Relative Attractiveness Of Anopheles Gambiae Mosquitoes To Synthetic Odour Blends And Human Emanations

ABSTRACT

Mosquito host seeking behaviour is mediated by chemical, physical and visual cues. Identification of chemical and physical cues utilized by mosquitoes in host location can lead to the development of novel vector management strategies. This research set out to identify synthetic odour blends that simulate human body emanations that can be used to develop mass trapping devices for vector management. The relative attractiveness of human body emanations and synthetic odour blends as attractants of Anopheles gambiae mosquitoes was investigated under semi-field conditions at the International Centre for Insect Physiology and Ecology (ICIPE) Mbita Point, western Kenya. The effect of heat and moisture on the response of An. gambiae to synthetic odours was also investigated. Binary choice tests were conducted by exposing mosquitoes to natural odours from a human volunteer occupying one tent and synthetic odour blends delivered through a Mosquito Magnet-X® trap positioned in a second tent. Two human male volunteers previously established as person less attractive (Person LA) and person highly attractive (Person HA) to host seeking female An. gambiae mosquitoes, were recruited into the study to serve as sources of natural host seeking cues. Mosquito responses to foot odours adsorbed onto the persons‟ worn socks were also evaluated. This acted as an alternative natural source for host seeking cues. Synthetic stimuli were derived from two odour blends, a standard blend consisting of carbon dioxide, ammonia and distilled water and Blend 1 consisting of seven carboxylic acids, lactic acid, carbon dioxide, ammonia and distilled water. One hundred female mosquitoes aged between 3 – 6 days old and starved for 8 hours were used in each binary assay. Experiments were conducted between 1930 – 2000 hours and 2030 – 2100 hours each night. Mosquitoes attracted to the odours from the two sources, human volunteers and synthetic stimuli or foot odours were counted and recorded for every replicate. Data analysis was carried out in the General Statistical analysis software (Genstat®). Using Generalized Linear Model the number of mosquitoes attracted to odour baits person‟s emanations, their foot odours or synthetic attractants were modelled as a proportion of the total number of mosquitoes recovered. The data was transformed to assume normal distribution using a logarithm link function. Person LA attracted a higher proportion of female mosquitoes when compared to the standard blend (P = 0.001). However, the proportion of mosquitoes attracted to person LA when compared to foot odours and Blend 1 did not differ (P = 0.417; P = 0.163, respectively). Person HA on the other hand attracted a significantly higher proportion of mosquitoes when compared to his foot odours, standard blend and Blend 1 (P = 0.001). Augmentation of synthetic blends with heat (25-27oC) did not increase attractiveness of these odours to mosquitoes. Both persons attracted a significantly higher proportion of mosquitoes when compared to their foot odours, standard blend and Blend 1 when these were augmented with moisture (75 – 85%) (P = 0.001). A significantly higher proportion of mosquitoes were attracted to person LA compared to the standard blend (P < 0.001) and his foot odours (P < 0.001) when each was augmented with both heat (24.9oC) and moisture (75%). There was no difference in the proportion of mosquitoes attracted to person LA when compared to blend 1 (P = 0.416) augmented with both heat (24.9oC) and moisture (75%). The findings of this study have demonstrated that heat and moisture had no effect on attraction of mosquitoes to synthetic odours. Synthetic blend 1 was the most potent mosquito attractant. This synthetic blend should be incorporated in traps to mediate mosquito host seeking behaviour that would enhance capture of mosquitoes in field studies