Effect of Host Size on Susceptibility of Melanotus communis (Coleoptera: Elateridae) Wireworms to Entomopathogens

Wireworms, the soil-borne larvae of click beetles (Coleoptera: Elateridae), are important crop pests throughout the world. In the eastern U.S., Melanotus communis larvae attack grain, root/ tuber, and vegetable crops. Our objectives were to characterize the pathogenicity and virulence of fungal and nematode entomopathogens on M. communis wireworms, and determine if wireworm size affected virulence. Pathogens tested included five entomopathogenic nematodes, Steinernema carpocapsae (All strain), S. feltiae (SN strain), S. riobrave (355 strain), Heterorhabditis bacteriophora (VS strain), and H. indica (HiHom1 strain); and two entomopathogenic fungi, Beauveria bassiana (GHA strain) and Cordyceps javanica (WF-GA17 strain). None of the pathogens tested caused >15% mortality at 7 or 14 days post-inoculation. Mortality was highest in S. carpocapsae (All strain); the other entomopathogens did not cause higher mortality than the untreated control. Overall, smaller wireworms were more susceptible than larger wireworms. Our results suggested that M. communis wireworms have defenses that limit the ability of the entomopathogens we tested to infect the wireworms. Conceivably, other entomopathogen strains or species may be more effective. Natural populations of entomopathogens may contribute to wireworm population reduction, but further studies are warranted before entomopathogens can be used for M. communis management.