Impact of multiple natural enemies attacking a common, phloeophagous herbivore in a restricted habitat: Sequence, behaviour, and interactions

Field and laboratory assays were conducted to examine the attraction and impact of various natural enemies on bark beetle prey. More than eighty species from three orders were obtained arriving at and/or reproducing in trees colonized by Ips pini (Coleoptera: Scolytidae). Ips pini was most abundant during late summer. Medetera bistriata (Diptera: Dolichopodidae) was abundant and arrived concurrently with the herbivore. Exclusion of insects during the first two weeks of colonization decreased reproduction of I. pini and other wood borers in the spring, but not summer.; The relative preferences of Thanasimus dubius (Coleoptera: Cleridae) and Platysoma cylindrica (Coleoptera: Histeridae) to frontalin and ipsdienol were examined. Thanasimus dubius was attracted to both frontalin plus α-pinene and ipsdienol, but more strongly to the former, suggesting a historic association with Dendroctonus rufipennis (Coleoptera: Scolytidae). Platysoma cylindrica was only attracted to ipsdienol. Ips grandicollis, but not I. pini, was attracted to frontalin plus α-pinene.; In laboratory assays, P. cylindrica fed on all stages of I. pini. Adults exploited the herbivore's gallery architecture to facilitate adult capture. Larvae fed on I. pini larvae. Predatory behaviour of larval M. bistriata on I. pini larvae suggested likely involvement of a toxin.; In a laboratory assay, both predation by T. dubius and intraspecific competition decreased I. pini reproduction. The per capita effect of predation was approximately 4x greater than competition.; In a laboratory assay simulating field arrival patterns, increased predation on males was a significant cost of cheating, i.e., responding to pheromones but not engaging in host-searching. Thanasimus dubius affected the distribution of females per male.; Two laboratory assays with varying predator and prey densities were performed to investigate individual and combined effects of T. dubius and P. cylindrica on I. pini. Predators decreased I. pini reproduction on a total, per male, and per female basis. Predator reproduction suffered from high intraspecific interference, but interspecific intraguild predation appeared inconsequential. Thanasimus dubius and P. cylindrica were substitutable. Total emergence of the herbivore increased asymptotically with density. The proportional impact of predators decreased with increased herbivore colonization densities, suggesting that predator dilution is a benefit of group colonization.