Studies on the flight patterns of foraging sand flies.

Phlebotomine sand flies transmit Leishmania parasites that cause leishmaniasis in humans. We report experimental results that improve our understanding of how foraging sand flies proceed over flat or sloping ground and how they negotiate vertical obstacles. Three rows of traps were suspended at different heights on a wire fence. Those just above ground level captured 87% of all flies, traps set at one meter captured 11% while only 2% of the flies were captured in traps set two meters above ground. When traps were deployed on a vertical support wall, the mean catch per trap was much higher than for traps suspended on the fence. Traps suspended just above ground level captured 57% of all flies, traps set at one meter above ground captured 27% of the flies and even traps set at two meters captured 16% of the flies. Although, most flies were still captured close to the ground, a higher percentage reached the second and third rows of traps. Sticky traps on a vertical wall produced similar results with significantly more flies alighting on the lower sections of the trap closest to the ground. On a vertical sand fly-proof net the overall dispersal of the flies was more like on a wall than in open space. Traps suspended just above ground level captured 49%, traps set at one meter above ground captured 36% and traps set at two meters captured 15% of the flies. Following spraying of the net with deltamethrin (1%), fewer sand flies were captured but the reduction was not statistically significant. Our conclusions are that being small and frail, sand flies tend to fly close to the ground probably in order to avoid being swept away by gusts of wind. When they encounter a vertical obstacle, they proceed upwards close to the obstacle with intermittent stops. Therefore, insecticide-sprayed walls or vertical nets should be effective for controlling sand flies approaching human habitation.