The Relation Between Rainfall and Mosquito Populations

de Kruijf, H.A.

Immature stages of mosquitoes are all aquatic and require water in the form of either large permanent pools and streams or temporary rain pools or even small collections of water in fallen leaves or flowers. As the seasons in the tropics are marked by fluctuation in rainfall, it is not surprising to find that populations of many mosquito species follow these seasons very closely. However, while most population studies of adult mosquitoes show a general relationship between density and rainfall, based on monthly figures (see Aitken et al., 1968; de Kruijf, 1972b), they do not explain the detailed fall and rise of populations as related to changes in water supply. In an earlier study (de Kruijf et al., 1973), catches of adult mosquitoes in Beiem, Brazil, were analyzed to determine the day-to-day effect of rainfall on mosquito capture. First, it appeared that maximum catch of rain pool breeding species was related to the total rainfall in the four weeks preceding a catch. Second, either the number of dry days in the same period or the pattern of dry and wet days influenced maximum densities, while swamp breeders did not show such relationships. When the catch of rain pool breeders should have reached a maximum number according to the amount of rainfall, but did not, the number of dry days in the same period appeared to be either too low or too high. In other species there was either not enough or too much alteration between dry and wet days. It appeared that the rainfall total in 14 days preceding the fortnight before the catch and the number of dry days in that period was most critical. These conditions could be related to the duration of the immature stages. The present paper presents similar data for Surinam.

The Relation Between Rainfall and Mosquito Populations

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