Comparative evaluation of persistence and residue of deltamethrin and cyfluthrin on different surfaces at Iranshahr area in Sistan & Baluchistan province in Iran 2004-2005

Background: Malaria is still one of the health problems in Iran. Resistance of Anopheles stephensi -the principal vector of the disease in the southeast of Iran- to insecticides such as DDT, malathion and dieldrin has been reported in south of the country. The present study was designed to estimate the persistence and residue of deltamethrin and cyfluthrin on different surfaces. Methods: After testing the surface of selected locations for previous insecticides, 4 locations were sprayed with deltamethrin (25 mg/m2) and cyfluthrin (20 mg/m2). A total of 22 conical tubes were installed and fixed on surfaces of walls and ceilings made from plaster, mud and wood. In each conical tube, 10 An. stephensi were released and after half an hour exposure these mosquitoes were transmitted to sterile cups. After 24 hours, the obtained results were recorded according to the survival and mortality rate of mosquitoes. These tests were carried out from 5 days after spraying and repeated every 15 days until the mortality rate decreased to 60-65%. Results: Persistence and residue rate of deltamethrin 5% with the scale of 25 mg/m2 of effective substance was 3 months at most. Afterwards persistence and residue effect of this insecticide decreased on absorbent and nonabsorbent surfaces. Persistence and residue rate of deltamethrin 10% with the scale of 20 mg/m2 on absorbent and nonabsorbent surfaces in Sistan & Baluchistan province climate was estimated 2.5 months. Afterwards, its persistence and residue effect decreased significantly. In the sprayed locations with deltamethrin, there was no correlation between the An. stephensi mortality and absorbent (plaster and muddy) and nonabsorbent (wooden) surfaces (P>0.05). Also, in locations sprayed with cyfluthrin there was no significant correlation between the two types of surfaces, however, the mortality rate was significantly different between plaster and muddy surfaces (P=0.007). Moreover, from the point of residual efficacy, there was a remarkable correlation between deltamethrin and cyfluthrin (P