REDUCTION OF TESTIS GROWTH OF PSEUDALETIA-SEPARATA LARVAE AFTER PARASITIZATION BY COTESIA-KARIYAI

The braconid endoparasitoid, Cotesia (=Apanteles) kariyai physiologica lly influences its host, Pseudaletia separata, through three factors: polydnavirus, venom, and teratocytes. Inhibiting testis development of the host seems to be one factor that is important for successful deve lopment of the parasitoid. CkPV (polydnavi rus of Cotesia kariyar) plu s venom depressed testis development. Testes from unparasitized day 0 last instar transplanted into isolated abdomens increased in volume af ter stimulation with 20-hydroxyecdysone (20HE). However, day 0 testis preincubated with CkPV plus venom for 6 h and then transplanted into a n isolated abdomen did not respond to 20HE. Southern blot analysis ind icated CkPV-DNA hybridized to testes-DNA from parasitized hosts, sugge sting the possibility that CkPV is involved in suppression of testes g rowth. Binding assays using PNA indicated a 2-fold increase in ecdyste roid receptor binding activity during the late stage of parasitism. Th e increase in receptor activity might be related to the maintenance of a low ecdysteroid titer in parasitized hosts due to a feedback respon se, (C) 1994 Wiley-Liss, Inc.