OVERVIEW OF PARASITISM ASSOCIATED EFFECTS ON HOST HEMOCYTES IN LARVALPARASITOIDS AND COMPARISON WITH EFFECTS OF THE EGG-LARVAL PARASITOID CHELONUS-INANITUS ON ITS HOST SPODOPTERA-LITTORALIS

In the first part we review the effects of larval endoparasitoids and their polydnavirus and venom on the immune system of their hosts. In a ll systems investigated, haemocyte spreading and encapsulation activit y was reduced; in some cases effects on total (THC) or differential (D HC) haemocyte count as well as modification of haemocyte morphology an d ultrastructure were also documented. In many cases polydnavirus (and venom) were shown to play a major role in abrogation of the host's im mune reaction. In the second part we present the first investigation o f effects of parasitism and polydnavirus!venom on the immune system of the host for an egg-larval parasitoid, Chelonus inanitus. We observed that in 4th and 5th instar larvae, i.e. 7 to 10 days after parasitiza tion, neither haemocyte spreading and encapsulation activity, nor DHC, nor haemocyte ultrastructure were altered. After parasitization with X-ray irradiated wasps, which inject polydnavirus and venom and infert ile eggs, there was no alteration of the above mentioned parameters. N evertheless, parasitoid larvae implanted into 4th instar larvae which developed from eggs parasitized with X-ray irradiated wasps were not e ncapsulated, whereas co-injected latex beads were. These results show that parasitism by this egg-larval parasitoid does not generally suppr ess the host's immune system but that polydnavirus/venom injected at o viposition prevent, by, as yet unknown mechanisms, encapsulation of th e parasitoid larva. (C) 1998 Elsevier Science Ltd. All rights reserved .