Reactions

Mosquito repellent

I’m in the process of reading through this week’s C&EN and was looking forward to the article “A Better Natural Mosquito Repellent’’ (Oct. 4, 2021, page 8). Since I work in a forestry organization, our field crews are exposed to mosquitoes and, more worrisome these days, ticks.

While my career vastly differs from what I researched during my PhD, working with insect attractants and such over the past decade has opened my eyes to how badly the cause-and-effect way of thinking adds blinders to peripheral vision, aka thinking outside the box. This is a great example: put out a citronella candle, see fewer mosquitoes. We accept the outcome, but are we missing steps with the mechanism? In the end, does this knowledge even matter? Perhaps yes, perhaps no.

Given that p-menthane-3,8-diol (PMD) can be made at elevated temperatures, who’s to say the citronella candles are not producing PMD as the flame burns wax and generates the activation energy to convert citronellal. There would be ambient moisture in the air, and the proton could come from a number of sources. I have not taken the time yet to peruse the literature to see if any publications are out there that link PMD with a burning citronella candle, but it should be an easy connection to make with real-time mass spectrometry such as selected ion flow tube.

I’ve always wondered about insect lures. Once we deploy them, they are at the mercy of the elements, and what we believe is the attractant could merely be an intermediate where a decomposition or rearrangement product is the true active compound, since the same could be happening with the insect that naturally produces these compounds. We know they work only because we catch specimens, but if we found out the attractant was a smaller degradation product, it would possibly save us time and effort at the bench level with fewer synthetic steps.

Gaetan LeClair
Fredericton, New Brunswick