Toxicity of various essential oils and their volatile components against the red flour beetle, Tribolium castaneum (Herbst) was determined. The most potent fumigant toxicity was found in essential oil from rosemary ($ extrm{LD}_{50}$ = $7.8mu extrm{l/l}$ air) followed by the oils of lemon ($ extrm{LD}_{50}$ = $16.2mu extrm{l/l}$ air), basil ($ extrm{LD}_{50}$ = $17.8mu extrm{l/l}$ air), lime ($ extrm{LD}_{50}$ = $17.9mu extrm{l/l}$ air), and peppermint ($ extrm{LD}_{50}$ = $25.8mu extrm{l/l}$ air). 1,8-Cineole was the most toxic fumigant compound found in rosemary essential oil ($ extrm{LD}_{50}$ = $7.4mu extrm{l/l}$ air) followed by menthone ($ extrm{LD}_{50}$ = $8.5mu extrm{l/l}$ air) and p-cymene ($ extrm{LD}_{50}$ : $11.4mu extrm{l/l}$ air). 1,8-Cineole exhibited similar fumigant toxicity against a PH3-resistant T. castaneum relative to the susceptible insects. Therefore, 1,8- cineole and rosemary essential oil could be a safer fumigant to control stored-product insect pests than those currently used.