Potential of some volatile oils in protecting packages of irradiated wheat flour against Ephestia kuehniella and Tribolium castaneum

Six essential oils of Citrus reticulate (mandarin peel), Pimpinella anisum (anise), Anethum graveolens (dill), Allium sativum (garlic), Ocimum basilicum (basil) and Zingiber officinale (ginger), were evaluated for fumigant toxicity against Ephestia kuehniella and Tribolium castaneum and for contact toxicity against larvae of both species. The major compounds in these volatile oils were identified using gas chromatography- mass spectrometry. Both O. basilicum and Z. officinale oils gave 100% mortality within 24 h with doses of 32 μl/l air for E. kuehniella adults, and 128 μl/l air for T. castaneum adults. The oil of A. graveolens was the most effective against larvae of both species; treated filter papers giving 100% mortality of T. castaneum and E. kuehniella larvae with exposure periods of 24 h and 96 h, respectively. The persistence of toxicity of the six tested oils varied according to their chemical components with A. graveolens and O. basilicum proving the most persistent, and C. reticulate and P. anisum the least. The possible use of the oils applied as a 30% aqueous solution for protection of wheat flour irradiated with gamma radiation (1.5 KGy) from infestation by the test insect species during a 60-day storage period in damour and gunny plastic pouches was investigated. The effect of these oils on acetylcholinesterase activity also was examined to explore their possible mode of toxic action. Dill oil was the most active against E. kuehniella larvae while ginger oil had the greatest depressive action against T. castaneum larvae.

► This study was conducted to determine the insecticidal activity of six volatile oils against two stored product insects.
► The major compounds in these volatile oils were identified using gas chromatography-mass spectrometry.
► Persistence of insecticidal activity of six volatile oils was in relation with their chemical composition.
► Six volatile oils are monoterpenoids or sulphur compounds were inhibited acetylcholinesterase.
►  Gamma irradiation was used to disinfest flour in damour packages.