Maintenance of a Phloem-Inhabiting Guild

Abstract

A guild composed of bark beetles (Coleoptera: Scolytidae) and the southern pine sawyer, Monochamus titillator (F.) (Coleoptera: Cerambycidae), occurring in pine phloem was studied. The goal of this study was to examine interactions between bark beetles and M. titillator that may be involved in maintaining guild structure. M. titillator potentially can cause significant bark beetle mortality. Mortality to the bark beetles was low because the bark beetles had little direct contact with M. titillator. Dendroctonus frontalis Zimmermann larvae avoided M. titillator by migrating to the outer bark, whereas Ips avulsus (Eichhoff) and I. calligraphus (Germar) developed rapidly and emerged from the tree before the phloem was foraged heavily by M. titillator . The fact that the bark beetles have little direct contact with M. titillator is enough to maintain the bark beetles' presence in this guild. In contrast, commensalism, through the expansion of M. titillator's resource base caused by bark beetle activity, seems to be important in maintaining M. titillator's place.