Observations on Chironomidae at Khartoum

Abstract

This paper deals mainly with species ofTanytarsus(CHIRONOMIDAE) at Khartoum, particularly the very commonT. lewisiFreeman. These midges are a serious pest there, usually between November and April, causing great annoyance by swarming in vast numbers around lights during the first few hours after sunset and thus interfering with work and pleasure in the riverain area. They are probably responsible for a considerable amount of asthma and other conditions due to allergy. Little information is available about the biology of CHIEONOMIDAE in Africa, so reference is made to the PalaearcticT. mancusWalker, to whichT. lewisiis closely related. Studies of Chironomids from the health point of view elsewhere have little relation to the Khartoum problem, but work onChaoborus(CULICIDAE) is of interest.The conditions under which these midges occur at Khartoum and the methods of study are described.At least 26 species of CHIRONOMIDAE, including four ofTanytarsus, occur at Khartoum. The respiratory organs of some pupae are figured, and a key, based on the characters of these organs, is given for some of the species.Observations on the biology of all stages are recorded, particularly on the vertical movements and drifting of larvae and pupae and the time of emergence. Many larvae and pupae drift downstream at night, andT. lewisiemerges mainly in the early morning.Some exploratory field trials of larvicides were carried out. The results were inconclusive, and the difficulty of assessing them is pointed out. Thorough control by anti-larval measures would be extremely difficult owing to the large size of the river and the drift of pupae from upstream. It is believed that it might be possible but prohibitively expensive, and would have to be repeated annually, perhaps throughout the midge season. Various protective measures are discussed. It is considered that riverside dwellers who can do so should move inland, and that a barrier of trees parallel to the river would protect houses away from the river front. People who must be near the river in the evening can achieve considerable protection by clearing some vegetation, fogging with insecticide, or using air-cleaning or air-conditioning equipment.