Interspecific interactions among two foundation bark beetles

Interspecific interactions among tree-killing bark beetles species may have ecologically important consequences on beetle population dynamics and the distribution of host pines. We performed observational field surveys and species-ratio manipulation experiments using two tree-killing beetle species (Dendroctonus brevicomis and D. frontalis). Our objectives were to verify cross-attraction and co-colonization by beetles under field conditions in northern Arizona, and test the effects of gallery density and species ratio on response variables of average gallery length, offspring size (progeny fitness), and offspring per cm gallery (fecundity) for each species. Our field surveys indicate that heterospecific beetles aggregate to pheromones synthesized de novo by D. brevicomis under field conditions, and that oviposition galleries of both D. brevicomis and D. frontalis occurred together in the same region of host trees with significant frequency. Our species-ratio manipulation experiments with live beetles and pines demonstrate that the presence of conspecific beetles in the gallery environment strongly mediate fecundity, but D. frontalis is the only species which suffers negative impacts from the presence of heterospecific beetles in the gallery environment. Interactions between beetles did not result in any apparent fitness effects for the progeny of either species, which suggests that multispecies aggregations and co-colonization may be a dominant ecological strategy in the region.