Sugar diet affects Culex pipiens early-life mortality, biochemical parameters, and immunocompetence

Mosquitoes obtain carbohydrates from plants, providing a fundamental source of energy for their metabolism. These nutrients influence mosquito immunocompetence and longevity, which has potential implications for the transmission of mosquito-borne pathogens. We experimentally evaluated how sugar concentration in the diet of Culex pipiens females affected their survival rate, body mass, body composition (i.e., protein, lipid, glucose, and glycogen), and immunocompetence (i.e., number of hemocytes). To do so, we reared field-captured larvae in the laboratory, and the emerged mosquito females were randomly assigned to different concentrations of sucrose offered ad libitum (mass/volume%: 0.5%, 1%, 2%, 4%, 8%, and 16%). These solutions were chosen to represent the range of concentrations used in lab experiments and to simulate low to medium sucrose availability similar to what mosquitoes might encounter in different plants. Mosquitoes were analyzed at three different ages, 7, 14, and 21 days postemergence (dpe). We observed that mosquitoes fed on the highest sucrose concentration (16%) had reduced survival at 21 dpe, but their dry body mass increased. Protein, lipid, glucose, and glycogen content increased significantly with mosquito dry body mass. Furthermore, the diets with higher sucrose concentrations increased the lipid and glucose content but decreased the quantity of glycogen. Mosquito age significantly affected lipid content, it increased in mosquitoes from 7 to 14 dpe, when it reached its maximum value, and decreased in 21 dpe mosquitoes. In addition, we found a significant effect of the interaction between age and sucrose concentration on the quantity of glycogen. Seven dpe mosquitoes fed with lower sucrose concentration diet (0.5%, 1%, and 2%) had more glycogen than older mosquitoes, but in mosquitoes fed with higher concentrations of sucrose, the significant effect of age disappeared. The total number of hemocytes and oenocytoids varied with sucrose concentration, being more abundant in mosquitoes fed with the 1% sucrose concentration. The changes caused by the sucrose concentration of the diet on their mortality rate until 21 dpe, body composition, and immunity may ultimately affect the vectorial capacity of mosquitoes. This study contributes to a better understanding of how nutrition may affect the immunity of vectors and the outcome of vector-pathogen interactions.