A larval aggregation pheromone as foraging cue for insectivorous birds

Although birds have traditionally been considered anosmic, increasing evidence indicates that olfaction plays an important role in the foraging behaviours of insectivorous birds. Recent studies have shown that birds can exploit herbivore-induced plant volatiles and sexual pheromones of adult insects to locate their prey. Many insectivorous birds prey on immature insects, providing relevant ecosystem services as pest regulators in natural and agricultural ecosystems. We asked whether birds could rely on chemical cues emitted by the immature stages of insects to prey on them. To address this question, we performed field experiments to evaluate if insectivorous birds can detect the aggregation pheromone produced by the larvae of the carpenter worm, Chilecomadia valdiviana. Groups of five artificial larvae were placed in branches of 72 adult trees in a remnant fragment of a sclerophyllous forest in central Chile. Each grouping of larvae contained a rubber septum loaded with either larval pheromone as treatment or solvent alone as control. We found that the number of larvae damaged by bird pecks was significantly higher in groups with dispensers containing the larval extract than in control groups. Our results show that birds can rely on immature insect-derived chemical cues used for larvae aggregation to prey on them.