As a group, arthropod natural enemies have been shown to substantially reduce within-tree pine bark beetle populations. However, little is known about the impacts of individual species on bark beetle mortality. In a controlled laboratory study, we measured the effects of two predaceous histerid species, Platysoma parallelum (Say) and Plegaderus transversus (Say), on Ips calligraphus (Germar) and Ips grandicollis (Eichhoff) brood mortality. Platysoma parallelum was found to have a greater impact on I. grandicollis mortality than Ple. transversus when only one histerid and prey species were present. No significant differences in I. calligraphus mortality were observed for either of the two histerid species. More I. grandicollis brood was killed per introduced Pla. parallelum adult than per introduced Ple. transversus adult likely as a result of the larger size and biomass requirements of Pla. parallelum. The results of this experiment indicate that histerids, by themselves, have the ability to lower within-tree bark beetle populations and could have potential use in a bark beetle biological control program.
