Barely cultivar compositions influence essential oils effectiveness on Sitophilus granarius (L.) (Coleoptera: Curculionidae)

Barley (Hordeum vulgare L.) is one of the most crucial grains for brewing, human nutrition, and animal feeding. It is frequently infested by a pest known as the granary weevil, Sitophilus granarius (L.) (Coleoptera: Curculionidae). The nutritional quality, weight and germination potential of the infested grains can be significantly decreased. Thus, the aim of the current study was to test the combined effects of essential oils (EOs) from two plant species, Dracocephalum kotschyi Boiss. and Dracocephalum multicaule Montbr & Auch (Lamiaceae), and ten cultivars (Abidar, Ansar, Azaran, Bahman, Dasht, Golchin, Makuyi, Nowbahar, Oksin, and Sahra) of barely on the granary weevil. Plant EOs were isolated by the Clevenger apparatus and subjected to GC-MS analysis. Our findings demonstrated that limonene was the predominant component in D. kotschyi and D. multicaule EOs, with 39.96% and 55.25%, respectively. The results indicated that, 24 h after exposure, D. kotschyi had the highest toxicity for the weevils reared on Makuyi (LC50 = 3.84 mu l/l air) and the lowest on Golchin (LC50 = 32.61 mu l/l air). Almost the same pattern was found when D. multicaule EOs were used; the highest and lowest toxicities were on Makuyi and Golchin cultivars, respectively. There were significant variations in the death rate of the weevil on ten barley cultivars exposed to different concentrations of EOs (0, 2, 5, 7, 10, and 13 mu l/l air). It can be concluded that the weevils reared on Makuyi were more susceptible to D. multicaule and D. kotschyi EOs than those reared on other cultivars. Thus, Makuyi cultivar has great potential to be cultivated by farmers in order to combat this insect pest in storage areas.