Larval crowding in Culex pipiens generates cumulative cascading effects under changing environmental conditions

Abstract

Density-dependent population regulation is a fundamental driver in the population dynamics of living systems, ensuring a balanced and sustainable maintenance in nature. It has been suggested that the adverse developmental and morphological effect of high larval density in container mosquitoes represents a significant limiting factor for population density, and the need to investigate this possible importance within the framework of field-based principles has been emphasized. This semi-field study, conducted under the natural thermal regime and using a natural population in Turkish Thrace, aimed to examine the effects of non-food-limiting larval density (crowding effect) in the mosquito species, Culex pipiens ( Cx. pipiens pipiens ). Trials were carried out consecutively between June and September 2022, and a total of 21,844 first-instar larvae were reared in 301 glass containers at seven larval densities, ranging from 0.03 to 2.00 mL⁻¹ of water. Survival rate and development time in larvae, along with sex ratio and wing length in emerging adults, were determined as indicative criteria of the crowding effect. The analysis performed on the 11,961 emerging adults revealed that increasing larval density in containers causes a decrease in survival rate, prolongs development time, and reduces wing length. Furthermore, the effect was found to be closely related to the thermal regime of the environment, being aggravated by repeated use of rearing water by the larvae and exhibiting a sex-specific pattern. The overall evaluation of the results suggests that larval crowding in Cx. pipiens acts as a significant driver of population dynamics in nature, and climate change may exacerbate this effect, making it increasingly severe over time.