Abstract
The mite and fungal biota associated with the mountain pine beetle (MPB) (Dendroctonus ponderosae Hopk.) may not be stable throughout an irruptive event. In congeneric beetles, variations in the frequency of their associated organisms affect population trends and similar effects may occur in MPB. We studied fungi and mite trends in a declining irruptive MPB population as it attacked three different pine hosts in the Colorado Front Range. During the study, we found two new associates including one biologically relevant mite and one beneficial blue-stain fungus. Fungi hyperphoretic on mites were also documented. This included beneficial and potentially detrimental species to the MPB. The frequency of several organisms varied between some years or pine hosts but not within male or female beetles. A large increase of Trichouropoda sp. and T. ips mites trended inversely with the declining beetle population, while a decrease in the beneficial blue-stain fungi trended similarly to the declining beetle population. We discuss the interactions and potential effects of phoretic biota in relation to (1) the MPB associates’ population trends, (2) the MPB incursions into cooler areas, and (3) the redundancy of blue-stain fungi carried by the MPB holobiont. These findings increase our knowledge of the mechanisms that influence MPB populations.
Highlights
In western North America, episodic irruptions of mountain pine beetle (MPB) (Dendroctonus ponderosae Hopk.) can severely affect large forested areas [1]
We documented five mite species phoretically carried by MPBs attacking P. contorta and P. ponderosa dominated stands and found the same species from a beetle attacked P. flexilis stand in 2013 (Table 1)
One of the most common mite species we found was an oribatid in fungus is the dominant species during thermally inversed conditions to those considered to be their the genus Trichouropoda, this mite has only recently been reported in association with the MPB [69,70]
Summary
In western North America, episodic irruptions of mountain pine beetle (MPB) (Dendroctonus ponderosae Hopk.) can severely affect large forested areas [1]. Mortality events caused by the MPB foster changes in tree age structure by removing old and unhealthy trees while creating space for young and vigorous trees of the same species to grow [2]. These events can alter ecological succession by facilitating the emergence of a different tree species composition on the landscape. Tree mortality is not solely caused by the beetle’s action and, as in other bark beetle species, several organisms use adult MPBs to gain transportation from one tree to the At any time, these organisms can affect the success of the beetle and the type of damage caused to trees
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