In September 1989, four weekly ULV applications of PESGUARD-PS (Pyrethroid) with SEMCO car mounted ULV aerosol generator in Pout (Thiès, Sénégal) were ineffective against adult populations of Anopheles arabiensis, Culex quinquefasciatus and others culicines. No decrease in the mosquito populations was observed both indoor and out door in the test area.