Research Article: Optimizing Odor-Baited Trap Methods for Collecting Mosquitoes during the Malaria Season in The Gambia

Date Published: December 4, 2009

Publisher: Public Library of Science

Author(s): Musa Jawara, Renate C. Smallegange, David Jeffries, Davis C. Nwakanma, Taiwo Samson Awolola, Bart G. J. Knols, Willem Takken, David J. Conway, Georges Snounou.

Abstract: Baited traps are potential tools for removal or surveillance of disease vectors. To optimize the use of counter-flow traps baited with human odor (nylon socks that had been worn for a single day) to capture wild mosquitoes in the Gambia, investigations were conducted at a field experimental site.

Partial Text: Host odours play a major role in attracting blood-seeking nocturnal female mosquitoes [1]. The major African malaria vectors of the Anopheles (An.) gambiae complex are anthropophilic, with human sweat and skin residues being highly attractive [2], [3], and several candidate chemical component attractants have been identified [4]–[8]. Such knowledge may help develop mosquito traps that can reduce the contacts between vectors and humans, or as a surveillance tool. Initial studies have shown that MM-X ® counter-flow traps are useful to test the attractiveness of natural human skin emanations and synthetic compounds and the repellent effect of plant materials, under enclosed semi-field and open field conditions [9]–[11]. Traps baited with a nylon sock worn by a human subject for 12 hours or more can attract considerable numbers of anopheline mosquitoes under enclosed semi-field conditions [9], [11].

This study shows that MM-X counter-flow traps baited with human odour are effective in catching high numbers of wild An. gambiae s.l. females that transmit malaria locally as well as Culex and Mansonia nuisance mosquitoes. The release of CO2 had a major effect in increasing numbers of the mosquitoes caught in the baited MM-X traps, consistent with previous field studies indicating that CO2 enhances odour-baited catches [10], [17], [18]. An important finding of this study was that the presence or absence of a sleeper and the position of the trap (outdoor or indoor) did not significantly affect the catch numbers. This indicates that the traps baited with human odour and CO2 are robustly attractive even when placed outdoors, and can be used to sample mosquitoes without major confounding from people sleeping nearby. Traps immediately outside the huts caught more An. gambiae s.l. females at heights of 15 cm (near ankle height) or 150 cm (adjacent to the eaves) than at intermediate heights, and further testing showed that traps set at 15 cm from the ground had higher catches than traps set at 150 cm at any distance from the huts. For studies on relative attractiveness of different synthetic compounds to mosquitoes, it can be recommended to use traps outdoors at 15 cm height, in close vicinity to huts or houses.



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