Models of Trap Seeking by Tsetse Flies: Anemotaxis, Klinokinesis and Edge Detection

Odour-baited traps and targets provide a powerful method for controlling tsetse flies and the trypanosome diseases of which they are the vectors. In this paper we present three models of the way in which tsetse flies might locate odour-baited traps or targets. The first model is one of anemotaxis in which tsetse use directional information in the wind to locate the source of an odour. Anemotaxis is likely to be useful when the wind is steady and the vegetation is open. The second model is one of klinokinesis in which there is no directional information available to the fly which is only able to detect the presence or absence of the odour. Klinokinesis might be used when the wind is very variable or the vegetation is closed. The third model is "edge detection" in which the flies are only able to detect the edge of odour plumes. This strategy might be useful if the odour is evenly dispersed. Anemotaxis is a very efficient way of locating the source of an odour even when the directional information in the wind is slight. Klinokinesis increases the probability of a fly locating the source of an odour but the best strategy is still not very efficient. Edge detection is very efficient but depends on the spatial distribution of the odour. rategies available within each model can be regarded as "careful navigation", "point-and-shoot" or "intensive searching". Which of these is used by the flies depends critically on the amount of time for which a tsetse can remain in flight, the rate at which the flies samples the wind direction (for anemotaxis) and the turning rate (for klinokinesis). More detailed experimental information is needed in order to assess the relative merits of the various strategies in field situations.