Efficient traps for xenomonitoring onchocerciasis vectors: optimising visual cues for host seeking Simulium damnosum.

Lasane Koala

Background: Despite decades of research and a recognisable need, few traps have been developed and deployed successfully to sample or control disease vectors. The vectors of onchocerciasis in Africa, Simulium damnosum feed on human hosts by day at high biting and infection rates but there is no standard trap either for surveillance or control and human landing collection (HLC) remains the standard sampling method despite the ethical issues. We sought to develop replacement attractant traps for hostseeking S. damnosum, beginning with an investigation into visual and olfactory cues.

Method: Working in SW Burkina Faso, blackflies were caught with electrocuting grids at targets of different sizes, shapes, with synthetic odour baits. Numbers of blackflies/ trap or trap surface area/ day and total S. damnosum/ target area were compared in Latin square design tests.

Results: Larger square traps (<1 sq metre) caught more S. damnosum but the numbers caught per unit area declined with target size. Horizontal oblongs caught nearly 1.5 times more than square ones, and 3 times more than the vertical oblong. Shape preference was consistent over the range of target sizes. Blue targets collected more S. damnosum than black and blue-black targets. Experiments are ongoing.

Conclusion: These preliminary results from our studies on visual cues indicate that a trap for the savannah forms of S. damnosum could be horizontal oblong in shape and relatively small in size, measuring 0.25x0.25 m (0.0625m2). However, the next stage of the study, the evaluation the visual traps with added synthetic host odour blends, is underway at present and results will be presented at PAMCA.