Chemical composition, toxicity, and repellency of some Myrtaceae plants essential oils against Tribolium castaneum (Herbst)

Abstract

Essential oils (EOs) obtained from plants have the potential to be environment-friendly alternatives to synthetic insecticides in agriculture. Tribolium castaneum (Herbst) is a cosmopolitan pest that causes the loss of a major proportion of stored crops. Therefore, we studied the insecticidal and repellent effects of EOs derived from the plants viz. Eucalyptus rudis, Eucalyptus crebra, and Melaleuca genistifolia against larvae and adults of T. castaneum. Essential oils were derived from the leaves of each plant using hydro-distillation. Gas chromatography-mass spectrometry (GC-MS) of the extracted EOs revealed that eucalyptol, viridiflorol, α-terpineol, and eugenol methyl comprised the major components of the EOs. However, the composition and quantity of the compounds varied across EOs. Specifically, EOs derived from E. rudis exhibited the highest fumigation toxicity against adult and larval T. castaneum, followed by M. genistifolia and E. crebra. In the presence of wheat grains, fumigation toxicity against T. castaneum declined by nearly threefold. Contact toxicity assays revealed that EOs from E. rudis were overall the most effective against the pest (LC50: 0.392 μL/cm2 for adult; LC50: 0.471 μL/cm2 for larva) followed by M. genistifolia (LC50: 0.424 μL/cm2 for adult; LC50: 0.478 μL/cm2 for larva) and E. crebra (LC50: 0.471 μL/cm2 for adult; LC50: 0.515 μL/cm2 for larva). The LC50 value of each EO was up to five times lower in adults than in larvae. Melaleuca genistifolia was the most effective repellent against T. castaneum adults; however, its effectiveness decreased with increasing exposure time. In conclusion, the EOs of E. rudis, E. crebra, and M. genistifolia were all viable green biopesticide alternatives to synthetic insecticides.