Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/1998
Publication Date: N/A
Interpretive Summary: Mosquito repellents applied to the skin are the first line of defense for military troops deployed to areas of the world in which malaria, dengue, and other mosquito-transmitted diseases are present. The development of new repellents by ARS scientists at the Center for Medical, Agricultural, and Veterinary Entomology in Gainesville, Florida is the number one research priority of the Armed Forces Pest Management Board of the Department of Defense. Unfortunately, the time required to synthesize, develop, and test new repellents is many years; moreover, it is dangerous to use human subjects to test repellents outdoors in areas where mosquito-borne diseases such as malaria or dengue are present. The study reported in this paper shows how some of the biological characteristics of mosquitoes can affect the length of time a repellent protects a human being from mosquito bite. The most important finding in the study is that mosquitoes that have already obtained a blood meal, and are able to transmit a disease to humans, are as susceptible to a repellent as mosquitoes that have not fed on blood and which cannot carry disease. This means that extra-ordinary personal protection measures, such as frequent re-application of a repellent to the skin, are unlikely to result in an increased time of protection from the bites of mosquitoes that may be carrying disease. It also underscores the need to continue the development of new repellents that can are effective for long periods against a variety of disease carrying mosquito species.
Technical Abstract: Laboratory repellent bioassays were used to assess differences in the Complete Protection Time (CPT) provided by deet (N,N-diethyl-3-methyl- benzamide against 5 day-old nulliparous and 10, 15 and, 20 day-old nulliparous and parous female Aedes aegypti, Anopheles albimanus, and Anopheles quadrimaculatus. Mean CPT was shortest against An. albimanus (1.6 h) and An. quadrimaculatus (1.5 h) and longest against Ae. aegypti (6.5 h) but was unaffected by mosquito age or parity. Mean percentage biting at repellent failure time was highest in An. albimanus (14.2 percent) followed by An. quadrimaculatus (7.0 percent) and Ae. aegypti (2.9 percent), was higher in parous females (10.8 percent) than in nulliparous females (5.9 percent), and was highest in 20 day-old parous An. albimanus. Interaction between mosquito species and parity and between parity and mosquito age resulted from an increase in percentage biting by parous females, compared with nulliparous females (for Ae. aegypti and An. albimanus), and a significant increase in the biting response, relative to parity state, in 20 day-old females compared with 10 and 15 day-old females.