Lunar Rhythm of Emergence, differential Behaviour of the Sexes, and other Phenomena in the African Midge, Chironomus brevibucca (Kieff.)

Abstract

Larvae of the African midge, Chironomus brevibucca (Kieff.), are abundant in the littoral zone of Lake Bangweulu, Northern Rhodesia, where, at certain times of the year, imagines emerge in vast numbers shortly after the appearance of the full moon. Attracted by light, the imagines fly to houses and alight on the protective gauze screenings, which, at peak periods of emergence, become covered with a solid mass of midges. They have not been seen at other phases of the lunar cycle, so the adult life is certainly not more than ten days and is usually much less.Imagines, which are inactive by day, tend to settle in different situations according to their sex. On the gauze screenings there was a marked preponderance of females (4·68:1) on the day following a night's swarming but, on several adjoining whitewashed walls, males predominated (2·92:1). On grasses near the lake margin females outnumbered the males.When, the gauze screening of a house was diffusely illuminated, imagines were attracted to it during the early hours of darkness. The first flies to arrive were almost invariably males, but females followed on rapidly and finally constituted the bulk of the population. On one evening the percentage of males fell in three hours from 95·4 at 1844 hr. to 29·5 at 2145 hr. The percentage of males reaches a minimum between 1900 and 2000 hr. and thereafter shows some rise, probably due to a secondary influx of males which are thought to have been resting during the day and not to be newly emerged.An indication of the adult age of males seems to be given by the condition of the antennae during the early part of their adult life.Some miscellaneous observations on the behaviour of C. brevibucca are recorded.Some aspects of the phenomena recorded are discussed. The recent hypothesis of Korringa, which seeks to explain the periodíc swarming of certain polychaetes just after the time of full moon as being the result of an additive effect of exposure to nocturnal illumination on the maturation of organisms that are not subjected to sunlight by day, is examined and shown to be applicable to C. brevibucca.