Integration of visual and olfactory cues of hosts and non‐hosts by three bark beetles (Coleoptera: Scolytidae)

Abstract

Abstract 1. There has been a long‐standing pre‐occupation with how phytophagous insects use olfactory cues to discriminate hosts from non‐hosts. Foragers, however, should use whatever cues are accurate and easily assessed, including visual cues.2. It was hypothesised that three bark beetles, the mountain pine beetle (MPB), Dendroctonus ponderosae Hopkins, the Douglas‐fir beetle (DFB), D. pseudotsugae Hopkins, and the western balsam bark beetle (WBBB), Dryocoetes confusus Swaine, integrate visual and olfactory information to avoid non‐host angiosperms (e.g. paper birch, trembling aspen), that differ in visual and semiochemical profile from their respective host conifers (lodgepole pine, Douglas‐fir, interior fir), and tested this hypothesis in a series of field trapping experiments.3. All three species avoided attractant‐baited, white (non‐host simulating) multiple‐funnel traps, and preferred attractant‐baited black (host‐simulating) traps. In experiments combining white, non‐host traps with non‐host angiosperm volatiles, bark beetles were repelled by these stimuli in an additive or redundant manner, confirming that these species could integrate visual and olfactory information to avoid non‐host angiosperms while flying.4. When antiaggregation pheromones were released from white traps, the DFB and MPB were repelled in an additive‐redundant manner, suggesting that beetles can integrate diverse and potentially anomalous stimuli.5. The MPB demonstrated the most consistent visual preferences, suggesting that it may be more of a ‘visual specialist’ than the DFB or WBBB, for which visual responses may be more contingent on olfactory inputs.