Residual toxicity of deltamethrin and permethrin on various surfaces for mosquito species culex pipiens molestul Forskal.

The culicine mosquito species Culex pipiens molestus Forskal were exposed by tarsal contact to various surfaces sprayed with the photostable synthetic pyrethroid preparations deltamethrin (NRDC 161) and permethrin (NRDC 143) used in the form of emulsifiable concentrates (EC) and wettable powders (WP) at doses 0.001, 0.005, 0.02, 0.1 and 0.5 g/m2. The time to appearance of the knock down effect and the residual toxicity were tested for each preparation and type of surface studied. The onset of deltamethrin and permethrin knock down effects was found to be very rapid at higher insecticide doses. The mean KT 100 value for permethrin EC at 0.5 g/m2 and for deltamethrin EC and WP at 0.1 g/m2 measured within the first month after insecticide application were almost invariably below 60 min on all the surfaces tested. Taking the 2-month interval as a sufficiently long period of operationally effective residual activity, the following insecticide doses can be recommended as optimal for the Culex mosquito control inside the dwelling space: deltamethrin EC and WP doses of 0.001 g/m2 for plywood, 0.005 g/m2 for whitewashed surface, 0.02 g/m2 for ceramics, and 0.02 (WP) and 0.1 (EC) g/m2 for limewashed surface; permethrin EC doses of 0.1 g/m2 for all types of surfaces and permethrin WP doses of 0.005 g/m2 for plywood and 0.02 g/m2 for the remaining types of surfaces.