Steinernema scarabaei for the control of white grubs

The efficacy of the new entomopathogenic nematode species, Steinernema scarabaei, isolated from white grubs in New Jersey for the control of economically important white grub species (Coleoptera: Scarabaeidae) was compared to that of two strains of Steinernema glaseri, four strains/isolates of Heterorhabditis bacteriophora (including two fresh isolates from scarab larvae), and an undescribed Heterorhabditis species from Korea. The efficacy was tested against the oriental beetle, Exomala (= Anomala) orientalis, the Japanese beetle, Popillia japonica, and the northern masked chafer, Cyclocephala borealis, under laboratory, greenhouse, and field conditions, and against the European chafer, Rhizotrogus majalis, in the laboratory. Under laboratory and greenhouse conditions, S. scarabaei was highly pathogenic to P. japonica, E. orientalis, and R. majalis, but was less effective against C. borealis. However, S. scarabaei provided excellent control of P. japonica, E. orientalis, and C. borealis under field conditions. P. japonica was the most nematode-susceptible white grub species. Against this species the superiority of S. scarabaei over the other nematodes tested became only apparent under field conditions and with very low nematode rates in the laboratory. C. borealis was less susceptible to all nematodes tested and only in a field experiment did S. scarabaei clearly outperform H. bacteriophora. Both E. orientalis and R. majalis were highly susceptible to S. scarabaei but showed moderate to low susceptibility to all other nematodes tested. In a field experiment, S. scarabaei also controlled P. japonica and E. orientalis larvae more quickly than H. bacteriophora. There was weak synergism between S. scarabaei and the neonicotinoid insecticide imidacloprid against E. orientalis larvae but not against P. japonica and C. borealis larvae. Overall, S. scarabaei shows exceptional potential for the biological control of white grubs.