Toxicity of Melaleuca rhaphiophylla essential oils against Sitophilus zeamais and Sitophilus oryzae

Abstract

The Melaleuca genus has insecticidal activity against agricultural pests. In particular, Melaleuca rhaphiophylla essential oil (MREO) showed high toxicity against some stored product weevils in a short period. Therefore, the present study aimed to evaluate the sublethal dose and the effect on biochemical markers of MREO and its emulsion (MREM) against Sitophilus zeamais and Sitophilus oryzae. The emulsion was prepared by combining hydroxypropyl methylcellulose (HPMC) (2 wt%) with MREO to concentrations of 39.18 and 25.61 μL of substance L⁻¹ of air for S. zeamais and S. oryzae, respectively. The insecticidal activity of both MREO and MREM was evaluated by the fumigation method, followed by the determination of Glutathione S-Transferase (GST), esterase-α, esterase-β, superoxide dismutase (SOD), acetylcholinesterase (AChE) activities, and lipid peroxidation (LPO). The MREO caused a mortality rate above 25%, with an increase of AChE and LPO for both species, there was altered esterase-α for S. zeamais and inhibition of GST, esterase-α, esterase-β and SOD activity for S. oryzae. Meanwhile, the MREM caused a mortality rate of less than 1.5%, with an increase in GST, SOD, and LPO enzymes for both species, and an increase in the enzymatic activity of esterase-α for S. oryzae. Therefore, we concluded that MREO demonstrated higher insecticidal activity, while MREM caused continuous toxicity at fragmented doses caused by emulsion exposure, stimulating detoxification and resistance mechanisms.