Infection efficiency of Steinernema feltiae (DD-136) to the common cutworm, Spodoptera litura (Lepidoptera: Noctuidae) on the soil

Under suitable moisture and temperature conditions of soil for the mobility and infection of Steinernema feltiae (DD-136), infection efficiency on the common cutworm, Spodoptera litura, was investigated. With the decrease in inoculum size of nematodes from 1, 000 to 10 per 10 g soil in a petri dish (6 cm in inner diam.), there was an increase in the number of insects dying after their development to spinning larvae, prepupae or pupae. About 50% of the insects were infected after being exposed for 1 hr on soil inoculated with ca. 1, 000 infective juveniles, and 100% mortality was recorded for insects exposed 6 hr or longer. With increasing exposure on the nematode-inoculated soil, mortality of S. litura larvae rapidly decreased. Nematode infectivity also decreased with increasing inoculation depth, especially when inoculation was 44 mm or more below the surface. Spinning larvae, prepupae, and two-day old or younger pupae in the cell were infected, while three-day old pupae were not infected by the nematode. Longevity of infected moths became significantly shorter. Infection might have occurred during emergence from the nematode-inoculated soil.