Potential of Heterorhabditis bacteriophora Poinar [Nematoda, Heterorhabditidae] in parasitizing Spodoptera litura Fabricius in response to malathion treatment

Activity of infective juveniles of Heterorhabditis bacteriophora in pre- and post-parasitic phases was studied vis-a-vis malathion treatment. The vitality of dauers (J₃) was ascertained subsequent to exposure to various sublethal concentrations of malathion (incorporated into nematode rearing medium). At concentrations of 200 and 400 ppm, the dauers showed behavioural disruptions as indicated by incomplete undulations. Anterior half of the treated dauers were mainly involved in performing undulations as compared with the posterior half. Lower concentrations showed transient effects. Infectivity tests were conducted using filter paper bioassay. The parasitization rate in Spodoptera litura larvae (L₆) decreased with increasing concentrations of malathion. Post-parasitic juveniles were examined daily for assessing the viability of H. bacteriophora after the treatment of malathion. Because of the cogent infectivity after malathion-exposure, it is suggested, that this nematode might be used as an agent in IPM. It appears a promising candidate.