Comparative repellency of commercial formulations of deet, permethrin and citronellal against the mosquito Aedes aegypti, using a collagen membrane technique compared with human arm tests.

A collagen membrane technique, based on the membrane blood-feeding system of Cosgrove et al. (1994), was used to compare repellents against Aedes aegypti mosquitoes. Repellency was defined in terms of inhibition of probing (ED50 and ED90) after 5 min exposure. A direct comparison was made with repellency from probing after 5 min on five male volunteers. Four repellent products were compared with technical DEET as the standard. The liquid formulations tested were: Autan (20% deet; Bayer); Repel Plus (20% deet plus 0.05% permethrin; Boots); permethrin (Zeneca) and citronellal (Sigma). Membrane and arm tests gave similar results. Deet formulations required less active compound than citronellal for the same degree of repellency. Pure deet and Autan gave similar results, dose for dose. Permethrin was highly repellent at very low doses, but Repel Plus did not enhance the immediate repellency of deet. A technique using the same membrane system was developed to evaluate persistence of Autan, which declined to 75% after 1 h against Ae. aegypti, and to about 50% after 2-4 h.