Female and male Sirex noctilio use age and size to select a mate

While male mate choice in insects is a widely accepted concept, there is still limited evidence showing that lek formation is compatible with the evolution of male mate choice. In the woodwasp Sirex noctilio, males form leks that are used by females to select a mate. However, males have been observed to ignore certain females, suggesting the presence of male mate choice despite the presence of a lek mating system. In this study we demonstrate that males only attempt to mate with certain females. To understand the criteria used by males and females to select a mate, we also tested the effect of age, size, and male to female size ratio on the number of mating attempts made by males and on female receptivity. We demonstrate that size and age play a role in both male and female mate choice. Our results suggest that males must reach sexual maturity after emergence and are neither receptive nor attractive to females during the first few days of their lives. We also show that older females become less attractive to males, suggesting that female S. noctilio switch to a strict host location phase sometime after emergence. Our results show that male and female size, and the ratio between them, play a role in mate choice. While larger males are more motivated to mate, their large size can physically prevent them from mating with small females. Small females are also more attractive and more receptive to males, consistent with the presence of convenience polyandry in S. noctilio.