Abstract
Essential oils, when used as bio-insecticides in the control of insect pests of stored grains have shown specificity and variation in the potentiality of their mode of action. In the present study, three essential oils extracted from three aromatic plants of different families, white wormwood (Artemisia herba alba, Asteraceae), oregano (Origanum vulgare, Lamiaceae) and rue (Ruta montana, Rutaceae), were evaluated for their repellent and fumigant toxic potential against the flour moth larvae, Ephestia kuehniella (Lepidoptera, Pyralidae), under laboratory conditions. The essential oils extraction was done by the hydrodistillation method. The repellent activity was carried out in Petri dishes using a filter paper treated with different oil dilutions (25, 75, 100, 120, 130, 150 µL/mL). The fumigant toxicity was determined on three concentrations (50, 130, 150 µL/L air). Two plants were shown to be repellent against the E. kuehniella larvae. Origanum oil was the most repellent with 67% of repellency rate followed by Artemisia oil (46%) at 120µL/mL after 2 hours of exposure. The oil of R. montana had an attractant activity against the larvae and was the most toxic with 56.7% of larval mortality in the first 24 hours. The median lethal concentrations (LC50) recorded were 11.6, 175.4 and 1100.0 µL/L air for the plant oils R. montana, O. vulgare and A. herba alba, respectively. R. montana and O. vulgare essential oil are shown to be efficient with high toxic and repellent properties against E. kuehniella larvae. Their specific potential could be integrated in the selection of the best bioinsecticides for the optimum protection of stored grain.
Highlights
Attacks by insect pests of stored grain, in term of quantity and quality of the product, are not negligible
According to the index of preference, the negative values indicated that A. herba alba and O. vulgare were repellent against E. kuehniella during 30, 60, 90 and 120 mn (Fig. 1)
R. montana exhibited attractant effect according to preference index
Summary
Attacks by insect pests of stored grain, in term of quantity and quality of the product, are not negligible. Plant essential oils are volatile active substances extracted from aromatic plants that belong to many higher plant families, Liliaceae, Apiaceae, Pinaceae, Myrtaceae, Lamiaceae, Asteraceae, Rutaceae and Lauraceae. Due to their volatility, essential oils are environmentally non-persistent and ‘generally recognized as safe’ by the United States Food and Drug Administration (Tripathi et al, 2009). Concentrations of active chemical compounds often vary between plant family, within the same plant species and between plant parts (leaf, seed, root, fruit, flowers, bark, etc.). According to Jayakumar et al (2017), plants have well developed defence mechanisms against pests due to the intensity of plant-insect interactions, and are excellent sources of new insecticidal substances
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