Life table characteristics of Anopheles arabiensis (Diptera: Culicidae) under simulated seasonal conditions.

Life tables provide a summary of mortality and reproductive schedules and can help explain why certain species proliferate in particular environments. Life table characteristics of Alopheles arabiensis, under a range of simulated seasonal temperature were determined. F1 progeny of field-collected material were observed at four fluctuating temperatures with means of 17.9, 23.2, 26.1, and 21.4 degrees C, representing winter, spring, summer and autumn temperature profiles. Gonotrophic cycles, egg hatchability rates, mean male and female lifespans, reproductive rate, the intrinsic rate of increase, and generation times were calculated. Immature development was fastest in summer (11 d) compared with winter (32 d), resulting in less robust adults. Mean female lifespans were greater than those of the males and also increased with decreasing temperatures. From the age-specific survivorship curve and the gonotrophic cycles, females were found to lay large numbers of eggs especially during spring and summser. Under simulated winter conditions mosquitoes did not oviposit in the laboratory. It was also determined that summer reared mosquitoes are capable of giving just one infected bite while autumn reared mosquitoes can give two infected bites, increasing their transmission potential. Thus life table data go some way toward explaining late season transmission of malaria in South Africa.