Assessment of insecticidal efficacy of aromatic plant leaf oil extracts on the adults of Sitophilus oryzae Linnaeus 1763 (Coleoptera: Curculionidae) and Tribolium castaneum Herbst 1797 (Coleoptera: Tenebrionidae)

Abstract

Post-harvest infestation of cereals and pulses by insect pests causes serious qualitative and quantitative losses to stored grains. Indiscriminate use of chemical insecticides have led to negative effects on the environment, pest resistance and resurgence, insecticide resistance, emergence of genetically resistant insect strains, chemical residues in food products and human health effects. Plant oils extracted from aromatic plants exhibit a wide range of insecticidal properties and are regarded as safe substitutes for traditional synthetic insecticides against stored grain insect pests. Hence, the objective of this study was to investigate the potential of oils extracted from aromatic plant leaves against two of the most pervasive and damaging insect pests of stored products worldwide, viz., Sitophilus oryzae and Tribolium castaneum. The aromatic plant leaf oil extracts were analyzed for its phytochemical compounds via GC-MS and tested for its toxicity on the adults of S. oryzae and T. castaneum at dosages of 0.62, 1.25, 2.50, 5.00, and 10.00 µL/L by Petri dish filter paper disc bioassay method. Adult mortality was calculated 24, 48 and 72 h after exposure. Azadirachta indica, Chrysopogon zizaniodes, Citrus sinensis and Mentha piperita achieved 100.0 % adult mortality in S. oryzae at 10.00 µL/L after 72 h of exposure, and their respective LD₅₀ values were 1.02, 1.16, 1.38 and 1.50 µL/L. A. indica and Cymbopogon nardus caused a maximum of 96.6 % and 95.8 % adult mortality in T. castaneum, respectively at 10.00 µL/L after 72 h of exposure, and their respective LD₅₀ values were 1.49 and 1.90 µL/L. A. indica, C. nardus, M. piperita and M. fragrans showed pronounced adult mortality and their toxicity factor ranged from 1.00 to 1.58 against both S. oryzae and T. castaneum after 72 h. The major phytocompounds present in the aromatic plant leaf oil extracts belonged to the class of terpenoids and terpenes. The present study highlighted the significance and scope of aromatic plant leaf oil extracts for the management of S. oryzae and T. castaneum in integrated pest management.