T he truck pulled over onto the shoulder of the dirt road and Marcia Castro, accompanied by a researcher and two technicians, walked up to a green house built on the shores of a small pond. Behind the building, the group set up what would be the first of a series of traps to catch mosquitoes in the rural region of Cruzeiro do Sul, in the state of Acre.
The chemical compound given off by the device has a smell that attracts mosquitoes of all sorts. On that late-July afternoon, the team was interested in the vessel for the parasite that causes malaria: Anopheles darlingi , an insect smaller than the common mosquito and Aedes aegypti, which can transmit dengue, the Zika virus, chikungunya, and yellow fever.
The house near the pond was ideal for capturing specimens, since the mosquito the researchers had in mind likes to lay its eggs in large bodies of still, shaded water.
The females normally bite from dusk to dawn, so the trap would be left on all night. While one technician set up the device, Marcia Castro chatted with the owner of the house. Castro asked if the boy had already had malaria. And dengue. Dengue was the worst. In the third house they visited that afternoon, the group was greeted by a woman and her teenage daughter, who looked ill.
At the first house, they found just two mosquitoes. The trap at the third house β where the sick girl lived β was full of Anopheles and mosquitoes of other species.
