if the elevated detoxification enzyme levels in resistant ABWs interfere with the EPN infection process.