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item Barnard, Donald

Submitted to: Journal of the American Mosquito Control Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/19/2002
Publication Date: 12/1/2005
Citation: Barnard, D.R. 2005. BIOLOGICAL ASSAY METHODS FOR MOSQUITO REPELLENTS. Journal of the American Mosquito Control Association. 21:12-16.

Interpretive Summary: Before mosquito repellents become available to the consumer, scientists test them extensively to determine if they are safe and effective. In the case of a new repellent, the decision to proceed with development is based on the results of laboratory tests called bioassays. Many repellent bioassay protocols have been developed in the last 40 years but differences in the protocols preclude a reliable comparison of test results from different methods. To correct this situation, the U.S. Environmental Protection Agency (EPA) developed guidelines for the bioassay of commercial mosquito repellent products. While developing these guidelines, EPA officials requested ARS scientists at the Center for Medical, Agricultural, and Veterinary Entomology in Gainesville, FL to compile the scientific literature on this subject and to write a review article on repellent bioassay methods for scientific publication. Described in this review article are the techniques that have been devised to date for testing mosquito repellents, the technical strengths and weaknesses of each of the techniques, and a listing and discussion of the biological and environmental factors that cause variation in the results of repellents bioassays. The information in the review is used by the EPA, by the scientific community, and by the repellents industry as a basis for performing standardized bioassays. It benefits the consumer public, as well, because standardized testing results in accurate and reliable claims on the product label regarding repellent protection time.

Technical Abstract: Three biological assay procedures for repellents are currently documented in the literature: (1) ASTM E951-94 "Laboratory Testing of Non-Commercial Repellant Formulations on the Skin." (2) ASTM E939-94 "Field Testing Topical Applications of Compounds as Repellents for Medically Important and Pest Arthropods. 1. Mosquitoes." (3) WHO/CTD/WHOPES/IC/96.1 "Report of WHOPES Informal Consultation on the Evaluation and Testing of Insecticides." One public draft set of repellent testing guidelines is available on the internet: (4) USEPA OPPTS 810.3700 "Product Performance Test Guidelines. Insect Repellents for Human Skin and Outdoor Premises." In practice, the outcome of a repellent bioassay using any of these procedures is affected by the absorption, penetration, and chemical modification of repellent on skin and by evaporation, abrasion, and perspiration. Other abiotic factors that influence mosquito responses to repellent stimuli are light, temperature, humidity, repellent dose, exposure time, and test cage shape and size. Biotic variables in repellent bioassays are larval nutrition, carbohydrate availability for adult mosquitoes, age and parity of females, and differences in the innate attraction/repellency of test subjects. Geographic location and seasonal and diel activity cycles in mosquitoes determine when and where repellents can be tested in the field. Critical knowledge of these sources of variation can be converted to improved precision and accuracy in repellent bioassays and the resulting information used to efficiently select new repellent compounds for toxicological evaluation and field testing.