Phytochemical Characterization of Callistemon lanceolatus Leaf Essential Oils and Their Application as Sustainable Stored Grain Protectants against Major Storage Insect Pests

Food storage has been important since the dawn of agriculture and human settlement. Insect pests cause major losses to food grains during storage and production. Essential oils are good alternatives for chemical insecticides for the management of storage pests. Red bottlebrush, Callistemon lanceolatus, is a flowering plant of the Myrtaceae family. This research work aimed to extract the oil from bottlebrush leaves, and chemically characterize and assess their repellent and insecticidal properties against the cowpea seed beetle, Callasobruchus maculatus (F.) (Coleoptera: Chrysomelidae), cigarette beetle, Lasioderma serricorne (F.) (Coleoptera: Ptinidae), and red flour beetle, Tribolium castaneum (Herbst.) (Coleoptera: Tenebrionidae), for the first time. The essential oil yielded by hydro-distillation of bottlebrush leaves was 1.02 ± 0.01%. GC-MS analysis determined the chemical composition of the volatile oil comprised 1,8-cineole (19.17%), α-terpineol (11.51%), α-pinene (10.28%), and α-Phellandrene (9.55%). The C. lanceolatus leaf oil showed potent repellence, contact toxicity, and fumigation toxic effects. In the contact toxicity assay, at 24 h, the LC₅₀ values were 1.35, 0.52, and 0.58 mg/cm² for the red flour beetle, cigarette beetle, and cowpea seed beetle, respectively. Likewise, in the fumigation assay observed after 24 h, LC₅₀ values of 22.60, 5.48, and 1.43 µL/L air were demonstrated for the red flour beetle, cigarette beetle, and cowpea seed beetle, respectively. Additionally, there was no significance found by a phytotoxicity assay when the paddy seeds were exposed to C. lanceolatus oil. The results show that the volatile oils from red bottlebrush leaves have the potential to be applied as a biopesticide. Therefore, C. lanceolatus leaf oil can be utilized as a bio-insecticide to control stored product insects.