Bioactivity of short-chain aliphatic ketones against adults of the granary weevil, Sitophilus granarius (L.).

The granary weevil, Sitophilus granarius (L.), is one of the most damaging pests of stored grains, causing severe quantitative and qualitative losses. Sustainable control means, alternative to the commonly used fumigants and broad-spectrum contact insecticides, are urgently needed owing to legislative limits, the development of resistant insect strains and increasing consumer demand for safe food. Short-chain aliphatic ketones, known to be emitted by cereal grains and previously identified as repellents to adult granary weevils, were evaluated for their ability to disrupt insect orientation towards wheat grains and as possible natural fumigants. In behavioural bioassays, 2-pentanone, 2-hexanone, 2-heptanone and 2,3-butanedione significantly reduced insect orientation towards odours of wheat grains, with 2-hexanone and 2-heptanone being the most active. In fumigation tests, all compounds were effective in killing weevil adults, but they performed differently according to chemical structure, speed of action and presence of wheat grains. In the presence of grains, the highest fumigant toxicity was shown by 2-pentanone (LC(50) = 8.4 ± 1.0 mg L(-1)) after 24 h exposure, and by 2-pentanone (LC(50) = 4.5 ± 0.3 mg L(-1)), 2-heptanone (LC(50) = 7.1 ± 0.3 mg L(-1) ) and 2-hexanone (LC(50) = 8.1 ± 0.6 mg L(-1)) 1 week after the treatment end. Short-chain aliphatic ketones have potential for applications in IPM programmes for the granary weevil because of their behaviour-altering activity and fumigant toxicity.