Mechanism of host selection by tsetse flies

Mobility of tsetse flies is influenced by various factors including the search for a blood-meal. Field observations on the feeding behaviour of tsetse are difficult. The use of bait animals for experimental purposes may indicate food sources but not host selection under natural conditions. Availability and density of a particular potential host species in a tsetse habitat can influence the feeding habit of the latter. Flies are capable of adapting to new host species in the absence of the usual ones. Host selection might be due principally to availability of host(s) and not based on true preference. Tsetse flies respond to visual stimuli from moving objects. Their shape, colour and size are important factors eliciting visual response. Whether these factors are distinguished separately or in combinations is not clear. Odour emanating from live hosts causes up-wind olfactory response towards the source(s), resulting in actual landing on test targets even when the hosts are out of sight. The components of odour have not been isolated. It is therefore doubtful if host selection can be associated with odour, as this might imply that tsetse can differentiate the odours of the different potential hosts. The difficulties in ascertaining true host selection by tsetse are discussed to stimulate further investigations.