Interaction of entomopathogenic nematodes, Steinernema glaseri (Rhabditida: Steinernematidae), cultured in irradiated hosts, with ‘F1 sterility’: Towards management of a tropical pest, Spodoptera litura (Fabr.) (Lepidoptera: Noctuidae)

Abstract

Efficacy of the entomopathogenic nematode (EPN), Steinernema glaseri, (Steiner) cultured in radio-sterilized host, was studied vis-à-vis radiation-induced F1 sterility on a tropical lepidopteran pest, Spodoptera litura (Fabr.). To ensure safe transport of S. glaseri EPNs in vivo, host radio-sterilization was done; and the parasitising performance of S. glaseri infective juveniles (IJs), cultured in irradiated last instar S. litura larvae (with either 40 or 70 Gy of gamma rays) was evaluated on F1 sterile insects (progeny of male moths treated with 100 Gy, 130 Gy). S. glaseri EPNs cultured in radio-sterilized larvae at 40 Gy, had better infective potential than those cultured in sterilized host larvae at 70 Gy. F1 sterile larval hosts (progeny from 100 or 130 Gy treated parents) were equally acceptable to the EPNs cultured in radio-sterilized hosts, although the nematode harvest was reduced on F1 sterile hosts at 130 Gy. Infectivity of IJs derived from F1 sterile host was almost similar on F1 sterile larvae and normal larvae of S. litura, although their parasitisation efficacy on the F1 sterile hosts was relatively less than the controls. The IJs performance was little influenced by irradiation of IJs’ parent host and current host's irradiation history individually, but both the parameters together did not have any further negative interaction on the performance of IJs. The present results indicate that S. glaseri harvested from F1 sterile larval hosts (progeny from 100 or 130 Gy treated parents) retained a reasonably high degree of infectivity on normal and F1 sterile S. litura hosts (61–83% of controls). Two highly promising operational modes of integrating S. glaseri EPNs with ‘F1 sterility’ to suppress S. litura populations (initial releases of EPNs to strongly suppress the density of the pest followed by use of F1 sterility vs. simultaneous use of both techniques) are discussed.