PREDATION AND BARK BEETLE DYNAMICS

Bark beetle populations may undergo dramatic fluctuations and are ofte n important pests in coniferous forests. Their dynamics are thought to be primarily driven by factors affecting the resistance of the host t ree to attack, i.e., bottom-up forces, while natural enemies are usual ly assigned a minor role in these systems. I present behavioral experi ments that suggest that the clerid beetle Thanasimus dubius may be an important source of mortality for the bark beetle Dendroctonus frontal is during attack of the host tree, and determine the nature of the fun ctional response of T. dubius under conditions close to natural. I als o examine the numerical response of T. dubius to large-scale fluctuati ons in D. frontalis density, and the relationship between bark beetle population trends and predator density, and find that beetle populatio ns tend to decline when predator densities are high. Combined with the effects of clerid larvae on bark beetle broods, these results suggest that top-down forces generated by natural enemies could also be an im portant component of bark beetle dynamics. The implications of these r esults for bark beetle dynamics are discussed in relation to the prolo nged life-cycle of clerid beetles.