Efficacy of entomopathogenic Heterorhabditis and Steinernema nematodes against the white grub, Leucopholis lepidophora Blanchard (Coleoptera: Scarabaeidae)

The white grub Leucopholis lepidophora Blanchard (Coleoptera: Scarabaeidae) is a serious pest of arecanut and other commercial crops in India. The development of an environmentally-friendly control method for this pest is urgently needed. The efficacy of two species of entomopathogenic nematodes (EPN), namely Steinernema abbasi Elawad and Heterorhabditis indica Poinar (Rhabditida: Steinernematidae and Heterorhabditidae) was evaluated against this pest in the laboratory and in arecanut fields. In the laboratory assays, H. indica caused significantly higher mortality rates (37.5-93.8%) than S. abbasi (22.5-75.0%) in second instar L. lepidophora larvae. Heterorhabditis indica caused 20.0-77.5% mortality and S. abbasi 12.5-65.0% mortality in third instar larvae. Significant differences were observed in LC50 and LC90 values of the nematode species against different life stages of L. lepidophora. Both nematode species and a standard insecticide (chlorpyrifos) were tested against this insect in two field experiments. Grubs were mainly in the second instar stage and third instar stage. Both laboratory and field experimental results indicated that second instar grubs were more susceptible to the nematode species tested than third instar grubs and that the efficacy of EPNs against L. lepidophora larvae varies with nematode species. In both the field experiments, H. indica (3.5 × 105 IJ palm−1) showed a significantly higher percentage mortality rate of the white grub larvae compared to that of S. abbasi and chlorpyrifos treatments. Chlorpyrifos application, however, was more effective in reducing the grub population compared to S. abbasi (1.7 × 105 IJ palm−1). Our results show that H. indica has good potential as an alternative management tool for the management of L. lepidophora in areacnut production.