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Just a note

These maps demonstrate several of the problems of producing accurate isoplethic maps.
  1. Ideally sampling should have been carried out on a regular grid, rather than the highly clustered pattern of trap sites that was used. This would have avoided the need for hypothetical 'zero-catch' traps, to pin the edges of the distribution. If traps really had been positioned long term in those sites (as they were for some of the time) they would have caught very few, but not zero flies. However a regular grid was not logistically feasible, due to the difficulties of servicing traps amidst very difficult terrain, and the fact that the land-owners' overriding interest lay in reducing the number of tsetse in their woodlands - not in academic research!

  2. The interpolation method inevitably reduces the apparent importance of very localised patches of high density. Hence the very high numbers caught in the narrow wooded valley to the west (see bar diagram maps) are reduced in the isoplethic maps because they are surrounded by dry scrub, which are given a zero catch. This therefore underestimates the importance of this valley as a reinvasion route in November.

    (From unpublished research of Brightwell & Dransfield. The collaboration of Russell Kruska, Brian Williams and Onyango Okello is gratefully acknowledged in the production of these maps).