Age-dependent chemical signalling and its consequences for mate attraction in the gumleaf skeletonizer moth, Uraba lugens

Abstract

Theoretical models predict that virgin females at risk of not mating should strategically adjust their signalling investment as they age, with older, virgin females investing more to attract males. We explored how adult age influences the ‘calling’ (pheromone-releasing) behaviour of virgin female gumleaf skeletonizer moths, Uraba lugens, over four consecutive 10 h scotophases (dark periods). Adult virgin females commenced calling shortly after the onset of the scotophase. We found that female investment in calling behaviour changed with age: but in contrast with theoretical predictions and empirical observations in other species, older females were less likely to call and spent less time calling than younger females. Older females, however, commenced calling earlier in the scotophase, suggesting that there may be selection on older females to avoid competition from younger conspecific females. We also examined male olfactory preferences for pheromones from females of different ages. Y-maze assays showed that males preferred the pheromones produced by younger females, and that pheromone quality probably plays a role in this choice. Combined, these results suggest that female U. lugens may adaptively adjust their calling behaviour with age to mitigate against the risk of mating failure through competition with other females. The preference of males for pheromones produced by younger females is consistent with this interpretation.