Abstract
Base line data of susceptibility of a laboratory reared strain of Musca domestica to dichlorvos 50EC and
chlorpyrifos 40EC in a range of concentrations from 250 to 5000 ppm of the formulated insecticides in acetone
was determined. These concentrations in a volume of 5 ml were added to 25 gm of granulated sugar in a petri
dish. Sesame oil was used, as the synergist. Insecticide was mixed with sesame oil in 1:1 and 1:2 ratio to obtain
KDsdLCso of the insecticide + synergist combination. House fly was allowed to feed on the insecticide coated
sugar for 48 hr. Knockdown and mortality data was observed after 1, 2, 4, 6, 8, 12, 24 and 48 hours. The results
showed that dichlorvos was the most effective with LCso value, 122 ppm and with the synergist combination, none
of the two insecticides proved effective. Toxicity relationship of these insecticides with sesame oil is discussed
Key words: dichlorvos; chlorpyrifos; bioassay via feeding; Musca domestica; synergist, sesame oil
