The Cost of Growing Up Hungry: Sex-Dependent Effects of Larval Diet in Culex pipiens

Background: The environmental conditions in which holometabolous insect larvae develop influence many aspects of their life-history traits in adulthood. In the context of vector control programs, understanding how environmental factors affect larval development is essential. Taking the mosquito Culex pipiens as a model system, we experimentally manipulated the amount of larval food availability to determine ( i ) the food levels at which developmental stress becomes detectable and ( ii ) which phenotypic traits serve as reliable indicators of this stress. Larvae were reared under five nutritional treatments: 100%, 50%, 25%, 10%, and 5% of the ad libitum (ADL) condition. Results: Food restriction reduced survival, increased asynchronous development time, decreased female proportion, reduced wing size, altered wing shape, and increased variation in wing asymmetry. Most morphological responses were sex-dependent, with females showing greater sensitivity to nutritional restriction than males. Life-history and morphological traits showed a non-linear response, with thresholds detected around 33–38% ADL. Among the treatments tested, measurable developmental stress became apparent at 25% ADL, whereas severe population collapse occurred below 10% ADL. Developmental time and wing size were the most sensitive indicators of nutritional stress, while fluctuating asymmetry showed comparatively lower sensitivity. Conclusion: Overall, these findings provide a quantitative framework for defining biologically meaningful stress levels and optimizing mosquito rearing protocols used in vector biology studies.