Competition and intraguild predation between the braconid parasitoid Bracon hylobii and the entomopathogenic nematode Heterorhabditis downesi, natural enemies of the large pine weevil, Hylobius abietis

摘要

In biological control programmes introduced natural enemies compete withnindigenous enemies for hosts and may also engage in intraguild predation whenntwo species competing for the same prey attack and consume one another. The largenpine weevil, Hylobius abietis L. (Coleoptera: Curculionidae), is an important pest ofnconiferous reforestation in Europe. Among its natural enemies, the parasitoid Braconnhylobii Ratz. (Hymenoptera: Braconidae) and entomopathogenic nematodes havenpotential as biological control agents. Both parasitoid and nematodes target thenweevil larvae and, hence, there is potential for competition or intraguild predation.nIn this study, we examine the interaction of B. hylobii with the nematodenHeterorhabditis downesi Stock, Griffin and Burnell (Nematode: Heterorhabditidae),ntesting the susceptibility of larvae, pupae and adults of B. hylobii to H. downesi andnwhether female parasitoids discriminate between nematode-infected and uninfectednweevils for oviposition. In choice tests, when weevils were exposed tonnematodes 1–7 days previously, no B. hylobii oviposited on nematode-infectednweevil larvae. Up to 24 h, healthy weevils were twice as likely as nematodeinfectednones to be used for oviposition. Bracon hylobii females did not adjust clutchnsize; nematode-infected hosts were either rejected or the parasitoid laid a fullnclutch of eggs on them.nWhen nematodes were applied to the parasitoid feeding on weevil larvae, thennematodes parasitized the parasitoid larvae, there was a reduction in cocoonnformation and fewer cocoons eclosed. Eclosion rate was not reduced whennnematodes were applied to fully formed cocoons, but nearly all of the emergingnadults were killed by nematodes.