A whiff on the evening train announces that the person opposite you has sweaty feet. In a delicatessen, the same smell can be both wholesome and welcome—an indication that you are approaching the cheese counter. Bart Knols and Ruurd De Jong have another use for the reek that emanates alike from unwashed feet and delectable cheese. The Dutch entomologists think they can exploit it to trap mosquitoes and thus help to combat malaria.

Working at Wageningen Agricultural University, they have been investigating the chemical features of humans that attract vectors of malaria, especially Anopheles gambiae. Carbon dioxide in the breath is one powerful attractant. But there are …