Assemblage of Hymenoptera arriving at logs colonized byIps pini(Coleoptera: Curculionidae: Scolytinae) and its microbial symbionts in western Montana

Abstract

AbstractColonization of a tree by bark beetles and their symbionts creates a new habitat for a diverse assemblage of arthropods, including competing herbivores, xylophages, fungivores, saprophages, predators, and parasitoids. Understanding these assemblages is important for evaluating nontarget effects of various management tactics and for subsequently evaluating how changes in climate, the presence of invasive species, and altered forestry practices and land-use tenure may affect biodiversity. We characterized the assemblage of hymenopterans attracted to logs of ponderosa pine (Pinus ponderosaC. Lawson (Pinaceae)) colonized by the bark beetleIps pini(Say) and its microbial symbionts. In one experiment, the composition and relative abundances of species arriving at hosts colonized byI. pini, and possible sources of attraction, were determined. Treatments consisted of a log containingI. piniwith its natural complement of microorganisms, a log alone, and a blank control. A second experiment was carried out to determine whether or not Hymenoptera were attracted to microbial symbionts ofI. pini. Treatments consisted of a blank control, a log alone, a log containingI. piniwith its natural complement of microorganisms, eitherOphiostoma ips,Burkholderiasp., orPichia scolyti, and a log inoculated with a combination of these three microorganisms. Over 2 years, 5163 Hymenoptera were captured, of which over 98% were parasitoids. Braconidae, Platygastridae, Encyrtidae, Pteromalidae, and Ichneumonidae were the most abundant. Seven known species of bark beetle parasitoids (all Pteromalidae) were captured. However, parasitoids of Diptera, Lepidoptera, Hymenoptera, and non-wood-boring Coleoptera were also common. Nineteen species showed preferential attraction to host plants infested withI. piniand its complement of microorganisms, host plants inoculated withI. pinimicrobial symbionts, or host plants alone. Interestingly, many of these species were parasitoids of phytophagous, fungivorous, and saprophytic insects rather than of bark beetles themselves. These results suggest that a diverse assemblage of natural enemies that attack various feeding guilds within a common habitat exploit common olfactory cues.