Pharma: August 2008 Archives


August 18, 2008

Previously, I had mentioned that DEET appeared to work by blocking mosquitos ability to detect food. A new study being reported in PNAS (Abstract. Full text behind paywall.) claims that mosquitos actually are repelled by DEET:
The insect repellent DEET is effective against a variety of medically important pests, but its mode of action still draws considerable debate. The widely accepted hypothesis that DEET interferes with the detection of lactic acid has been challenged by demonstrated DEET-induced repellency in the absence of lactic acid. The most recent hypothesis suggests that DEET masks or jams the olfactory system by attenuating electrophysiological responses to 1-octen-3-ol. Our research shows that mosquitoes smell DEET directly and avoid it. We performed single-unit recordings from all functional ORNs on the antenna and maxillary palps of Culex quinquefasciatus and found an ORN in a short trichoid sensillum responding to DEET in a dose-dependent manner. The same ORN responded with higher sensitivity to terpenoid compounds. SPME and GC analysis showed that odorants were trapped in conventional stimulus cartridges upon addition of a DEET-impregnated filter paper strip thus leading to the observed reduced electrophysiological responses, as reported elsewhere. With a new stimulus delivery method releasing equal amounts of 1-octen-3-ol alone or in combination with DEET we found no difference in neuronal responses. When applied to human skin, DEET altered the chemical profile of emanations by a "fixative" effect that may also contribute to repellency. However, the main mode of action is the direct detection of DEET as indicated by the evidence that mosquitoes are endowed with DEET-detecting ORNs and corroborated by behavioral bioassays. In a sugar-feeding assay, both female and male mosquitoes avoided DEET. In addition, mosquitoes responding only to physical stimuli avoided DEET.

In the Times article, the original researchers seem unconvinced:

Leslie B. Vosshall, a researcher at Rockefeller University who was involved in the earlier study, said that her team stood by its work, and that its findings were based on a variety of experiments. So for now, at least, there still appear to be some mysteries surrounding DEET.

As I understood the original work, DEET does have a repellent effect at high concentrations and looking at their (schematic) diagrams, it's not clear to me that the DEET filter paper would have indeed blocked the food, especially as they did controlled trials with solvent instead of DEET. This is relevant to my interests, but luckily I don't need to understand how DEET works in order to slather myself with smelly insect repellent, plastic dissoving goodness.