Influence of brood hosts on host preferences of bark beetle parasites

Abstract

The southern pine beetle, Dendroctonus frontalis Zimmerman (SPB) is attacked by several species of hymenopterous parasites^1,2 the most common of which also parasitise other bark beetles^3–5 including the engraver beetles Ips grandicollis (Eichhoif), I. avulsus (Eichhoff), I. calligraphus (Germar), I. pini (Say); and the eastern juniper bark beetle, Phloeosinus dentatus (Say). The increasing importance of pest management has focused attention on the role of their natural enemies. However, the dynamics of bark beetle parasite populations is not generally known beyond estimates of mortality caused by parasites. The hymenopteran parasite guild of D. frontalis may kill up to 30% of a given brood². Since D. frontalis is cyclic in most areas with epidemics followed by very low population densities¹, other beetle hosts probably act as reservoirs for certain species of these parasites³. Conversely, during D. frontalis epidemics, other beetles, such as I. grandicollis and P. dentatus may compete as alternate hosts. Information on preferences for D. frontalis and other associated bark beetles is necessary to understand the interactions of this host–parasite complex. We report here the results of a study designed to determine if several known D. frontalis parasites display any host preferences among D. frontalis, I. grandicollis or P. dentatus.