Pheromone Blend Does not Explain Old Male Mating Advantage in a Butterfly

In several insect species, male mating success is higher in older than in younger males, although condition diminishes dramatically with age. Two hypotheses are under debate to explain the counterintuitive pattern of old male mating advantage: first, an increased eagerness of older males to mate, driven by their low residual reproductive value, and second female preference for older males based on chemical cues such as sex pheromones (female choice hypothesis). In a series of experiments, we manipulated female olfaction, male pheromone blend and female age to test whether old male mating advantage prevails when the influence of male sex pheromones is controlled for, using the tropical butterfly Bicyclus anynana as model. We found that older males had a higher mating success than younger ones irrespective of female scent‐sensitivity and irrespective of male pheromone blend. Interestingly, older males were found to court more often and for longer time bouts than younger males. These results were independent of female age, although younger males courted younger females more often and for longer bouts than older females. Taken together, our results indicate that male courtship activity (1) is higher in older compared to younger males and (2) increases the mating success of older males. Olfaction and sensing pheromones, in contrast, were not a necessary prerequisite for old male mating advantage to occur and may use other cues than pheromones to assess male quality.