Parasitism of Lacanobia oleracea (Lepidoptera) by the ectoparasitoid, Eulophus pennicornis, is associated with a reduction in host haemolymph phenoloxidase activity

When haemolymph from fifth instar Lacanobia oleracea was incubated in vitro , rapid melanization occurred. Similar levels of melanization occurred in h aemolymph from larvae that had been experimentally injected with venom from the ectoparasitic wasp, Eulophus pennicornis. In contrast, haemolymph from larvae parasitized by this wasp melanized more slowly and less L extensive ly. Phenoloxidase assays indicated that enzyme activity was present in haem ocyte lysate supernatants, serum and plasma from L. oleracea and that on da y 5 post-parasitization, fractions prepared from parasitized larvae had sig nificantly less phenoloxidase activity than similar fractions from untreate d or experimentally envenomated larvae. In addition, no PO activity was det ectable in wasp venom, and the venom had no effect on L. oleracea plasma ph enoloxidase activity in vitro. These results indicate that parasitism of L. oleracea by E. pennicornis suppresses host haemolymph phenoloxidase activi ty and that this suppression is not induced by adult wasp venom. The result s are discussed with reference to the survival advantages of suppressing th e activity of this host enzyme, and to the possible source(s) of putative s uppressive factors. Crown copyright (C) 2000 Published by Elsevier Science Inc. All rights reserved.