Control of phlebotomine sand flies (Diptera: Psychodidae) by means of vertical fine-mesh barriers

The leishmaniases are diseases transmitted by phlebotomine sand flies. Leishmania parasites cause a variety of symptoms, from cutaneous ulcers to fatal visceral disease. Control of Phlebotomine sand flies is problematic because the breeding sites of their immature stages are mostly unknown and usually inaccessible. Larval source reduction, which is the main approach to mosquito control, is impractical in the case of phlebotomines. Therefore most strategies are aimed at interrupting contact between sand flies humans. In this study we utilized vertical fine-mesh insecticide-treated barriers to block sand flies from reaching their targets. The concept relied on the sand flies landing on the vertical barrier as they proceed upwards and thus absorbing lethal amounts of insecticide. Two mesh types were initially tested on a small scale using two fenced enclosures (10×10m, 2m high) in the Jordan Valley in Israel. We tested the pyrethroid pre-impregnated PermaNet® (Vestergaard-Fransden ApS., Denmark) mesh (225 holes/inch²) and the SpiderNet+® (Meteor Inc., Israel) mesh (2,500 holes/inch²). Both barrier types exhibited over 90% efficacy in blocking sand flies from entering the enclosures (P<0.01). The PermaNet® is lighter, less expensive and comes ready impregnated with delta-methrine, and was thus selected for a larger scale trial in an urban setting. Results demonstrated 82% reduction in the mean number of sand flies trapped along the barrier compared with the control area adjacent to it (P<0.05). Vertical fine-mesh barriers are effective in preventing sand flies from approaching inhabited areas, and can significantly reduce the sand fly burden and spread of leishmaniasis in endemic foci.