Developmental pathology of Heliothis virescens larvae parasitized by Microplitis croceipes: Parasite‐mediated host developmental arrest

Abstract

AbstractThe developmental pathology of Heliothis virescens larvae parasitized by the braconid wasp Microplitis croceipes was examined. Parasitized host larvae begin the same precise sequence of developmental events in preparation for pupation as observed in unparasitized larvae. This sequence is initiated even though the host larval weight is below the normal developmental threshold for larval‐pupal transformation. After parasite emergence, the host remains in a suspended advanced developmental state but never pupates. The developmental parameters altered by parasitization are normally under the host's endocrine control.Neck ligation of control larvae was used to identify the critical periods in parasitized and unparasitized fourth‐ and fifth‐instar larvae. Control ligated fourth‐instar larvae apparently released PTTH between 21:00 AZT of the second day of the instar and 1:00 AZT of the third day. Parasitized fourth‐instar larvae were smaller and apparently released PTTH between 18:00 and 23:00 AZT of the third day. Control ligated fifth‐instar larvae apparently released PTTH between day 1 and day 2 of the cell formation phase. Ligated fifth‐instar parasitized larvae never molted to the pupal stage. Parasite larvae were adversely affected by host neck ligation with their pupal plus cocoon weight being proportional to the age of the host at the time of ligation.