Canadian Forest Service Publications

Assessment of the impact of symbiont Ophiostomatales (Fungi) on mountain pine beetle (Coleoptera: Curculionidae) performance on a jack pine (Pinaceae) diet using a novel in vitro rearing method. 2015. Myrholm, C.L.; Langor, D.W. The Canadian Entomologist 148(1):68-82.

Year: 2015

Issued by: Northern Forestry Centre

Catalog ID: 36550

Language: English

Availability: PDF (request by e-mail)

Available from the Journal's Web site.
DOI: 10.4039/tce.2015.28

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A novel “rearing-tube” method was developed and used to investigate the performance of mountain pine beetle (MPB), Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae: Scolytinae), with its three main ophiostomatalean fungal symbionts, Grosmannia clavigera (Robinson-Jeffrey and Davidson) Zipfel, de Beer, and Wingfield (Ophiostomataceae), Ophiostoma montium (Rumbold) von Arx (Ophiostomataceae), and Leptographium longiclavatum Lee, Kim, and Breuil (Ophiostomataceae). Transparent glass tubes filled with sterile ground jack pine (Pinus banksiana Lambert; Pinaceae) phloem and sapwood (9:1 ratio) were used to rear MPB from egg to adult with each fungus under controlled environmental conditions. Mountain pine beetle mortality was higher and development longer in fungus-free controls compared to fungal treatments. Among fungal treatments, insects developed faster, constructed shorter larval galleries, and had fewer supernumerary instars with L. longiclavatum. Insect survival was not affected by fungal treatments. Hyphal extension through the rearing medium was fastest for L. longiclavatum. Phloem nitrogen was reduced significantly by the presence of L. longiclavatum. Results support the hypothesis that ophiostomatalean symbionts provide benefits to MPB. The rearing-tube method is useful to tease apart confounding interspecific interactions between bark beetles and symbiotic fungus species.

Plain Language Summary

The purpose of this research was to develop a new method of rearing mountain pine beetles from egg to adult in a way that allows us to perform experiments. The technique was used in an experiment that examined how three species of fungi affect the growth and survival of mountain pine beetles reared on jack pine phloem, the innermost layer of bark. The technique uses small-diameter transparent glass tubes filled with ground phloem and sterilized with heat. Individual fungi were added to the phloem, and a single mountain pine beetle egg was added to each tube. All fungi improved mountain pine beetle growth and survival compared with fungus-free controls. Of the three fungus species tested, Leptographium longiclavatum significantly aided development of mountain pine beetle compared with the two other fungi, but mountain pine beetle survival rates were similar with all three fungi. It is important to know that L. longiclavatum is the most advantageous fungus for mountain pine beetles on jack pine bark. In boreal forests where jack pine is found, L. longiclavatum is the fungus most commonly found with mountain pine beetle. In other parts of the beetle’s range, other fungi species are more common. This suggests that ecological interactions between mountain pine beetle and other species are different in the boreal region, which the beetle has recently invaded, compared with other parts of its range. If this is true, the large body of science about the mountain pine beetle in other forest ecosystems in western Canada and the United States may not be directly applicable to mountain pine beetle populations in the boreal region.