Submitted to: Experimental Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2006
Publication Date: 7/1/2007
Citation: Xue, R., Ali, A., Barnard, D.R. 2007. Effects of in vivo exposure to deet on blood-feeding behavior and fecundity in anopheles quadrimaculatus (diptera: culicidae). Experimental Parasitology 116(3) 201-204. Interpretive Summary: An important facet of the protection of humans from mosquito attack and mosquito-transmitted disease agents is application of the repellent deet to the skin. In laboratory studies of repellent effectiveness, however, contact with deet by mosquitoes is characterized by highly variable responses and/or mortality in the mosquito test population. This fact can result in unreliable estimates of repellent protection time and the potential for increased risk of exposure to mosquito-borne disease agents by the repellent user. In this study, scientists from the ARS Medical, Agricultural, and Veterinary Entomology Center in Gainesville, FL and the University of Florida examined the effects of contact with deet on blood feeding behavior, reproduction, and survival in malaria-carrying mosquitoes. They found that deet caused high mortality in females and that it took longer for them to land and engorge with blood on deet-treated skin than it did on skin that had not been treated with deet. The results of the study suggest that the protection times indicated for deet in laboratory bioassays may be longer than occur in nature and that the accuracy of laboratory repellent bioassays could be improved by using female mosquitoes that have not been previously exposed to deet.
Technical Abstract: This study determined the effects of contact with deet on guinea pig skin on morbidity and mortality in female Anopheles quadrimaculatus Say. Exposure, in this manner, to 10% deet (in ethanol) for 5 min, resulted in 98% mortality in mosquitoes after 24 h. The median probing time (PT50) required by females, when exposed to 0.1%, 1.0%, and 10% deet, was significantly (P <0.0001) longer (12.5, 12.1 and 19.1 sec, respectively) than the 6.8 sec required by females to probe ethanol-treated skin (control). Similarly, mean blood feeding rates in populations of females exposed to 1.0% deet for <=5 min (14.4%) was 6 x lower (P <0.001) (85.5%) than in females exposed to ethanol-treated skin, whereas the mean engorgement time on skin treated with 1.0% deet (66.3 sec) was significantly shorter (P <0.0001) than for females feeding on the control guinea pigs (105.9 sec). The mean number of mature oöcytes per female (fecundity) in treatment (1.0% deet) and control mosquitoes was not significantly different (P <0.0001). The responses to deet observed in this study suggest that repeated exposure of female An. quadrimaculatus populations to this repellent, in laboratory bioassays, could result in confounding of toxicant and repellent effects and inaccurate estimates of deet repellency.