Seasonal Variation in Sex Ratio of Aedes triseriatus (Diptera: Culicidae) and Its Dependence on Egg Hatching Behavior 1

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Abstract
Newly hatched larvae of Aedes triseriatus (Say) collected from treeholes displayed a seasonally variable sex ratio. The initial spring hatches of overwintered eggs were predominantly males, and subsequent hatches produced progressively smaller proportions of male larvae until females were the dominant sex. Primary sex ratios of geographic strains of A. triseriatus or progeny of male-predominant spring broods were not distorted. Ovitrap studies showed that females deposited equal numbers of male and female eggs throughout the year. Exposure to a hatching stimulus in the laboratory resulted in more rapid response by male embryos than females. Overwintered eggs in treeholes hatch in installments because hatching stimuli and/or conditioning factors are suboptimal, and the more ready hatching of males generates the seasonally characteristic sex ratios. Male and female embryos also show slight differences in photoperiodic response which do not contribute to seasonal distortion of sex ratio.