Competition and intraguild predation between the braconid parasitoidBracon hylobiiand the entomopathogenic nematodeHeterorhabditis downesi, natural enemies of the large pine weevil,Hylobius abietis

Abstract

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.

Host activity and wasp experience affect parasitoid wasp foraging behaviour and oviposition on nematode‐infected larvae of the forestry pest Hylobius abietis

“…This indicates that it was the additional vibrational cues, rather than volatile cues that were responsible for the increased probability of B. hylobii females locating and then parasitising chewing hosts at short range. In summary, we conclude that vibrational cues generated by moving and/or feeding hosts are of significant importance in short-range host location and possibly also host acceptance by B. hylobii, as speculated by Henry & Day (2001) and Everard et al (2009). Although feeding-associated volatiles released from chewed bark appeared to have little importance for short-range host location in our trials, the bark in our trials was chewed on for 24 h at most, so we cannot rule out the possibility that volatiles emitted from a substrate that has been chewed or fed on for longer and under natural conditions may contribute to B. hylobii host-finding to a greater extent.…”

“…• C and under constant illumination as B. hylobii females are inactive in the dark (Henry & Day, 2001;Everard et al, 2009 …”

“…Everard et al (2009) reported that B. hylobii parasitised larvae of H. abietis infected with H. downesi less frequently than healthy hosts as early as 12 h after infection when given a choice between the two. However, it is unclear if wasps were actively rejecting infected hosts after locating them or if infected hosts were located less frequently than healthy hosts.…”

Behaviour and Population Dynamics of Entomopathogenic Nematodes Following Application

“…EPN compete with parasitoids for hosts or attack and kill susceptible stages of parasitoid, an example of intraguild predation (Rosenheim, Kaya, Ehler, Marois, & Jaffee, 1995). Ectoparasitoids are susceptible to nematode infection throughout larval development, but frequently become inaccessible at cocoon stage (Everard, Griffin, & Dillon, 2009;Lacey, Unruh, & Headrick, 2003), while endoparasitoids are susceptible for a shorter period, between emerging from the host and completing the cocoon (Kaya, 1978;Kaya & Hotchkin, 1981;Shannag & Capinera, 2000). In addition, parasitoid death due to premature nematode-induced host death has been reported in several laboratory studies.…”

“…In addition to killing individual parasitoids, nematodes might negatively impact on parasitoid populations if the female parasitoid lays her eggs on nematode-infected weevils where they are unable to complete their development. However, female parasitoids tend to avoid hosts that have been infected by EPN (Everard et al, 2009;Lacey et al, 2003;Sher, Parrella, & Kaya, 2000). Females of two ichneumonid species detected and avoided codling moth larvae as little as 12 h after treatment of the host with IJs (Lacey et al).…”