Sex-specific development causes patterned emergence in Culex mosquito

Abstract

In order to understand why adults of the Culex mosquito emerge in a manner that follows a well-defined mathematical pattern depending on the sex of the species, preliminary investigations were carried out to determine if sex-related differences exist in the rate of growth and development in the immature stages. Culex egg-rafts sampled from the natural breeding environment were hatched in the laboratory and a total of 583 first instar larvae were allowed to grow in isolation. The time taken for the isolated mosquitoes to molt into the next stage was recorded until the mosquitoes finally became adults. At the final molt, the sex of the mosquitoes was determined and assigned retrospectively to every molting stage. Of the entire isolated mosquito, 464 (220 males and 244 females) were able to reach maturity. We observed that the developmental process occurring in the immature mosquito is sex-specific between the fourth instar larva and pupa. This event gives male Culex approximately one-day advantage over females and explains why males always emerge first and dominate the first few days during the emergence period. The process also alters the pre-existing symmetry in the molting time distribution of the female mosquito. The outcome is a pattern that could be described as a logarithmic function of the emergence time in male Culex, and a power function of the emergence time in female Culex. We recommend an investigation of the other species of mosquito as well as other holometabolous insects to see if this observation can be reproduced.