Moonlight and house-haunting Habits of female Anophelines in West Africa

Abstract

1. 97 per cent, of the ♀ A. gambiae, A. funestus and A. melas remained until after dawn in the huts in which they had fed.2. ♀ A. melas seldom left suitable huts in the daytime.3. There was a high positive correlation between the time at which ♀ A. funestus entered huts and the time of moonlight. The maximum correlation coefficient was between the size of the catch at 8 p.m. and the duration of moonlight after this period, and its value was –0·783±0·068.4. During moonless periods, the flighting of ♀ A. funestus was partially inhibited, and when the moon came out, the waiting mosquitos entered the huts in greatest numbers. The average proportion caught when the moon rose during catching periods ending 10 p.m., midnight and 7 a.m. was approximately 50 per cent., 100 per cent. and 400 per cent. greater, respectively, than the proportion caught during these periods on moonless nights. On moonless nights many mosquitos waited until twilight of the following evening before entering the huts, and in consequence the average proportion caught in the period ending 8 p.m. was six times greater on moonless nights than on the nights after full moon.5. The records for ♀ A. melas are less complete, and the correlation coefficient for the relation between time of entry and time of moonlight has the value 0·421±0·184, a result which is barely significant. In view of the highly significant correlations found in the case of A. funestus it is unlikely that this correlation is fortuitous.6. The average rate of entry of ♀ A. funestus throughout one complete lunar cycle at Krabonekrom, Gold Coast, was 27 per cent. before 8 p.m., 22 between 8 p.m. and 10 p.m., 21 between 10 p.m. and midnight and 30 after midnight. The similar rates for A. gambiae (based on very few records), were 10, 20, 30 and 40 per cent. respectively. Comparable rates for A. melas in Sierra Leone are not available, but at least 45 per cent. entered before 10 p.m. (= 11 p.m. Gold Coast time).7. The essential difference between the behaviour of ♀ A. funestus and that of A. gambiae is that the former flight earlier than the latter. A. funestus also seem to be more active at dawn, so that they are more crepuscular in their habits than A. gambiae.8. 58 per cent, of the Anophelines caught at 8 p.m. were unfed. This indicates that early entrants usually rest after entry and before feeding, and average time of biting is later than average time of entry. Gravid or half-gravid mosquitos and those containing partly-digested blood, did not enter the huts; there was evidence that Anophelines usually became fully gorged at one feed. Of the Anophelines caught in huts after dawn 95 per cent, were fully fed.