Energy metabolism during diapause in Culex pipiens mosquitoes

Diapause in overwintering adult female Culex pipiens mosquitoes plays an important role in the transmission of West Nile and other encephalitis-inducing flaviviruses. To investigate the dynamic metabolic processes that control Cx. pipiens diapause, we used radioactive tracer techniques with [14C]-glucose to investigate the metabolic fate and flux of glucose in adult mosquitoes reared under diapause (18 °C, short day) and non-diapause (27 °C, long day) conditions. We found that by 72 h post-14C-labeling of 1-day-old mosquitoes, the diapause-destined mosquitoes had converted 46% more 14C-labled glucose into 14C-labled lipid than mosquitoes reared under non-diapausing conditions. When 5-day-old mosquitoes were fed [14C]-glucose, and then switched to water only, the non-diapausing mosquitoes oxidized nearly three times more 14C-labled glycogen and lipid by day 7 than diapausing-mosquitoes. This increased energy expenditure in non-diapausing mosquitoes is most likely due to temperature- and light-dependent increases in the basal metabolic rate. Amongst the diapausing-mosquitoes we analyzed over a subsequent 7-week period, we found that the amount of 14C-labeled glycogen decreased steadily for the first month of diapause, whereas, 14C-labeled-lipid levels were not significantly decreased until after day 35 of diapause, indicating that flux through glycogenolysis is higher than lipolysis during the first month of diapause. Lastly, our analysis revealed that 38% of the initial 14C-labled lipid that was synthesized during the adult pre-diapause phase was still present following the first gonotrophic cycle. About 33% of this remaining 14C-labeled lipid was localized to the newly developed eggs, suggesting that lipid sparing processes during a minimal 7-week long diapause may enhance egg production.