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 NH3, (S)-lactic acid, and tetradecanoic acid served as the basis for expansion. Adding 4.5 % CO2 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 CO2. Only when CO2 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 CO2, addition of three concentrations of butan-1-amine caused inhibition when added to the basic blend. In contrast, when CO2 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 CO2 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 CO2 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.