The use of meconia to nondestructively detect sublethal infections in heliothines (Lepidoptera: Noctuidae)

The utility of using meconia to nondestructively detect entomopathogens of lepidopterous heliothines was examined. Early-instar tobacco budworm [Heliothis virescens (F.)] or cotton bollworm [Helicoverpa zea (Boddie)] larvae were inoculated with cytoplasmic polyhedrosis virus (CPV), Serratia marcescens Bizio, or Nosema heliothidis Lutz and Splendor, and the presence of each of the entomopathogens in adults and the meconia discharged during adult eclosion was determined. As the dose of CPV occlusion bodies and N. heliothidis spores but not S. marcescens cells ingested by larvae increased, a greater number of both adults and meconia were infested with the entomopathogens. For all three entomopathogens, no difference was observed between males and females for any of the parameters tested. The accuracy of the meconium method for predicting the presence of the entomopathogens in the adults (i.e., number of individuals in which meconia and adults were both positive, or meconia and adults were both negative) was > or = 92% for CPV, and > or = 79% for S. marcescens and N. heliothidis. Very few false negative predictions (i.e., the meconium was negative but the adult was positive) were observed for CPV (< or = 1%). The prevalence of false negative predictions ranged from 2 to 9%, and 5 to 21% for S. marcescens and N. heliothidis, respectively. The prevalence of false positive predictions (i.e., the meconium was positive but the adult was negative) was < or = 7% for CPV, < or = 13% for S. marcescens, and 0% for N. heliothidis. The results of this study demonstrate that although not absolute, the meconium method will be an efficacious method to detect nondestructively entomopathogens causing sublethal infections in heliothines, and possibly other insects, and thereby facilitate the rearing of specific pathogen free insects.