Everard, A. and Griffin, C.T. and Dillon, A.B.
Competition and intraguild predation
between the braconid parasitoid
Bracon hylobii and the entomopathogenic
nematode Heterorhabditis downesi,
natural enemies of the large pine weevil,
Bulletin of Entomological Research, 99.
In biological control programmes introduced natural enemies compete with
indigenous enemies for hosts and may also engage in intraguild predation when
two species competing for the same prey attack and consume one another. The large
pine weevil, Hylobius abietis L. (Coleoptera: Curculionidae), is an important pest of
coniferous reforestation in Europe. Among its natural enemies, the parasitoid Bracon
hylobii Ratz. (Hymenoptera: Braconidae) and entomopathogenic nematodes have
potential as biological control agents. Both parasitoid and nematodes target the
weevil larvae and, hence, there is potential for competition or intraguild predation.
In this study, we examine the interaction of B. hylobii with the nematode
Heterorhabditis downesi Stock, Griffin and Burnell (Nematode: Heterorhabditidae),
testing the susceptibility of larvae, pupae and adults of B. hylobii to H. downesi and
whether female parasitoids discriminate between nematode-infected and uninfected
weevils for oviposition. In choice tests, when weevils were exposed to
nematodes 1–7 days previously, no B. hylobii oviposited on nematode-infected
weevil larvae. Up to 24 h, healthy weevils were twice as likely as nematodeinfected
ones to be used for oviposition. Bracon hylobii females did not adjust clutch
size; nematode-infected hosts were either rejected or the parasitoid laid a full
clutch of eggs on them.
When nematodes were applied to the parasitoid feeding on weevil larvae, the
nematodes parasitized the parasitoid larvae, there was a reduction in cocoon
formation and fewer cocoons eclosed. Eclosion rate was not reduced when
nematodes were applied to fully formed cocoons, but nearly all of the emerging
adults were killed by nematodes.
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