Mosquito Attraction: Crucial Role of Carbon Dioxide in Formulation of a Five-Component Blend of Human-Derived Volatiles

Behavioral responses of the malaria mosquito Anopheles coluzzii (An. gambiae sensu stricto molecular ‘M form’) to an expanded blend of human-derived volatiles were assessed in a dual-port olfactometer. A previously documented attractive three-component blend consisting of NH(3), (S)-lactic acid, and tetradecanoic acid served as the basis for expansion. Adding 4.5 % CO(2) to the basic blend significantly enhanced its attractiveness. Expansion of the blend with four human-derived C4-volatiles was then assessed, both with and without CO(2). Only when CO(2) was offered simultaneously, did addition of a specific concentration of 3-methyl-1-butanol or 3-methyl-butanoic acid significantly enhance attraction. The functional group at the terminal C of the 3-methyl-substituted C4 compounds influenced behavioral effectiveness. In the absence of CO(2), addition of three concentrations of butan-1-amine caused inhibition when added to the basic blend. In contrast, when CO(2) was added, butan-1-amine added to the basic blend strongly enhanced attraction at all five concentrations tested, the lowest being 100,000 times diluted. The reversal of inhibition to attraction by adding CO(2) is unique in the class Insecta. We subsequently augmented the three-component basic blend by adding both butan-1-amine and 3-methyl-1-butanol and optimizing their concentrations in the presence of CO(2) in order to significantly enhance the attractiveness to An. coluzzii compared to the three- and four-component blends. This novel blend holds potential to enhance malaria vector control based on behavioral disruption.