Invertebrate and microbial associates
Coincident with and immediately subsequent to bark penetration, colonization and establishment of bark beetle and pathogen populations in the host, a myriad of associated organisms that are intimately associated with the bark beetles arrives at and finds access to the subcortical environment of infested trees. Although many of these associated species have been identified and cataloged, relatively little is known about the biology or impact of most species. Evaluation of the effects of associated species is difficult for a variety of reasons, including the wide expanse of taxonomic categories (ranging from pathogenic bacteria to arthropod parasitoids to avian vertebrate predators) and ecological groupings that encompass all aspects of multiple species interactions. In addition, the cryptic habit of these organisms within their hosts confounds efforts to sample and even to observe. As a result of these research difficulties, the importance of associates in promotion or natural control of bark beetles and pathogens may be underestimated. The perception that associated species have little effect cannot be supported or rejected unless research in this area is encouraged.