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An isolate of the entomopathogenic fungus Beauveria bassiana (Bals.) Vuill. (Deuteromycotina: Hyphomycetes) was tested for its ability to reduce survival and reproduction of spruce beetle, Dendroctonus rufipennis (Kirby) (Coleoptera: Scolytinae), under laboratory and field conditions. Conidial suspension applied directly to adults or to filter papers that adults contacted had a median survival time of 3-4 d in laboratory assays and beetles died more rapidly when exposed to conidial suspension than when treated with surfactant solution only. In the field, conidial suspension was applied to the surface of felled and pheromone-baited Engelmann spruce (Picea engelmannii) trees using a backpack sprayer. Mortality of colonizing parent beetles (F0), reproduction (abundance of F1 offspring in logs), and emergence of F1 beetles from logs was compared between treated and nontreated logs. Application of spore suspension increased mortality of F0 adults by 36% on average. Total F1 reproduction was reduced by 17% and emergence from logs was reduced by 13% in treated logs, but considerable variability in reproduction and emergence was observed. Viable spores were re-isolated from treated logs up to 90 d after application, indicating that spores are capable of long-term persistence on the tree bole microhabitat. Subsequent in vitro tests revealed that temperatures below 15°C and exposure to spruce monoterpenes likely limit performance of B. bassiana under field conditions, but exposure to low-intensity light or interactions with spruce beetle symbiotic fungi were not strongly inhibitory. It is concluded that matching environmental tolerances of biocontrol fungi to field conditions can likely improve their usefulness for control of spruce beetle in windthrown trees.

The mountain pine beetle, Dendroctonus ponderosae (Coleoptera: Scolytinae), is an economically important bark beetle species with a wide geographic range spanning from the southwestern United States into northern Canada. This beetle causes extensive tree mortality to 13 pine species. Mites (Acari) are common and abundant symbionts of mountain beetles that may influence their fitness through positive and negative interactions. We present a unique assessment of the mite associates of mountain pine beetles using measures of alpha and beta diversity. We sampled phoretic mites from five beetle populations: Arizona, Colorado, South Dakota, Utah (USA), and Alberta (Canada) that varied in host tree species, local climate, and beetle population level. We collected 4848 mites from 8 genera and 12 species. Fifty to seventy percent of beetles carried mites in flight with the highest mite loads occurring in middle and southern populations; decreasing in northern populations. Mite assemblages (i.e., both richness and composition) varied along a south to north latitudinal gradient and were driven by species turnover (i.e., species replacement). Differences in mite composition increased with distance between populations. We discuss climatic variation, environmental filtering, and host tree differences as factors that could affect differences in mite composition between beetle populations and discuss implications for functional shifts. Our results could represent a model for estimating diversity patterns of mite symbionts associated with other major insect pests in coniferous forest systems.

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