PHYSIOLOGICAL AND ENDOCRINE CHANGES ASSOCIATED WITH POLYDNAVIRUS VENOM IN THE PARASITOID-HOST SYSTEM CHELONUS-INANITUS SPODOPTERA-LITTORALIS/

As shown earlier, parasitization by the egg-larval parasitoid C. inani tus causes in its host the precocious onset of metamorphosis in the 5t h instar followed by developmental arrest in the prepupal stage. Polyd navirus/venom were shown to be responsible for the developmental an es t. We investigated how polydnavirus/venom affect growth of the host la rvae and found that head capsule widths were smaller from the 4th to 6 th stadium and weights were lower in the 6th stadium in polydnavirus/v enom-containing larvae than in non-parasitized larvae. In an attempt t o identify endocrine parameters that are modified by polydnavirus/veno m and might be responsible for the developmental arrest in the prepupa , we compared juvenile hormones, juvenile hormone esterase and ecdyste roids between non-parasitized and polydnavirus/venom-containing larvae from the 4th instar until pupation or developmental arrest, respectiv ely. Obvious differences became manifest only in the 6th instar at the pupal cell formation stage, i.e. 12 days after entry of polydnavirus/ venom into the host egg. Then, prothoracic glands of polydnavirus/veno m-containing larvae released less ecdysteroids and ecdysteroid titres were lower than in non-parasitized larvae; this was followed by a dela yed, reduced and desynchronized increase in prepupal juvenile hormones and juvenile hormone esterase and a slightly modified metabolism of e cdysone. This indicates that polydnavirus/venom affects the endocrine system of the host only after pupal commitment and that inhibition of prothoracic gland activity is the first detectable effect. (C) 1998 El sevier Science B.V. Published by Elsevier Science Ltd. All rights rese rved.