Evaluation of two counterflow traps for testing behaviour-mediating compounds for the malaria vector Anopheles gambiae s.s. under semi-field conditions in Tanzania

Female An. gambiae s.s. were released in an experimental flight arena that was placed in a semi-field system and left overnight. Catch rates for the MM-X and BGS traps were recorded. Data were analysed by fitting a generalized linear model to the (n+1) transformed catches.Both types of traps successfully captured mosquitoes with all odour cues used. When the BGS trap was tested against the MM-X trap in a choice assay with foot odour as bait, the BGS trap caught about three times as many mosquitoes as the MM-X trap (P = 0.002). Adding CO2 (500 ml/min) to foot odour increased the number of mosquitoes caught by 268% for the MM-X (P < 0.001) and 34% (P = 0.051) for the BGS trap, compared to foot odour alone. When lemongrass leaves were added to foot odour, mosquito catches were reduced by 39% (BGS, P < 0.001) and 38% (MM-X, P = 0.353), respectively.The BGS trap shows high potential for field trials due to its simple construction and high catch rate when baited with human foot odour only. However, for rapid screening of different baits in a contained semi-field system, the superior discriminatory power of the MM-X trap is advantageous.Due to the role of mosquitoes in disease transmission and their impact on human well-being through their biting behaviour, both commercial and scientific interest exists for efficient trapping devices. During the last century, a number of different mosquito traps and collection methods were developed (reviewed by [1] and [2]). Recently, variations of the CDC light trap [3], the OBET [4,5] and Mbita trap [6-8], electric nets [9] and different traps featuring counterflow geometry [10-14], have been used to evaluate the attractiveness of various complex host odours, individual volatile organic compounds, or mixtures thereof.While full body odour was often successfully used to attract mosquitoes [15-17], synthetic baits were developed to improve ease of use and to allow standardizing the attractant. As mosquito host-seeking behaviour is governe