Body size influences male pheromone signals but not the outcome of mating contests in Nasonia vitripennis

Adult body size may reflect the availability of nutrients during the development of insects and often covaries with mate quality parameters influencing the outcome of both inter- and intrasexual selection. But large males are not necessarily advantaged in contests for mating partners, because smaller competitors may compensate for lesser physical strength by an increased mating agility. In mating systems involving sexual signalling before mating, body size might be a crucial parameter given that the signal strength depends on the availability of limited nutritional resources. In the parasitic wasp Nasonia vitripennis, the male sex pheromone is produced from the polyunsaturated fatty acid linoleic acid. Here we tested the influence of body size on male sex pheromone titres and the outcome of male–male mating contests. We found that large males had significantly higher pheromone titres and released the sex attractant in higher amounts than small males. In an open arena bioassay, virgin females preferred pheromone doses adapted to the amounts released by large males. When directly competing for a female, however, large and small males had the same mating success. Hence, small N. vitripennis males, albeit equally successful in direct competition, are likely to be disadvantaged by being less attractive from a distance.