Efficacy of indigenous entomopathogenic nematodes from Meghalaya, India against the larvae of taro leaf beetle, Aplosonyx chalybaeus (Hope)

The efficacy of three entomopathogenic nematode (EPN) species, Heterorhabditis indica, Steinernema thermophilum, and S. glaseri, from Meghalaya, India was studied against the larvae of taro leaf beetle, Aplosonyx chalybaeus (Hope) (Coleoptera: Chrysomelidae), under the laboratory conditions. The beetle larvae (grubs) were exposed to 25, 50, 75, 100 and 200 infective juveniles (IJs) of each nematode species for different time periods and they were found to be susceptible to all the EPNs tested. However, the susceptibility of grubs to nematode infection varied according to the dosages of IJs and their exposure periods. Appreciably good performance was achieved by S. glaseri, which showed 100 % mortality of insect larvae in 48 h exposure time. At 48 h of incubation, its LC₅₀ value was 90.3 IJs/larva, which was lower than that of S. thermophilum (115.0 IJs/larva) and H. indica (186.0 IJs/larva), at the same exposure time. All the tested nematode species were also found to reproduce within the host and produced infective juveniles. H. indica, however, showed comparatively more production of IJs per cadaver of infected host (168.9 × 10³ IJs/larva), as compared to the other two tested nematode species. The production of IJs per cadaver of infected host by S. thermophilum was recorded to be 82.0 × 10³ IJs/larva. In case of S. glaseri, while production of IJs increased initially to 18.9 × 10³ IJs/larva at concentration of 100 IJs/larva, it declined thereafter to 14.7 × 10³ IJs/larva at the dose of 200 IJs/larva. In conclusion, the evidence obtained in this study suggests that all the three indigenous EPN species are virulent enough to produce 100 % mortality in the last instar larvae of A. chalybaeus. These EPN species thus have potential scope for the management of A. chalybaeus in taro crops.