Rearing temperature influences flavivirus vector competence of mosquitoes

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Abstract
Culex annulirostris Skuse mosquitoes (Brisbane strain) were reared at 20oC or 27°C and the adult females were experimentally infected by feeding Murray Valley encephalitis virus (MVE). They were then maintained (a) in the insectary at 20°C, after rearing at either 20°C or 27°C; (b) at ambient outdoor temperatures, range 12.2–28.9°C, mean 19.6°C; or (c) at 27°C after rearing at 27°C. There was no significant difference in rates of MVE infection or transmission when mosquitoes were reared and maintained constantly at 20°C or 27°C. However, for females kept at reduced temperature (i.e. x = 19.6°C or 20°C after rearing at 27°C), the infection and transmission rates of MVE were significantly reduced (2times8 replicates). This investigation illustrates that vector competence is depressed by decreasing temperatures for adult mosquitoes compared with those they experienced during development. Similar patterns were evident with previously published work on Japanese and St Louis encephalitis, dengue and yellow fever. The process appears to be reversible, i.e. increased temperature raises virus infection and transmission rates. It is concluded that, without incubation at warmer temperatures, flavivirus recovery from overwintering mosquitoes will be negatively biased.