Native entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) provide effective biocontrol against Oriental leafworm moth, Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) in cabbage

Abstract

The Oriental leafworm, Spodoptera litura, is a polyphagous pest that attacks several crops. In this study, we studied the susceptibility of the larval and pupal stages of S. litura to native entomopathogenic nematodes Heterorhabditis indica NBAIRH80, and S. surkhetense NBAIRS81. Bioassay results revealed that upon inoculating 400 infective juveniles (IJ) larva⁻¹ to fourth-instar S. litura larvae with H. indica and S. surkhetense, H. indica caused 100% mortality whereas S. surkhetense caused 54% mortality. When S. litura pupae were inoculated with 50 IJ of H. indica, the pupal mortality was only 10% when the IJ concentration was increased to 600 IJ pupa⁻¹, the pupal mortality also increased to 80%. The percentage mortality in larvae and pupae of S. litura increased significantly with increase in the exposure time. Both nematode species were able to penetrate into the S. litura larvae and also completed their life cycle by producing large numbers of IJ. Pot and field experiments showed that cabbage plants sprayed with H. indica and flubendiamide significantly reduced the number of larvae, leaf injury (H. indica: 0.7: 0–4 scale flubendiamide: 0.4: 0–4 scale), head injury (H. indica: 0.5: 0–4 scale flubendiamide: 0.6: 0–4 scale) and increasing yield (H. indica: 23.57 tonnes ha⁻¹ flubendiamide: 25.53 tonnes ha⁻¹). These results showed that, H. indica performed equally well that of flubendiamide. Overall results showed that H. indica NBAIRH80 can be incorporated in integrated pest management programme for S. litura.