Developmental instars of four species of mosquitoes have been analyzed for growth and synthesis of biomass with respect to their caloric content of
protein,
lipids, and
carbohydrates for each instar of Aedes aegypti and Culex pipiens of the subfamily Culicinae, and Anopheles albimanus, and An. gambiae of the subfamily Anophelinae. The diameter of the thorax grows during the intermolt, reflecting continuous increase in biomass because it correlates significantly with the larval synthesis of total
protein,
lipids, and
carbohydrates. For Ae. aegypti the fourth instar was sexed to disclose the sex-specific synthetic potential. In Ae. aegypti the
protein increased in linear proportion with larval body size, whereas
lipid synthesis followed a significant, exponential regression, which was clearly steeper in male larvae and most pronounced in the last instar. When normalized for size, the size-specific
protein and
lipid contents showed minimal levels of 0.25 and 0.1, respectively, regardless of standard or crowded rearing conditions. The rate of
lipid synthesis in Ae. aegypti was determined by incubating fourth instar larvae with (14)C-acetate and estimating the
lipids. The rate was highest in the early larvae and decreased towards the end shortly before pupation; in male larvae incorporation was twice the rate of female larvae. Cx. pipiens reached the largest body sizes of all species tested, with
protein and
lipids increasing linearly with size. Their minimal levels of size-specific caloric contents were around 0.35 for
protein and 0.25 for
lipids. Anopheles also showed a linear relationship between larval size and caloric
protein and
lipid contents. Their minimal threshold levels in size-specific contents were 0.35 for
protein and 0.2 for total
lipids, similar to Culex, but slightly higher than in Aedes.
Starvation of Ae. aegypti larvae and subsequent feeding partially improved their
lipid contents, but never to the levels of non-starving, optimal controls. Conversely, well-fed final instars exposed to complete
starvation showed a tremendous reduction of the
protein and
lipids contents in the surviving imagines, accompanied by 73% mortality. These results demonstrate the biosynthetic plasticity and the significance of the phagoperiod in Ae. aegypti during the final fourth instar for growth. The characteristic differences between these two subfamilies in their larval physiology are discussed in relation to ecological factors as encountered in the field under natural conditions, and in relation to our earlier findings on the reproductive physiology.