Behavior of adult and larval Platysoma cylindrica (Coleoptera: Histeridae) and larval Medetera bistriata (Diptera: Dolichopodidae) during subcortical predation of Ips pini (Coleoptera: Scolytidae)

The most abundant predators of the pine engraver, Ips pini (Say), include Platysoma cylindrica (Paykull) and Medetera bistriata Parent. We amended "bark sandwiches" with pine engravers and adult P. cylindrica and larval M. bistriata, and report observations on these endophytic predators. Adult P. cylindrica preferred adult prey, and appeared to be facultative egg predators, which contrasts with other Histeridae. The larvae of P. cylindrica fed on pine engraver larvae. Protection from predators is generally assumed to be an advantage of an endophytic life history, but we found that this predator exploited the herbivore's gallery architecture to facilitate prey capture. Larval M. bistriata also fed on pine engraver larvae. Immediate paralysis or death of the prey followed a strike with their tentorial rods. Such rapid immobilization, in conjuction with the glandular histology of Medetera spp., suggests that they use a toxin to arrest prey.