DEET as a feeding deterrent
The insect repellent N,N-diethyl-3-methylbenzamide (DEET), is a multimodal compound that acts as a spatial repellent as well as an irritant (contact repellent), thus being perceived by the insects olfactory and gustatory systems as an odorant and a tastant, respectively. Soon after DEET was developed, almost 6 decades ago, it was reported that it reduced mosquito feeding on blood mixed with this repellent. It is now known that the mosquito proboscis senses contact repellents with the tips (labella) of the labium, which remain in direct contact with the outer layers of the skin, while the stylets, including the feeding deterrent sensor (labrum), penetrate the skin. We designed a behavioral assay that allowed us to tease apart contact repellency from feeding deterrence. First, we demonstrate here that when DEET was mixed with blood and covered by Parafilm(R) layers, it did not leak to the outer surface. In our assays, the mean number of landings and duration of contacts with surfaces covering blood mixed with DEET or blood plus solvent (dimethyl sulfoxide) did not differ significantly. The feeding times, however, were significantly different. When blood was mixed either with 0.1 or 1% DEET, female southern house mosquitoes spent significantly less time feeding than the time spent feeding on blood mixed only with the solvent. By contrast, there were no significant differences in the mean times of feeding on blood containing 1% picaridin and blood plus solvent. Like DEET, the contact repellent and insecticide, permethrin, caused a significant reduction in feeding time. We, therefore, concluded, that in this context, DEET and permethrin act as feeding deterrents.