Insecticidal efficiency of selected essential oils against stored pests Sitophilus orzyae and Callosobruchus...

Insect pests impose considerable damage on stored grains and food products globally, leading to a decrease in their weight, quality, and market value. Historically, various herbs and spices, including turmeric, garlic, and cloves, have been utilized to control storage pests. The biological effects of essential oils were determined by various bioassays to measure their contact and fumigant toxicities, as well as their repellent properties. This study expected to determine the efficacy of essential oils from selected plants, such as Nigella sativa (black cumin), Syzygium aromaticum (clove oil), and Zingiber officinale (ginger), in repelling and killing two major insect pests of stored grains: the cowpea weevil (Callosobruchus maculatus) and the rice weevil (Sitophilus oryzae). The essential oils were extracted by decoction method, and ethylene was used as a solvent. The oils were applied individually to small pieces of Whatman No. 1 filter paper at dosages of 5, 10, 15, and 20 µl/L of oil. Twenty insect pests were placed in Petri dishes, and the mortality rate for each treatment was recorded, with LC₅₀ values calculated. Each experiment was replicated three times. The results directed that S. aromaticum exhibited a high mortality rate against both the cowpea weevil (300) and the rice weevil (300), with repellent effects observed at various concentrations (1, 5, and 10 µl), which helps to prevent weevil invasion in stored grains and legumes. The mortality rate of the pests was directly related to the concentration of the essential oil. Essential oil extracts from Nigella sativa were important in controlling rice weevils (Sitophilus oryzae), while Syzygium aromaticum is active against cowpea weevils (Callosobruchus maculatus) due to the varied chemical components in their essential oils. Zingiber officinale showed reasonable insecticidal activity, but Syzygium aromaticum displayed greater repellent potential against both S. oryzae and C. maculatus.