Efficacy of propionic acid against the granary weevil <i>Sitophilus granarius</i> (L.)

Abstract

Propionic acid is used to preserve feed grain, especially against fungal attack, and is known to affect stored product insects as well. In the study presented here, the effect of wheat treated with different amounts of pure propionic acid on both adult Sitophilus granarius and its progeny was investigated. Propionic acid (99.5% purity) was added to samples of 150 g of wheat at the doses of 0.5, 0.7 and 1% by weight. Subsequently, 100 adult S. granarius were released into each vial with treated wheat. Each trial was repeated three times. The untreated controls received water instead of propionic acid. Dead weevils were counted after 7 and 14 days. Insects surviving 7 days were placed back into the vials, all adults were removed after 14 days. During the period of 8 and 11 weeks after start of the experiment, the number of progeny was counted weekly. In the trials with 0.5%, 0.7% and 1% by weight, after 14 days 73.7, 37.3 and 3.7% of the adults were alive, respectively. While the mean number of progeny was 1549 in the untreated control, 1.3 and 0.3 progeny on average emerged from the grain treated with 0.5% and 0.7% propionic acid, respectively. No progeny survived in the treatment with 1% by weight. Even though complete control of adult S. granarius could not be achieved with the tested conditions, under practical situations of storage of feed grain, the described application of propionic acid will effectively suppress the mass-development of S. granarius.

Keywords: Granary weevil, Sitophilus granarius, Propionic acid, Control, Feed storage