Fenthion (O,O-dimethylO-[4-(methylthio)-m-tolyl] phosphorothioate) applied by airplane at a rate of 56.0 g/ha (20.8 ml mixed in one liter fuel oil) to control mosquito larvae on 14,164 ha of mountain meadow ranchland in the Little Laramie Valley, Wyoming, had relatively little adverse effect on honey bees,Apis melliferaL. Although the material is highly toxic to the bees, exposed colonies had only partial, nonincapacitating loss of the field force that lasted only one day. Brood production, number of frames of adult bees, and pollen collection were not affected. Therefore, in a similar situation, it would not be necessary or practical for a commercial beekeeper to move his colonies during application of this insecticide.