The efficiency of petroleum ether extracts of black pepper and dill seeds and clove fruits were investigated separately and under phosphine treatment at two temperatures of 30 and 15°C against the lesser grain borer, Rhizopertha dominica (F.) in the laboratory. The results indicated relatively very high rates of adults mortality (90 100 %) after 7 days from the initial treatment at 30°C with the two tested concentrations (0.25 and 0.5 % w/w) of the various extracts. At lower temperature (15°C), the corresponding mortality rates ranged froni 81.7-100 %. This result revealed that the tested materials were highly effective against this insect species. Thus, these VarIOUS plant extracts could be used successfully as grain protectants against this insect species especially at 0.5 % w/w concentration. Applying of the various plant extracts under phosphine treatment produced generally greater adults mortality rates than each component separately at longer exposure (5 and 7 days) for the two tested concentrations of the various plant extracts. The results of joint action resulting from the combined treatments of the plant extract in the presence of phosphine showed additive effects for longer exposure periods of 5 and 7 days at the two tested temperatures, while at shorter period (3 days) either an antagonistic or additive effect was noticed.