How do mosquitoes find their host?
How do they know who you are and where to bite you?
Many studies have been done to determine how blood feeding (hematophagous) insects find their hosts. The principal attractant is carbon dioxide, the gas we breathe out as a waste product of our respiration. Mosquitoes smell with their antennae and their sense of smell is extremely sensitive to carbon dioxide levels in the air. They orient their flight pattern upwind to follow air currents containing a filamentous plume of carbon dioxide emanating from a host. As they get closer, the odors of other compounds, especially lactic acid emitted from the skin surface, allow them to find and identify a host. Their vision enables them to see the host and thermosensors on their antennae and mouthparts enable them to find the capillaries from which they feed. They pierce the blood vessel and inject their saliva that contains an anticoagulant, a compound that prevents the host's blood from clotting in their mouthparts and gut. They have a pump in their head that literally sucks blood from the host and mosquitoes will feed until their abdomen is fully distended. The female will fly to a protected area nearby and rest one or two days to digest the blood and absorb the proteins necessary for egg development. When mosquitoes ingest a blood meal that brings them to a state of engorgement, they stop seeking a host until after they produce eggs. We do not know the reason for this but it seems logical because the purpose of feeding on the blood of a host is to supply the nutrients necessary for egg production. She may feed on more than one host to ingest enough blood to produce each batch of eggs. This mechanism helps in the transmission of disease causing organisms such as viruses and protozoans.
We know that mosquitoes have three sets of receptor cell types that are sensitive to carbon dioxide, lactic acid and temperature, respectively. We believe that all these receptors must be stimulated at the same time to evoke the blood feeding response. The repellent DEET inhibits the lactic acid receptor cells, confuses the mosquito and prevents the blood feeding response. In other words, the mosquito will not bite when you wear DEET because it cannot smell lactic acid and cannot identify you as a host. Most insect repellents work in the same way, no matter what the source, they confuse the olfactory receptors and the mosquito cannot smell you.
E-Mail Jeannine Dorothy, Maryland Department of Agriculture Mosquito Control