We describe here an in vitro behavioral assay for testing mosquito repellents applied in a dose-based manner to a warm body (34 degrees C) in test cages. The system was used to assess the sensitivity of 4-6-day-old Anopheles gambiae to the insect repellent diethyl methyl benzamide (deet). These tests were made in the absence and presence of additional carbon dioxide (CO2) applied as a pulse to activate mosquitoes in the cages. In the absence of the CO2 pulse the mosquitoes hardly responded to the warm body. Increasing the CO2 level in the cage by 1,000 parts per million caused a 25-fold increase in the number of landings by mosquitoes on the warm body in 2-min tests. This mosquito activation allowed the measurement of a significant reduction in the number of landings to bite on the warm body with increasing doses of deet (0.4 to 3.8 microg/cm2). An asymptotic nonlinear model fitted to the repellency data in the presence of CO2 allowed estimation of the effective dose of deet that reduced landings to bite by 50% (ED50) at 0.95 microg/cm2 (5 nmol/cm2) and the corresponding ED95 at 4.12 microg/cm2 (21.5 nmol/cm2). This in vitro bioassay has the advantage of permitting a fast throughput of test products under standardized conditions and is suitable for screenings designed for the purpose of discovering lead products with as yet unknown human toxicological and dermatological profiles.
Insecticide-impregnated traps and visual targets are used for tsetse (Diptera, Glossinidae) population control. Such devices are made with textiles and deltamethrin is frequently the insecticide of choice. However, persistence of an insecticide on textiles is affected by exposure to weather. Here we examine the effect of weathering on the capacity of four textiles with increasing proportions of polyester (0, 35, 65, and 100%) with cotton and viscose to retain deltamethrin. Textiles tested were those used to make visual targets in a pan-African program to maximize target efficiency for controlling tsetse vectors of African trypanosomiasis. Following impregnation in an aqueous suspension of deltamethrin at 1,000 mg/m2, textiles were weathered for 18 mo at Lambwe Valley, Kenya and sampled every 3 mo to make knockdown tests on the tsetse fly Glossina pallidipes Austen. Deltamethrin content of the textiles was established using gas chromatography mass-spectrometry at impregnation and after 9 mo of weathering. Textiles with higher proportions of polyester retained deltamethrin better: respectively, 100% polyester and 65:35 polyester/viscose textiles retained deltamethrin at 17 and 11 mg/m2 9-mo post-treatment that caused 100% knockdown in G. pallidipes after 1 h, and killed 67 and 47% of flies, respectively, after 24 h. Eighteen-month weathered 100% polyester treated textile still knocked down all tsetse exposed to it within 2 h. The LD50 for deltamethrin on filter paper for G. pallidipes was estimated at 28.8 mg/m2, indicating that deltamethrin is more available on polyester to kill tsetse.
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