THE DESIGN OF TARGET BARRIERS FOR TSETSE-FLIES, GLOSSINA SPP (DIPTERA, GLOSSINIDAE)

Two small-scale experiments were carried out to test the effectiveness of narrow target barriers against re-invasion by Glossina pallidipes Austen and G. m. morsitans Westwood. The barriers consisted of either one or two lines of targets, with the targets placed at distances of c . 16 m apart within the lines. At this spacing the targets are so clos e together that a fly could scarcely fail to see at least one target a s it crossed the barrier. Nonetheless, in both cases, flies penetrated the barriers with probability c. 10% as judged by catches in odour-ba ited traps on either side of the barrier. Narrow barriers, even at ver y high target density, are ineffective against tsetse invasion. This a ccords with previous theoretical predictions and mark-recapture studie s, and suggests that wider barriers are needed for the prevention of r e-invasion of cleared areas by tsetse.