none The development pathology of H. virescens larvae parasitized by the braconid wasp M. 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 normally are under the host's endocrine control. Neck ligation of control larvae was used to identify the critical periods in parasitized and unparasitized 4th- and 5th-instar larvae. Control ligated 4th-instar larvae apparently released PTTH (prothoracicotropic hormone) between 21:00 AZT (arbitrary zeitgeiber time) of the 2nd day of the instar and 1:00 AZT of the 3rd day. Parasitized 4th-instar larvae were smaller and apparently released PTTH between 18:00 and 23:00 AZT of the 3rd day. Control ligated 5th-instar larvae apparently released PTTH between day 1 and day 2 of the cell formation phase. Ligated 5th-instar parasitized larvae never molted to the pupal stage. Parasite larvae were affected adversely by host neck ligation with their pupal plus cocoon weight being proportional to the age of the host at the time of ligation.