Long-term effects and persistence of Steinernema scarabaei applied for suppression of Anomala orientalis (Coleoptera: Scarabaeidae)

Abstract

The entomopathogenic nematode, Steinernema scarabaei, is adapted to scarab larvae as hosts and has already shown exceptional potential for inundative control of these pests. To determine the long-term effects of S. scarabaei application on scarab populations and the nematode’s persistence, S. scarabaei was applied in mid-September at rates from 0.06 to 2.5 × 10 9 infective juveniles (IJs)/ha to turfgrass plots seeded with oriental beetle, Anomala orientalis, larvae. Scarab and nematode populations were monitored for 3–4 years thereafter. S. scarabaei provided excellent A. orientalis control (77–100%) within 1 month of application at rates of 0.25–2.5 × 10 9 (IJs)/ha and particularly in the following spring at rates of 0.1–2.5 × 10 9 (IJs)/ha (86–100%). S. scarabaei provided significant control in the next A. orientalis generation in two out of 10 treatments in fall (i.e., 13 months after application) and six out of 10 treatments in the following spring. Thereafter, significant control was only observed occasionally. S. scarabaei numbers were highly variable, and few significant differences among treatments were observed. S. scarabaei recovery from the treated plots was generally more consistent through the first spring after application and became more variable thereafter, but S. scarabaei was recovered for up to 4 years in the experimental plots. Endemic populations of Heterorhabditis bacteriophora and Steinernema carpocapsae, regularly recovered from the experimental plots and often in higher numbers than S. scarabaei, had no significant effect on A. orientalis densities but were able to coexist with S. scarabaei. Our observations suggest that, once current problems with its mass production can be overcome, S. scarabaei could be augmented periodically in areas with recurrent scarab infestations to provide long-term suppression.