Host plant odour and sex pheromone are integral to mate finding in codling moth

The great diversity of specialist plant-feeding insects suggests that host
plant shifts may initiate speciation, even without geographic barriers.
Pheromones and kairomones mediate sexual communication and host choice,
and the response to these behaviour-modifying chemicals is under sexual
and natural selection, respectively. The idea that the interaction of mate
signals and habitat cues facilitates reproductive isolation and ecological
speciation is well-established, while the traits and the underlying
sensory mechanisms remain unknown. The larva of codling moth feeds in the
apple. We show for the first time that the response of male moths to
female sex pheromone relies upon presence of a kairomone released from
apple. In a non-host tree, attraction to pheromone alone is very strongly
reduced, but is fully rescued by blending pheromone with the apple
kairomone. This affords a mechanism how host plant shifts shape new
mate-finding signals that can give rise to assortative mating and
reproductive isolation.