Background: African malaria vectors bite predominantly indoors at night so sleeping under an Insecticide-Treated Net (ITN) can greatly reduce malaria risk. Behavioural adaptation by mosquitoes to increasing ITN coverage could allow vector mosquitoes to bite outside of peak sleeping hours and undermine efficacy of this key malaria prevention measure.

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The effects of temperature and larval density on survival of larvae, growth rate, age at pupation, and adult size (measured as wing length and dry weight) of laboratory‐reared Anopheles gambiae (Diptera: Culicidae) were studied. Larvae were reared at three temperatures (24, 27 and 30 °C) and three densities (0.5, 1 and 2 larvae/cm2). The effects of density and temperature strongly interacted to determine the mosquitoes' life‐history parameters. Survival was highest at the intermediate temperature of 27 °C. The differences between the temperatures increased with increasing density. At 30 °C survival decreased as density increased, but at 27 °C increasing density led to higher survival. Age at pupation increased as temperature decreased from 30 °C to 24 °C and as density decreased from 2 to 0.5 larvae/cm2. Adult size also increased as temperature decreased, but showed a negative correlation with density only at 27 °C. In contrast, at 24 °C and 30 °C a decrease in density led to a decrease in adult size. Growth rate showed a similar pattern. At 27 °C growth rate decreased as density increased, but at other temperatures the opposite trend was observed.

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The influence of adult body size on the pre-gravid state and fecundity was studied in Anopheles gambiae Giles females hand-caught inside houses and virgin females collected as pupae in Tanzania. Blood-fed mosquitoes were kept for 2-3 days before dissection and examination for insemination and ovarian condition. Those females which did not develop eggs were classified as pre-gravid. The number of mature eggs in those mosquitoes which became gravid was counted. Virgin females were fed and kept for egg maturation in the laboratory. Wing-length of females was measured as an index of mosquito size. The overall pre-gravid rate in the resting An.gambiae population was found to be 21% and, of these, 66% had been inseminated. In the virgin females the pre-gravid rate was 92.6%. The mean wing-length of wild females which became gravid was significantly larger than those which remained pre-gravid. There was a positive correlation between fecundity and wing-length. Smaller females tended to require two or three bloodmeals to facilitate completion of the first gonotrophic cycle. The critical size permitting oviposition from the first blood-meal was a wing-length of 3 mm.