Designing of a laboratory model for evaluation of the residual effects of deltamethrin (K-othrine WP 5%) on different surfaces against malaria vector, Anopheles stephensi (diptera: culicidae).

BACKGROUND & OBJECTIVES Deltamethrin plays an important role in controlling malaria vectors, and is used in indoor residual spraying and manufacture of long-lasting insecticidal mosquito nets. The residual activity of deltamethrin (K-othrine WP 5%) @ 25 mg/m(2) was studied in laboratory conditions on different surfaces. METHODS The surfaces were made artificially with different building materials such as mud, plaster, cement and wood in the laboratory. The surfaces were mounted inside petri-dishes (diam: 20 cm) and wood surface was prepared separately. The prepared surfaces were attached to the walls and deltamethrin was applied using standard Hudson pump sprayer with a discharge rate of 757 ml/ min or 0.2 gal/min. The spraying was conducted at standard rhythm as recommended by WHO. After application all the sprayed surfaces were transferred into the special wooden boxes designed for this purpose. The surfaces were maintained at laboratory conditions. The WHO's recommended bioassay kit and method was used during this study. RESULTS Bioassays on Anopheles stephensi Liston showed that the persistence of deltamethrin on different surfaces (>70% mortality) was around 4 months on plaster (Mortality = 77+/-6.2%), 2 months on mud (76.9+/-6.8%), 4.5 months on cement (79+/-3.2%), 4 months on wood (71.7+/-6.8%) and 4 months on filter papers (82.3+/-5.4%). INTERPRETATION & CONCLUSION The results of this study on residual effects of deltamethrin WP 5% (25 mg/m(2)) are highly concordant with two field bioassays carried out in a malarious area at south-eastern Iran. This method can be replaced by the field bioassay tests which are time consuming and costlier.