Chemical interactions under the bark: bark-, ambrosia-, and wood-boring beetles and their microbial associates

The view of insects and their microbiota as a holobiont is increasingly relevant as globalization and climate change aids the spread of pests to new areas. Examples of such pests include bark, ambrosia, and woodborer beetles (BAWBBs hereafter) that are important natural components of forest ecosystem processes, but may also cause substantial damage in native and invasive ranges. Microbiota has been shown to perform various functions for these beetles, but we are only beginning to reveal the complex chemically mediated interactions among the beetle, the host tree and their microbiota. In this review we a) summarize current knowledge about the influence of beetle ecology in the formation of the holobiont, b) how microbial compounds may function as beetle semiochemicals, and/or contribute to nutrient acquisition, defence, and maintenance of the holobiont, c) the influence of external factors that affect the holobiont, and d) pinpoint open questions and suggest potential methods needing attention in order to utilize this knowledge in of management of invasive or outbreaking BAWBBs.