Sexy Mouth Odour? Male Oral Gland Pheromone in the Grain Beetle ParasitoidLariophagus distinguendus(Förster) (Hymenoptera: Pteromalidae)

Abstract

Throughout the animal kingdom, sexual pheromones are used for the attraction of mates and as courtship signals but also enable sexual isolation between species. In the parasitic waspLariophagus distinguendus, male courtship behaviour consisting of wing fanning, antennal stroking of the female antenna, and head nodding stimulates female receptivity leading to copulation. RecentlyL. distinguenduswas reported to consist of two different lineages, which are sexually isolated because males fail to elicit receptivity in foreign females. It is unclear, however, which part of the courtship behaviour triggers female receptivity and therefore could be a mechanism causing sexual isolation. Here we show that inL. distinguendusa nonvolatile male oral pheromone is essential to release the female receptivity signal. In contrast, male wing fanning and antennal contact play a minor role. Additionally, the composition of the oral pheromone depends on the developmental host and females learn the composition upon emergence from the host substrate. These results will enable more detailed work on oral sexual pheromones to answer the question of how they are involved in the speciation process ofL. distinguendusand other parasitoid species, for a better understanding of the huge biodiversity in this group.