Repellence and fumigant toxicity of propionic acid against adults of Sitophilus granarius (L.) and S. oryzae (L.)

The biological activity of propionic acid towards adults of the primary stored-grain pests, Sitophilus granarius and S. oryzae was investigated by electroantennographic, behavioural and fumigant toxicity assays. Electroantennograms revealed the sensitivity of both sexes of the two species to propionic acid. In two-choice pitfall bioassays, the compound showed dose-dependent repellent effects even in the presence of wheat odours, which attracted the beetles. In the fumigation assay, propionic acid was effective in killing weevil adults. The LC50 values, calculated for both species at 23 and 30 °C, ranged from 5 to 10 μg/L air and are comparable to those of other known fumigants. Propionic acid could have potential for applications in IPM programs for stored-grain beetles because of its safety, high volatility, repellency and fumigant activity.