Four insecticides were evaluated in the .open field for their efficacy against , whitefly Bemisia tabaci on tomato plants. Two of insecticides (pirtmlphos-rnethyt
and chlorpyriphos-ethyl) were ·fror:n organophosphorus compounds, and the other
two (cypermethrin and fenv?lerate) from pyrethroids. Two sprays were applied for
these insecticides at the recommended rates. Reduction percentages of whitefly
populatlonat.different intervals (an hour, 1,3, 7 and 15 days) were estimated. Data . of first spray showed that the means of whitefly were high after an hour of spray then
reduced in all insecticide treatments- afterwards except on third day of pirirniphos-
methyl treatment. The maximum percent of reduction reached 65.64% in pirimiphos-
methyl treatment along 15 days when compared with control. After the second spray,
the percent of reduction were 70.42, 62.90, 57.82 and 49.98 in chlorpyrifos-ethyl,
pirimiphos-methyl, fenvalerate and cyperrnethrin, respectively along 15 days
compared with control.. None of lnsecticide treatments gave complete reduction of
whitefly at any time of insecticide treatment