Using semiochemicals to predict biotic resistance and facilitation of invading phytophagous insects

<p>Invasive species are leading causes of biodiversity loss and economic damage. Allocating limited resources towards prevention and management of invasions requires risk assessments based on ecological knowledge for species of potential concern. Interactions of potentially invasive species with heterospecifics in a novel community will contribute to biotic resistance and facilitation experienced by the invader, and thus the likelihood of establishment. To experimentally predict heterospecific interactions, we conducted field experiments using synthetic aggregation-pheromone lures to measure the response of ecologically relevant species (possible predators, competitors, and facilitators) to the simulated presence of two potentially invasive spruce bark beetles, the North American <em>Dendroctonus rufipennis</em> (tested in Norway) and the European <em>Ips typographus</em> (tested in eastern Canada). The Canadian beetle community responded strongly to <em>I. typographus</em> lures, suggesting potential for considerable biotic resistance, whereas <em>D. rufipennis</em> lures prompted little response by the Norwegian beetle community. <em>D. rufipennis</em> was attracted to <em>I. typographus </em>lures, suggesting potential facilitation between these species through cooperative mass attack on trees. Our findings will inform invasive-species risk assessments for <em>I. typographus</em> and <em>D. rufipennis</em> and highlight useful methods for assessing interactions among other taxa that rely heavily on semiochemical communication.</p>