Evidence for serine protease inhibitor activity in the ovarian calyx fluidof the endoparasitoid Venturia canescens

Endoparasitic wasps are able to develop inside permissive host insects due to their ability to overcome or evade the host's immune system. In the pres ent study, we provide experimental evidence that ovarian calyx fluid of the ichneumonid endoparasitoid Venturia canescens has the potential to alter h ost haemocyte spreading and inhibit host haemolymph melanisation due to the presence of a putative serine protease inhibitor (serpin) activity. The ex istance of a serpin-like activity in the calyx fluid is also supported by e xperiments where the synthetic protease inhibitor p-APMSF had effects on ce llular and cell-free immune reactions similar to ovarian calyx fluid. In ad dition, based on proteolytic digestion patterns of a wasp egg surface prote in, we predict an Arg-specific trypsin-like protease activity in the host h aemolymph which is possibly affected by calyx fluid components as well. Our data suggest that ovarian calyx fluid, deposited into the host together wi th the parasitoid egg, contains serpin activity which might transiently ina ctivate host defence reactions until other means of protection are establis hed on the egg surface. (C) 2000 Elsevier Science Ltd. All rights reserved.