Some Laboratory Observations on the Biology of Aedes (Stegomyia) Africanus
Investigations are reported on oviposition habits, development, and emergence patterns of the pre-adult stages of Aedes (Stegomyia) africanus (Theo.) under laboratory conditions. It was observed that water or at least a wet surface is necessary for oviposition and that the intensity of egg-laying takes place within 2 cm from water surface and is greater in those containers with deeper water levels. Post-oviposition embryonic development lasts an average of 6 days thus conforming with earlier findings (Gillett, 1955). The quantity of water does not affect either the period of post-oviposition embryonic development or the rate of egg hatching. However, an average of 75% of the eggs hatch within the first 13 days after flooding, leaving the rest to hatch in subsequent instalments. At 27°C, the second-instar larvae take the shortest time to develop while the fourth-instar larvae take the longest period. Generally, intra-instar variability in growth rates were observed except in the pupal stage. Emergence of the various pre-imaginal stages and pupation did not appear to have any regular periodicity. Of particular interest was the observation that the number of instars in this species varied from the normal number of four, a finding which is believed not to have been recorded previously in the family Culicidae.
Key WordsMosquito Aedes (Stegomyia) africanus oviposition embryonic development larval instars flooding periodicity life history
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