The insect repellent DEET is effective against a variety of disease vectors. It is particularly valued for its action against mosquitoes and it is estimated that some 200 million people across the world now use products containing DEET to protect them against the discomfort of mosquito bites and against diseases (most notably malaria and dengue fever) transmitted by various mosquito species. Nevertheless, exactly how DEET works remains unclear, despite a number of studies seeking to address this question.

A study earlier this year (1), which was also the subject of a TropIKA.net blog, provided support for the notion that mosquitoes do not actually ’smell’ DEET but instead it masks the odour of lactic acid in human sweat, effectively making humans ‘disappear’ from the insect’s point of view.

A new study (2) seems to contradict this. Researchers in the US performed recordings functional olfactory receptor neurons (ORNs) on the antenna and maxillary palps of Culex quinquefasciatus and found an ORN that respondedd to DEET in a dose-dependent manner. From this, and other findings in their study, they conclude that: ‘Our research shows that mosquitoes smell DEET directly and avoid it.’

Clearly more research is needed and it is certainly a possibility that different mosquitoes respond to DEET in different ways.

It is all interesting stuff and, if better idea is obtained of how DEET works, then it could lead to the development of further insect repellents. However, the people who are most at risk of mosquito-borne infections are the very poor. They are unlikely to be able to afford regular supplies of such products for daily use.

References
1. Ditzen M, Pellegrino M, Vosshall LB (2008). Insect Odorant Receptors Are Molecular Targets of the Insect Repellent DEET. Science 319 (5869), 1471. DOI: 10.1126/science.1153121.
2. Syed Z, Leal WS (2008). Mosquitoes smell and avoid the insect repellent DEET. Proc Natl Acad Sci USA; 105(36):13195-6. [Full study freely accessible here.]