SeMNPV reactivation through stress factors in covertly infected Spodoptera exigua

Abstract

The aim of this study is to evaluate the effect of different stress factors on covertly infected Spodptera exigua larvae in terms of virus reactivation. For this, adult survivors that had ingested occlusion bodies of S. exigua multiple nucleopolyhedrovirus (SeMNPV) were mated and the subsequent generation (F1) tested for virus reactivation in the second instar both in laboratory and field conditions. In the laboratory a number of treatments were tested including chemical stressors, inoculation with permissive and non permissive NPV species and Bacillus thuringiensis spores and crystals. Both, parental and F1 adults were confirmed to harbor the infection by qPCR. Reactivation was observed in 0.1% copper sulfate, 1% iron sulfate, and 1 ppm sodium selenate treatment that resulted in 12, 15, and 41% mortality due to SeMNPV, while no larvae with symptoms of viral infection were registered in virus-free controls. No effect on NPV-induced mortality was detected after inoculation with heterologous virus. Lately field trials were carried out by artificial infestation of pepper crops in experimental greenhouses using sublethally infected S. exigua larvae to evaluate copper sulfate and sodium selenate as activation factors. Hardly any NPV-induced mortality was observed in those larvae treated in field conditions.