Effects of Entomopathogenic Nematodes on the Predator Calosoma granulatum in the Laboratory

Abstract

Entomopathogenic nematodes (EPNs) are used in inundative biological control of pests, such as Spodoptera frugiperda, which is targeted primarily when it enters the soil to form pupae. Within insects, EPNs require 7–15 days to form new infective juveniles (IJs); however, if the insect carcass is predated during this period, the population dynamics of nematodes and predators in the soil may be affected. In the soil, S. frugiperda is predated by carabid beetle Calosoma granulatum, which feeds on carcasses and living insects. The aim of the study was to analyze the direct effects of EPN contact with the predator and the effects of EPNs parasitizing prey on predator feeding. The predator C. granulatum and EPN H. amazonensis isolates RSC 5 and JPM 4, which have activity against S. frugiperda, were used. Laboratory experiments were conducted with topical application of IJs on the predator, as were experiments with and without choice using S. frugiperda larvae that were either healthy or infected by EPNs as prey. It was found that only the first instar predator larvae are susceptible to EPNs when applied topically at concentrations greater than 150 IJs/mL. The third instar larvae and adults avoid feeding on infected larvae, but the repulsion occurs only after symbiotic bacteria are released by EPNs inside the host. When predator only had access to infected carcasses as food, most larvae died during the 6 days of feeding. The results obtained shown that in general, these two native isolates of H. amazonensis, are safe for the native predator C. granulatum.