Effect of temperature and soil moisture on the infectivity of four species of entomopathogenic nematodes (Steinernema and Heterorhabditis spp.) to fall armyworm, Spodoptera frugiperda (Smith)

Spodoptera frugiperda (JE Smith) is one of the most important lepidopterous pests of maize throughout the word. The implementation of management strategies for this are need of the hour. In this case the use of Entomopathogenic nematodes (EPNs) is feasible because third-instar larvae feed in the leaf whorls of maize, and sixth instar larvae pupate in the soil; these two environments are congenial for the EPNs. But temperature and soil moisture play major roles in EPNs infectivity. Therefore, in the current study, we examined temperature and soil moisture effect on the infectivity of four indigenous EPN species from India, Heterorhabditis indica NBAIIH23, H. bacteriophora NBAIRH75, Steinernema carpocapsae NBAIRS59, and S. abbasi NBAIISa01 against larvae and pupae of S. frugiperda. Present study results showed that both temperature and soil moisture affected the infectivity of H. indica, S. carpocapsae, H. bacteriophora, and S. abbasi. As the exposure time increased, all these four nematodes infectivity to larvae was increased. Six days after inoculation, H. indica caused significantly higher larval mortality (96 %) at 25 degrees C and 100 % mortality at 28 degrees C. Whereas, S. carpocapsae caused 100 % mortality at 28 degrees C, and 76 % mortality at 25 degrees C. At 32 degrees C, H. indica and S. carpocapsae caused 90 % and 92 % larval mortality, respectively. As the temperature decreased to 20 degrees C, the infectivity of both the nematodes decreased. However, H. bacteriophora and S. abbasi caused 68 % and 50 % mortality in larvae at 20 degrees C, respectively. Compared to other nematodes, H. indica significantly caused higher mortality in pupae at 13 % soil moisture at 28 degrees C. We conclude that, Heterorhabditis indica and S. carpocapsae can be utilized against S. frugiperda larvae at (25-32 degrees C), and pupae at (28 degrees C). These nematodes can also be used against pupae of S. frugiperda at 9-13 % soil moisture content. We also suggest that these EPNs species can be incorporated in the Integrated Pest Management (IPM) for S. frugiperda.