Phoretic mites associated with Dendroctonus beetles and their invertebrate predators Richard W. Hofstetter, Elisabeth Alden, John C. Moser 1, and Karen M. Clancy 2 Northern Arizona University, Flagstaff, AZ USDA Forest Service, Pineville LA 1 and Flagstaff AZ 2 Introduction Mites are common associates of bark beetles and are known to influence beetle reproduction and beetle-fungal relationships. Mites may also affect beetle survival by preying on beetle eggs and larvae. Many mite species introduce fungi into bark beetle galleries and surrounding phloem (e.g. Tarsonemus mites; Lombardero et al. 2003, Hofstetter et al. 2005). Mites travel from tree to tree on beetles but cause no direct harm to the adult beetle (termed “phoretic”). Objective To identify and quantity mites that travel on Dendroctonus beetles and their predators and competitors within Ponderosa pine forests of Arizona. Materials and Methods We collected live insects from baited funnel traps (see picture) from June to October 2005 to estimate the prevalence of mites on bark beetles and associated organisms in Arizona (USA). We baited traps with synthetic lures designed to attract Dendroctonus frontalis, D. mexicanus, D. brevicomis, D. pseudosugae, D. valens, D. approximates and D. adjunctus bark beetles. Acknowledgements: Support for this research was provided by USDA Forest Service and USDA Joint Venture Agreement. Thanks to Stacy Bloomquist for assistance with lab work. Results  Overall, we collected 1500 insects and identified 1700 mites from beetle exoskeletons.  Approximately 32 species of mite have been identified and one new species (undescribed) was found on the predator, Temnochila chloridia. Of the insects surveyed, D. valens, D. frontalis and D. mexicanus had the greatest diversity of mites.  All insect species had phoretic mites. Predators and woodborers tended to have the highest loads of mites, often greater than 150 per insect. Although many of the Dendroctonus species and predators in Arizona inhabit the same infested trees, some mite species were associated with only one or two beetle species.  20% of the mite species identified were found only on predators and competitors, and 34% were found only on Dendroctonus. Conclusions The degree to which mite species affect bark beetle populations is unclear, but their high relative abundances and diversity on bark beetles suggest that they may influence the dynamics within infested trees and affect beetle fitness. This research will continue to study the introduction and transfer of fungi by mites within beetle infested trees and determine the effect this has on beetle population dynamics. References: Lombardero et al Strong indirect interactions among Tarsonemus mites (Acarina: Tarsonemidae) and Dendroctonus frontalis. Oikos 102: Hofstetter et al Seasonal dynamics of mites and fungi and interactions with southern pine beetle. Environmental Entomology (in press) Hofstetter et al Antagonisms, mutualisms and commensalisms affect outbreak dynamics of the southern pine beetle. Oecologia (in press). Plots (near Flagstaff, AZ) Distribution of D. frontalis Tarsonemus spp. fungal spores Table 1. Phoretic mites on Dendroctonus species Table 2. Phoretic mites on Dendroctonus predators and competitors phoretic mites Funnel trap