Submitted to: Medical and Veterinary Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/1997
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 and the costs for toxicological testing of these chemicals is millions of dollars. Both of these factors make it imperative that only the best candidate repellents be recommended for continued study and that such compounds be identified early in the candidate repellents evaluation process. The study reported in this paper shows how the testing conditions (cage size, mosquito density) currently used for this purpose can cause over-estimation of repellent protection times against mosquitoes. As a result, the authors recommend new and stringent repellent testing criteria that can be used to make the initial evaluation of repellent effectiveness. The new criteria should result in fast and conclusive determinations of repellent efficacy and will facilitate the identification and timely development of new and effective mosquito repellents for military use.
Technical Abstract: Mosquito biting rates and the mean duration (hours) of protection from bites (MDPB) of Aedes aegypti L. and Anopheles quadrimaculatus Say, using the repellent deet (N,N-diethyl-3-methylbenzamide), were observed in the laboratory in small (30 x 30 x 30 cm), medium (46 x 38 x 37 cm), and large cages (50 x 50 x 50 cm) containing low, medium, and high densities of mosquitoes (respectively, 640, 128, or 49 cm3 of cage volume per female). The MDPB for deet against Ae. aegypti ranged from 4.5 to 6.5 h and was significantly shorter (5.0 +/- 0.8 h) in large cages compared with medium (6.2 +/- 0.9 h) and small cages ( 6.2 +/- 0.8 h). In An. quadrimaculatus, the MDPB for deet ranged from 1.5 to 8.0 h, was shortest in small (3.7 +/- 2.3 h) and large cages (2.2 +/- 1.1 h) at medium (3.7 +/- 2.3 h) and high mosquito densities (2.5 +/- 1.7 h), and was longest in medium cages (6.2 +/- 2.6 h) at low mosquito densities (5.8 +/- 2.8 h). Biting rate was influenced by mosquito density and the time of observation (0800, 1200, 1600 h) in Ae. aegypti, but not An. quadrimaculatus, and in both species was a significant predictor of MDPB. When a standard dose of deet (1 ml, 25% in ethanol on 650 cm2 of skin) was used, large cages with high densities of mosquitoes resulted in the shortest repellent protection times; medium cages with low mosquito densities resulted in the longest protection times.