Effects of ecological changes on the malaria vectors Anopheles funestus and the Anopheles gambiae complex of mosquitoes in Accra, Ghana.

Studies have been conducted on mosquito breeding, indoor resting density and some parasitological and vectorial indices in Accra since 1911. An. gambiae s.l. has adapted to breeding appreciably in water-filled domestic containers in recent times (viz. 21.14 +/- 4.4% of all breeding), compared with a low frequency of breeding in such domestic containers in the earlier years 1911-1930 (viz. 1.97 +/- 1.67% of all breeding). Its breeding has also increased (viz. 5.3% to 25.4% of all breeding) in the numerous polluted water habitats created as a result of urbanization. This more widespread breeding in Accra city gave rise to only reduced indoor-resting densities of An. gambiae s.l. Several factors may be responsible for these changes, including the possible replacement of An. gambiae s.s. by the more versatile An. arabiensis as the predominant species in Accra. The almost complete elimination of An. funestus and decrease in breeding intensity of An. gambiae s.l. over the years have contributed to diminishing malaria parasite rates between 1912 and 1964 and may also account for low incidence of W. bancrofti infection in Accra in recent times.