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 a ttributed to the use of inappropriate nematode strains. We evaluated s everal species and strains of entomopathogenic nematodes (Heterorhabdi tidae and Steinernematidae) against chafer Cyclocephala hirta in a soi l and pot bioassay at 25 degrees C. The NJ65 strain of Steinernema gla seri, isolated from New Jersey, outperfonned all other steinermematid and heterorhabditid nematodes, resulting in a 76.5% lan al mortality w ithin 3 d of treatment at 125 nematodes per lava. After 6 days of trea tment, 4 strains of S. glaseri (NJ21, NJ29, NJ42, and NJ65) achieved 1 00% 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. Stein ernema anomali (Ryaznn), Steinernema kushidai (Hamakita), Heterorhabdi tis megidis (HOI),and H bacteriophora (HP88) caused only 45, 55, 60, a nd 66.7% larval mortality, respectively. Steinernema feltiae (Argentin a strain) caused only 16% larval mortality, and Steinernema carpocapsa e (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 degre es 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 .