Virulence of entomopathogenic nematodes to the western masked chafer Cyclocephala hirta (Coleoptera: Scarabaeidae)

Predictability is a key challenge in biological control of white grubs with entomopathogenic nematodes. Most field test failures have been attributed to the use of inappropriate nematode strains. We evaluated several species and strains of entomopathogenic nematodes (Heterorhabditidae and Steinernematidae) against chafer Cyclocephala hirta in a soil and pot bioassay at 25 degrees C. The NJ65 strain of Steinernema glaseri, isolated from New Jersey, outperfonned all other steinermematid and heterorhabditid nematodes, resulting in a 76.5% lan al mortality within 3 d of treatment at 125 nematodes per lava. After 6 days of treatment, 4 strains of S. glaseri (NJ21, NJ29, NJ42, and NJ65) achieved 100% larval mortality. Other strains that caused >80% larval mortality after 6 d of treatment included NJ32, NJ40 and NJ41 of S. glaseri, and Chino Hill, Merced, and Nebraska strains of Heterorhabditis sp. Steinernema anomali (Ryaznn), Steinernema kushidai (Hamakita), Heterorhabditis megidis (HOI),and H bacteriophora (HP88) caused only 45, 55, 60, and 66.7% larval mortality, respectively. Steinernema feltiae (Argentina strain) caused only 16% larval mortality, and Steinernema carpocapsae (AU and Mexican strains) and Steinernema scapterisci (Colon strain) were nonpathogenic to C. hirta. Steinernema riobracis caused no larval mortality at 25 degrees C, but inflicted 45-71% mortality at 30 degrees C. Our studies indicate that S.glaseri and Heterorhabditis spp, are most virulent among entomopathogenic nematodes toward C. hirta larvae and certain strains of S. glaseri are superior to Heterorhabditis spp.