Symbiotic fungi and the mountain pine beetle: Beetle mycophagy and fungal interactions with parasitoids and microorganisms

Dendroctonus ponderosae, the mountain pine beetle, is consistently associated with two filamentous fungi, Grosmannia clavigera and Ophiostoma montium. Little is known about the prevalence of these fungi throughout beetle development and what interactions these fungi have with other organisms. The objectives of this study were to: (1) assess the prevalence of G. clavigera and O. montium throughout the development of D. ponderosae, (2) determine how G. clavigera and O. montium interact with other microbes isolated from tree phloem, and (3) determine the role of G. clavigera and O. montium in host habitat location by natural enemies. For objective 1, fungi were sampled from phloem adjacent to developing beetles. The incidence of filamentous fungi adjacent to brood increased as brood development progressed. Prevalence of G. clavigera and O. montium shifted over the developmental period of D. ponderosae. For objective 2, G. clavigera and O. montium were grown on agar alone and with microbes isolated from tree phloem to test if growth of G. clavigera or O. montium is impacted by other microbes. The relative yield (growth) of O. montium grown with microbes isolated from larval galleries was greater than the relative yield of O. montium grown alone. The relative yield of G. clavigera grown with these same microbes was less than or equal to the relative yield of G. clavigera grown alone. Bacillus pumilus , a bacterium isolated distant to larval galleries, inhibited growth of both G. clavigera and O. montium. For objective 3, attraction of natural enemies to tree bolts colonized by D. ponderosae hosts or inoculated with G. clavigera and/or O. montium was investigated. Sticky screen cylinders surrounding each log captured all landing insects. A positive relationship was observed between the capture of three parasitoid species and the number of D. ponderosae parent galleries. Natural enemy capture on fungus-inoculated bolts was never significantly different than control bolts; however, capture of two parasitoid species tended to be greater on bolts inoculated with both G. clavigera and O. montium than on all other treatments.