author(s)
Alanazi Naimah Asid, Khaled M Al-Ghamdi, Mangoud AAH, Khaled Al Asiry, NA Alkenani and Yasir Anwar

abstract
The present research was undertaken to study the synergistic effect of 3 pyrethroid and 3 organophosphorus insecticides against field strain of the females and the 2^nd larval instars of the housefly, M. domestica using CDC bottle and dipping application bioassay techniques under laboratory conditions, respectively. It was found that pyrethroid insecticides, Cypermethrin and Cyfluthrin showed the highest co-toxicity factor 14.4, while the lowest co-toxicity factor was 1.5. Whereas, the preliminary toxicity screening of the three organophosphorus insecticides (Diazinon, Propetamphos and Pirimiphos methyl) against M. domestica 2^nd larval instar showed additive effects with different degrees according to the estimated co-toxicity factor. The mixture of Diazinon and Pirimiphos methyl showed the highest co-toxicity factor 8.10. So it is concluded that mixture of these chemicals has better insecticidal effect against the housefly compare to alone and can be used for the control of housefly.