Insecticidal potential of essential oil from inflorescences of Etlingera elatior and its major constituents against Sitophilus zeamais

The maize weevil, Sitophilus zeamais, is responsible for an estimated 15 to 40 % loss of corn kernels in the field and during storage. Phosphine-based fumigants and insecticides, such as pyretroids and organophosphates, have been employed excessively for the control of this pest, causing harm to the environment. Botanical products have been analyzed as safer, more viable alternatives. The present study investigated the insecticidal effect against S. zeamais of the essential oil from the inflorescences of Etlingera elatior (EeIEO) and its two major constituents. EeIEO was extracted by hydrodistillation and characterized using gas chromatography techniques (GC and GC/MS). Dodecanal (58.31 %), dodecanol (20.33 %), β-caryophylene (4.21 %), α-pinene (2.66 %), n-decanol (2.52 %) and β-farnesene (2.46 %) were the main compounds found in the oil. EeIEO, dodecanal (NAL) and dodecanol (NOL) exhibited toxicity by fumigation (LC50 = 0.83, 0.51 and 3.05 μL/L of air, respectively) and contact (LD50 = 1.42, 1.04 and 0.28 μg/adult, respectively) for adult forms of S. zeamais. All nutritional parameters of the insects were altered by the ingestion of an artificial diet mixed with EeIEO, NAL and NOL, which promoted insect mortality and had a strong deterrent action (feeding deterrent indices from 70.5 to 92.0 %). EeIEO, NAL, and NOL were also capable of inhibiting in at least 67 % amylase activity from the insect gut. The results indicate the insecticidal activity of EeIEO, NAL, and NOL as a natural option for the control of S. zeamais. NOL achieved the best results in terms of toxicity by contact and ingestion, whereas NAL was the most effective by fumigation.