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

摘要

In biological control programmes introduced natural enemies compete with\udindigenous enemies for hosts and may also engage in intraguild predation when\udtwo species competing for the same prey attack and consume one another. The large\udpine weevil, Hylobius abietis L. (Coleoptera: Curculionidae), is an important pest of\udconiferous reforestation in Europe. Among its natural enemies, the parasitoid Bracon\udhylobii Ratz. (Hymenoptera: Braconidae) and entomopathogenic nematodes have\udpotential as biological control agents. Both parasitoid and nematodes target the\udweevil larvae and, hence, there is potential for competition or intraguild predation.\udIn this study, we examine the interaction of B. hylobii with the nematode\udHeterorhabditis downesi Stock, Griffin and Burnell (Nematode: Heterorhabditidae),\udtesting the susceptibility of larvae, pupae and adults of B. hylobii to H. downesi and\udwhether female parasitoids discriminate between nematode-infected and uninfected\udweevils for oviposition. In choice tests, when weevils were exposed to\udnematodes 1–7 days previously, no B. hylobii oviposited on nematode-infected\udweevil larvae. Up to 24 h, healthy weevils were twice as likely as nematodeinfected\udones to be used for oviposition. Bracon hylobii females did not adjust clutch\udsize; nematode-infected hosts were either rejected or the parasitoid laid a full\udclutch of eggs on them.\udWhen nematodes were applied to the parasitoid feeding on weevil larvae, the\udnematodes parasitized the parasitoid larvae, there was a reduction in cocoon\udformation and fewer cocoons eclosed. Eclosion rate was not reduced when\udnematodes were applied to fully formed cocoons, but nearly all of the emerging\udadults were killed by nematodes.