White grub and nematode population dynamics after application of Steinernema scarabaei for white grub management

The entomopathogenic nematode Steinernema scarabaei has outstanding potential for curative control of many white grub species. High virulence and close adaptation to white grubs make it an excellent candidate for inoculative biological control. In three field studies, different rates of S. scarabaei were applied in mid-September to white grub population consisting primarily of oriental beetle, Anomala orientalis. White grub and nematode populations were observed for 4 years. Observations indicated that S. scarabaei reproduced very well in white grubs and that the emerging nematode progeny provided additional control. One month after application, rates as low as 0.25 × 109 S. scarabaei /ha (10% of regular field rate for nematodes) provided 77–100% control. S. scarabaei provided additional control in the following spring (86–100% at 0.1 to 2.5 × 109 S. scarabaei /ha). S. scarabaei persisted in all treated plots for at least 2 years and was recovered in many plots for 4 years. White grub suppression followed a similar pattern with no significant differences among S. scarabaei rates after the first year. White grub suppression was 62–92% 1 year after application but became more variable thereafter with 0–94%, 0–88%, and 0–100% at 2, 3, and 4 years after application.