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. Methods Larvae were reared under five nutritional treatment levels: 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 nonlinear response, with thresholds detected around 33–38% ADL. Among the treatment levels 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. Conclusions Overall, these findings provide a quantitative framework for defining biologically meaningful stress levels and optimizing mosquito rearing protocols used in vector biology studies.