Sound-Triggered Production of Antiaggregation Pheromone Limits Overcrowding of Dendroctonus valens Attacking Pine Trees

<span class="paragraphSection"><div class="boxTitle">Abstract</div>For insects that aggregate on host plants, both attraction and antiaggregation among conspecifics can be important mechanisms for overcoming host resistance and avoiding overcrowding, respectively. These mechanisms can involve multiple sensory modalities, such as sound and pheromones. We explored how acoustic and chemical signals are integrated by the bark beetle <span style="font-style:italic;">Dendroctonus valens</span> to limit aggregation in China. In its native North American range, this insect conducts nonlethal attacks on weakened trees at very low densities, but in its introduced zone in China, it uses mixtures of host tree compounds and the pheromone component frontalin to mass attack healthy trees. We found that <span style="font-style:italic;">exo</span>-brevicomin was produced by both female and male <span style="font-style:italic;">D. valens</span>, and that this pheromone functioned as an antiaggregating signal. Moreover, beetles feeding in pairs or in masses were more likely than were beetles feeding alone to produce <span style="font-style:italic;">exo</span>-brevicomin, suggesting a potential role of sound by neighboring beetles in stimulating <span style="font-style:italic;">exo</span>-brevicomin production. Sound playback showed that an agreement sound was produced by both sexes when exposed to the aggregation pheromone frontalin and attracts males, and an aggressive sound was produced only by males behaving territorially. These signals triggered the release of <span style="font-style:italic;">exo</span>-brevicomin by both females and males, indicating an interplay of chemical and sonic communication. This study demonstrates that the bark beetle <span style="font-style:italic;">D. valens</span> uses sounds to regulate the production of an antiaggregation pheromone, which may provide new approaches to pest management of this invasive species.</span>

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