The comparative toxicity of ten selected native essential and
edible oils was assessed against S. granarius. The oils used are black seed
oil (Nigella sativa), Sesame oil (Sesamum indicum), olive oil (Olea
europaea), Peppermint oil (Mentha piperita), Basil Oil (Ocimum
basilicum), orange oil (Citrus sinensis), Rosemary oil (Rosmarinus
officinalis), Clove oil (Dianthus caryophyllus), Garlic oil (Allium
sativum), and Cinnamon oil (Cinnamomum zeylanicum). Different
concentrations of oils were mixed with wheat grains and provided for
adults in test tubes. Mortalities were recorded for 3 days post-treatment.
The overall results showed that Garlic oil was the most toxic and
Rosemary was the least toxic among both edible and essential oils. A
direct correlation was found between oil dose and percent mortality of
adults under all exposure periods. The recorded values of LC50 and the
toxicity index showed that Sesame oil was the most toxic edible oil
followed by Black seed and Olive oils. The essential oils used can be
arranged in descending order according to their toxicities to S. granarius
adults as follows: Garlic > clove > Cinnamon > Basil > Orange >
Peppermint> Rosemary. All the fixed and essential oils used,
demonstrated satisfactory activity and proved to be promising as control
agents of S. granaries and consequently other similar stored product
insects. Some oils were highly toxic at low concentration and short
exposure time; whereas some oils might be required in higher
concentrations and longer exposure time to achieve satisfactory control
of the insects.
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