Assessment of infective behaviour and reproductive potential over successive generations of entomopathogenic nematodes, Steinernema glaseri (Rhabditida: Steinernematidae), reared within radiosterilized host larvae, towards Spodoptera litura (Lepidoptera: Noctuidae)

Abstract

The infective behaviour of entomopathogenic nematodes (EPNs), Steinernema glaseri (Steiner), reared within radiosterilized host larvae of the tropical pest, Spodoptera litura (Fabricius), was ascertained towards the unirradiated same host (S. litura) for successive generations and compared with the infectivity of controls (EPNs derived from unirradiated host larvae). A primary goal was to establish a safe mode of transport and dispersal of EPNs without concern that uninfected, reproductively competent hosts would be inadvertently released. Based on prior studies on radiation-mediated effects, two gamma doses (40 and 70 Gy), were used for radiosterilization of last instar S. litura larvae. Tests were performed using the following parameters: Regimen I (Control) with normal infective juveniles (N-IJs) vs. normal (N) hosts; Regimen II with N-IJs vs. Irradiated hosts; Regimen III with F1 IJs (harvested from Regimen II) vs. N-hosts; and Regimen IV with F2 IJs (harvested from Regimen III) vs. N-hosts. The infective performance of F1 IJs was affected more at 70 Gy than at 40 Gy, but the effect was not great enough to nullify the infective efficiency of IJs emerged from irradiated hosts; thus, these IJs could be effectively utilized in pest biocontrol. Furthermore, the infective performance of F2 IJs was almost equivalent to that of the controls, especially at 40 Gy. Hosts radiosterilized at 70 Gy could be considered safer than those exposed to 40 Gy for inundative release of EPNs as biocontrol agents. Hosts radiosterilized at 40 Gy or 70 Gy could be conveniently used, with greater efficiency at 40 Gy, for inoculative release of EPNs for long-term pest management.