Bioactivity, biochemical mechanisms, and olfactory effects of the essential oil from Syzygium aromaticum and its major compound eugenol on Sitophilus zeamais L. (Coleoptera: Curculionidae)

With the significant losses Sitophilus zeamais (Linnaeus, 1763) causes to corn from fields to storage and the harmful effects of excessive chemical insecticide use, this study aimed to assess the toxicity of Syzygium aromaticum essential oil and its main component, eugenol. It also looked into how they impact S. zeamais biochemical profile over time. The study analyzed chromatographic data for the oil and various parameters for the insects, including mortality rates, repellence, deterrence, adult emergence, and biochemical changes (proteins, lipids, sugars, and glycogen levels). Results showed that S. aromaticum essential oil had a significant lethal effect on S. zeamais , with an LC ₉₅ of 35.21 µL/L and an LC ₅₀ of 13.7 µL/L, while eugenol's LC ₉₅ was 12.74 µL/L and its LC ₅₀ was 7.33 µL/L in contact toxicity tests. Both the oil and eugenol demonstrated repellent and fumigant effects, disrupting the insect's biology. In terms of nutritional impact, the substances affected the insects differently. The essential oil initially increased nutrient levels but then reduced them after 48 hours, while eugenol initially increased levels but eventually led to a decrease. In conclusion, both the essential oil and eugenol showed adverse effects on S. zeamais , altering crucial survival parameters. However, eugenol yielded more significant results and is readily available commercially, making it a promising candidate for developing new insecticidal products.