IS THE EXTRACT FROM THE PLANT CATMINT (NEPETA CATARIA) REPELLENT TO MOSQUITOES IN AUSTRALIA?

The worldwide threat of arthropod-transmitted diseases, with their associated morbidity and mortality, underscores the need for effective insect repellents. Multiple chemical, botanical, and "alternative" repellent products are marketed to consumers. We sought to determine which products available in the United States provide reliable and prolonged complete protection from mosquito bites. We conducted studies involving 15 volunteers to test the relative efficacy of seven botanical insect repellents; four products containing N,N-diethyl-m-toluamide, now called N,N-diethyl-3-methylbenzamide (DEET); a repellent containing IR3535 (ethyl butylacetylaminopropionate); three repellent-impregnated wristbands; and a moisturizer that is commonly claimed to have repellent effects. These products were tested in a controlled laboratory environment in which the species of the mosquitoes, their age, their degree of hunger, the humidity, the temperature, and the light-dark cycle were all kept constant. DEET-based products provided complete protection for the longest duration. Higher concentrations of DEET provided longer-lasting protection. A formulation containing 23.8 percent DEET had a mean complete-protection time of 301.5 minutes. A soybean-oil-based repellent protected against mosquito bites for an average of 94.6 minutes. The IR3535-based repellent protected for an average of 22.9 minutes. All other botanical repellents we tested provided protection for a mean duration of less than 20 minutes. Repellent-impregnated wristbands offered no protection. Currently available non-DEET repellents do not provide protection for durations similar to those of DEET-based repellents and cannot be relied on to provide prolonged protection in environments where mosquito-borne diseases are a substantial threat.

This paper is intended to provide the clinician with the detailed and scientific information needed to advise patients who seek safe and effective ways of preventing mosquito bites. For this review, clinical and analytical data were selected from peer-reviewed research studies and review articles, case reports, entomology texts and journals, and government and industry publications. Relevant information was identified through a search of the MEDLINE database, the World Wide Web, the Mosquito-L electronic mailing list, and the Extension Toxicology Network database; selected U.S. Army, U.S. Environmental Protection Agency, and U.S. Department of Agriculture publications were also reviewed. N,N-diethyl-3-methylbenzamide (DEET) is the most effective, and best studied, insect repellent currently on the market. This substance has a remarkable safety profile after 40 years of worldwide use, but toxic reactions can occur (usually when the product is misused). When DEET-based repellents are applied in combination with permethrin-treated clothing, protection against bites of nearly 100% can be achieved. Plant-based repellents are generally less effective than DEET-based products. Ultrasonic devices, outdoor bug "zappers," and bat houses are not effective against mosquitoes. Highly sensitive persons may want to take oral antihistamines to minimize cutaneous reactions to mosquito bites.

The repellency of different concentrations (5, 10, 25, 50, 75, and 100%) and combinations of 5 essential oils (Bourbon geranium, cedarwood, clove, peppermint, and thyme) to Aedes aegypti (L.) and Anopheles albimanus Wiedemann when applied to human skin was determined in laboratory tests. Cedarwood oil failed to repel mosquitoes and only high concentrations of peppermint oil repelled Ae. aegypti. None of the oils tested prevented mosquito bite when used at the 5 or 10% concentration. Thyme and clove oils were the most effective mosquito repellents and provided 1 1/2 to 3 1/2 h of protection, depending on oil concentration. Clove oil (50%) combined with geranium oil (50%) or with thyme oil (50%) prevented biting by An. albimanus for 1 1/4 to 2 1/2 h. The potential for using essential oils as topical mosquito repellents may be limited by user acceptability; clove, thyme, and peppermint oils can be irritating to the skin, whereas both human subjects in this study judged the odor of clove and thyme oils unacceptable at concentrations > or = 25%.