Body size, sexual receptivity and larval cannibalism in relation to protandry among Toxorhynchites mosquitoes

Males of Toxorhynchites rutilus and T. amboinensis emerge as adults significantly sooner than females, the difference between sexes more pronounced in the latter species. In contrast to other protandrous mosquitoes, male and female T. rutilus do not differ in mean body mass and T. amboinensis females are only slightly larger than males. Protandry in the context of size similarity of the sexes is maintained by significantly faster growth of males. Sexual maturity is attained in both sexes approximately one day after adult eclosion, which occurs primarily in the late afternoon. Predatory fourth instar T. rutilus that co-occurred in treeholes were far more similar in body mass than individuals of that same stage that occupied different treeholes. In surrogate treeholes set experimentally in nature, the rate of cannibalism was significantly higher among T. rutilus fourth instars that differed in body mass. We propose that the size similarity which minimizes larval cannibalism selects against sexual size dimorphism in adults of these species.