Size and sex in early developmental stages in a frog-biting mosquito

Sexual size variation in adult holometabolous insects may arise from selective pressures impacting ontogenetic stages associated with diverse habitats and resource use. In addition, scaling relations of these sexually dimorphic traits play an important role in morphological diversification. In mosquitoes, given the sexual differences in feeding strategies, investigations of the ontogeny of sexually dimorphic traits are of particular interest to understanding their reproductive biology and implementing early sex-separating technologies for vector control. However, our current knowledge of the morphological scaling of body parts over development across sexes is centered around a few well-known species of anthropophilic mosquitoes. In general, there is a noticeable gap in our understanding of the developmental biology of mosquitoes with limited medical consequences. One such mosquito is Uranotaenia lowii (Diptera: Culicidae), a species of growing interest due to its unique host use of feeding exclusively on frogs by eavesdropping on their mating calls. This study takes a step forward toward filling this gap by investigating sexual size dimorphism during the ontogeny of Ur. lowii. We examined larval and pupal stages to focus on traits that allow sex identification to evaluate various sex-sorting techniques that provide a foundation for experimental manipulation. We found that sex identification in Ur. lowii is possible during both larval and pupal stages. In the fourth larval instar, thorax length, abdomen length, and total body length differ significantly between the sexes, showing allometric scaling. In the pupal stage, the allometry of the head and thorax to body size remains consistent, as these parts fuse into the cephalothorax. Successful sorting based on cephalothorax length enables highly accurate pupal sex identification. This research sheds light on the biology of Ur. lowii, an understudied mosquito species, and lays the foundation for future studies on the developmental and reproductive biology of frog-biting mosquitoes.