Mgo osquito has come a long way. For years, was the market leader DEET, which protects the pests successfully, but only for an hour or two. Recently, Icaridin has become available. This lasts up to eight hours and is just as effective. But both are slightly toxic to cells grown in culture and their toxicity (if any) to human users is an ongoing debate. So the search is on for something that is not toxic at all.
Francesca Dani from the University of Florence, Italy, thinks she may have the answer. As she and her colleagues describe in the Journal of Agricultural and Food Chemistrythey looked at a range of chemicals called aldehydes and ketones, and, with a bit of tweaking, produced something like a good, long-lasting, safe mosquito repellent.
Dr. Dani knew from the scientific literature that some aldehydes and ketones have insect repelling properties. Such chemicals, however, vaporise faster than DEET. But she also knew from her own work that molecules called cyclic hydroxyacetates, which form from certain aldehydes and ketones when exposed to alcohol, evaporate significantly less. Perhaps that, according to her, is the key to the answers.
Therefore, she and her colleagues scored cyclic hydroxylated acetates and tested their mosquito repelling qualities against those of DEET and Icaridin. The standard way to do this is to spray some on the back of a volunteer’s hand and ask him or her to put both hands into a mosquito cage. The unsprayed hand acts as a control, so it is possible to determine, by comparing the number of insects that land on each, how effective a certain chemical is in insects.
As expected, DEET a protective efficacy score of 95% (calculated by subtracting the number of mosquito probings on the treated arm from the number on the untreated one, dividing this by the number on the untreated one and then multiplying it by 100). Such protection was granted by 8.3 micrograms of the stuff being applied per square centimeter of skin, and it lasted for two hours. In the case of Icaridin, one-fifth of that dose produces an equivalent repulsion for eight hours.
To the researchers’ delight, two of their hydroxylated cyclic acetyls performed as well as Icaridin. And when they tested them on cell cultures they found that one, called 12a in the paper for simplicity, did not kill any of the cells exposed to it.
DEET and Icaridin had a good run. DEET in the 1940s, to help protect American soldiers from mosquito-borne diseases while on campaign. Icaridin, with its longer protection period, arrived in the 2000s. If 12a is successful, however, both lives may soon reach the end of their useful lives. ■