Shasta County CA, monitors West Nile virus (WNV) prevalence in the mosquito population through mosquito traps that expel carbon dioxide. Mosquitoes are drawn to carbon dioxide – the same compound exhaled by the people and animals that mosquitoes feed upon.
As such, the district works through 300 pounds of dry ice in the traps every two weeks, reports biologist John Albright of the Shasta Mosquito and Vector Control District. Collecting between 300 to 500 at a time, the trapped mosquitoes are then gassed to unconsciousness and separated by species before being sent for laboratory testing.
Every year since its arrival in Shasta County in 2004, the West Nile Virus transmission rate has peaked during the months of July and August when the Culex spp. mosquitoes that spread the disease are at their peak populations, Albright previously said.