Effect of storage periods on survival and infectivity of indigenous entomopathogenic nematodes of insect pests of rice

Abstract

Laboratory investigations were carried out to study the survival and infectivity of two indigenous species of entomopathogenic nematodes (EPN), Rhabditis (Oscheius) sp. and Steinernema thermophilum, stored at room temperature for varying periods (5-150 days), on two insect hosts, greater wax moth, Galleria mellonella and rice moth, Corcyra cephalonica. Observations were made on per cent survival, time taken for mortality of host larvae as well as recovery of infective juveniles (IJs) of the two EPN species from the host cadavers. There was 100% survival of both species of EPN on the two hosts after storage for up to 50 days, but thereafter the survival of Rhabditis (Oscheius) sp. declined to zero and that of S. thermophilum to 10% after 150 days of storage. Both EPN species took more time to kill G. mellonella than C. cephalonica. Inoculation with Rhabditis (Oscheius) sp. stored for five days resulted in maximum recovery from G. mellonella, while there were no significant differences in recoveries of IJs from C. cephalonica. The IJs of S. thermophilum stored for 100 days took 20.8 h to kill G. mellonella, while those stored for 50 and 100 days took 19.6 to 25.6 h to kill C. cephalonica. The recovery of IJs of S. thermophilum was greater from G. mellonella (36033 to 49298/larva) than from C. cephalonica (24161 to 28154/larva). There were no significant differences in recoveries of IJs after storage at different periods from these two hosts.