Several factors that influence the activity of steinernematid and heterorhabditid nematodes against adult Japanese beetles were examined in the laboratory. The effect of nematode concentration on mortality of adult beetles was evaluated using a Petri plate bioassay. The adults were exposed to 1,000 to 10,000 infective stage juveniles (J3) of Steinernema glaseri per 10 beetles with or without food for 24 hr after which they were held with food for an additional 6 days. The LC50s for males with and without food during exposure were 3,435 and 2,854 J3s/10 adults, respectively. The LC50s for mixtures of males and females with and without food were 5,228 and 1,762 J3s/10 adults respectively. Although mortality occurred during and shortly after exposure, significant additional mortality was observed 1-4 days following exposure. Exposure of males and females with food to 10,000 J3s/10 adults for 6, 12, 18, or 24 hr resulted in 47, 58, 72, and 77 % mortality, respectively. Comparative activity of S. glaseri, S. carpocapsae (All strain), S.feltiae (Biosys experimental cold adapted strain = bibionis), S.feltiae (Biosys experimental strain 27), Heterorhabditis bacteriophora, and Heterorhabditis sp. (Terceiran isolate) was evaluated against adult Japanese beetles using a 24 hr exposure to 8,000 J3s/10 adults. The most virulent species were S. glaseri, S.feltiae (= bibionis), the Terceiran isolate of Heterorhabditis and S. carpocapsae producing 55, 44, 36 and 34 % mortality respectively. Our results indicate that adult Japanese beetles infected with entomopathogenic nematodes could serve as a mechanism for nematode dispersal.
