Date Published: February 7, 2018
Publisher: Public Library of Science
Author(s): Irene Saavedra, Luisa Amo, Michel Renou.
Chemical cues play a fundamental role in mate attraction and mate choice. Lepidopteran females, such as the winter moth (Operophtera brumata), emit pheromones to attract males in the reproductive period. However, these chemical cues could also be eavesdropped by predators. To our knowledge, no studies have examined whether birds can detect pheromones of their prey. O. brumata adults are part of the winter diet of some insectivorous tit species, such as the great tit (Parus major) and blue tit (Cyanistes caeruleus). We performed a field experiment aimed to disentangle whether insectivorous birds can exploit the pheromones emitted by their prey for prey location. We placed artificial larvae and a dispenser on branches of Pyrenean oak trees (Quercus pyrenaica). In half of the trees we placed an O. brumata pheromone dispenser and in the other half we placed a control dispenser. We measured the predation rate of birds on artificial larvae. Our results show that more trees had larvae with signs of avian predation when they contained an O. brumata pheromone than when they contained a control dispenser. Furthermore, the proportion of artificial larvae with signs of avian predation was greater in trees that contained the pheromone than in control trees. Our results indicate that insectivorous birds can exploit the pheromones emitted by moth females to attract males, as a method of prey detection. These results highlight the potential use of insectivorous birds in the biological control of insect pests.
Chemical communication is probably the most ancient and widespread form of communication [1, 2] and plays an important role in sexual selection [3, 4]. The chemical compounds emitted by animals and used in mate attraction and mate choice are known as pheromones . In many cases, the chemical signals involved in mate choice may allow potential partners to evaluate an individual´s quality. Theoretical models have predicted that signals can only be evolutionarily stable if they are condition-dependent, or costly to the signaler, and if the cost is correlated with the signaler’s quality [5–7]. Therefore, individuals can not afford to cheat, i.e., to signal at too high a level , and conspecifics can rely on the information provided by these honest signals.
The number of trees that had at least one caterpillar with signs of avian predation differed between treatments (GLM: Z = 2.40, P = 0.02, Fig 2). Ten out of the 16 trees containing a pheromone dispenser had at least one avian predation event (i.e., at least one artificial caterpillar had signs of avian predation, Fig 1). In contrast, a predation event was observed in only 3 out of the 16 control trees. The proportion of larvae damaged by the birds differed between treatments (GLM: Z = -3.72, P = 0.0002; see Table A in S3 Supporting Information), being significantly higher in trees that contained a pheromone (Mean ± SE = 3.04% ± 1.48%) than in control trees (Mean ± SE = 0.71% ± 0.54%).
Our results show for the first time that insectivorous birds can exploit sex pheromones for prey location . A greater number of trees were visited by birds (i.e., they had at least one artificial caterpillar with signs of avian predation) when they contained an O. brumata pheromone dispenser compared to a control dispenser (Fig 2). Additionally, a greater proportion of artificial larvae were predated when the tree in which they were located contained an O. brumata pheromone dispenser than when it contained a control dispenser.