Óleo essencial de Lippia grata Schauer (alecrim-do-mato): potencial inseticida e repelente contra Chrysomya megacephala (Fabricius, 1794) em condições laboratoriais

Abstract

Chrysomya megacephala (Fabricius, 1794) has a wide distribution and medical-veterinary relevance, acting as a vector of various pathogens. The control of this insect is predominantly carried out through synthetic insecticides, which have led to resistance selection and environmental impacts. In this context, interest in alternative strategies, such as the use of essential oils, is increasing. The literature indicates the insecticidal potential of Lippia grata (alecrim-do-mato) against insects of medical importance; however, its efficacy against muscoid dipterans, such as C. megacephala, remains little explored. This study evaluated the insecticidal and repellent activity of L. grata essential oil against C. megacephala under laboratory conditions. The essential oil of L. grata was obtained by hydrodistillation and tested at different concentrations. For insecticidal bioassays, 3 µL doses at concentrations of 0,859 g/mL, 0,644 g/mL, 0,429 g/mL, 0,214 g/mL, 0,150 g/mL, 0,128 g/mL, 0,107 g/mL, 0,053 g/mL, and 0,026 g/mL were applied to adults, and 0,859 g/mL, 0,644 g/mL, 0,429 g/mL, 0,214 g/mL, or 0,107 g/mL to third instar larvae (L3). Toxicity was assessed at different time intervals, and lethal concentrations (LC₅₀ and LC₉₀) were determined using Probit analysis. For repellency bioassays, the concentrations used were 0,859 g/mL, 0,429 g/mL, 0,214 g/mL, 0,107 g/mL and 0,053 g/mL, applied (1 mL) on filter paper, with activity evaluated using a specific experimental setup and within a defined period. The repellent concentrations (RC₅₀ and RC₉₀) were also determined by Probit analysis. Carvacrol (51,4%) was identified as the major compound in the oil. Adult mortality was dose-dependent (p<0,001), with total mortality observed at concentrations of 0,859 g/mL, 0,644 g/mL, 0,429 g/mL, 0,214 g/mL and 0,150 g/mL. The LC₅₀ and LC₉₀ values were 0,052 g/mL and 0,211 g/mL, respectively, after 48 hours. In the larvicidal bioassays, the doses of 0,859 g/mL and 0,644 g/mL showed significantly higher effects (p<0,0006) compared to the other concentrations. The LC₅₀ and LC₉₀ values were 0,202 g/mL and 7,42 g/mL, respectively. Color changes in immature stages were observed following treatment, along with high inhibition of adult emergence and deformed adults incompatible with life. In repellency bioassays, the 0.859 g/mL concentration exhibited a significantly superior repellent effect (p<0,05) compared to the others. The RC₅₀ and RC₉₀ values were 0,267 g/mL and 0,984 g/mL, respectively. The growing demand for botanical insecticides highlights L. grata essential oil as a promising alternative. This study demonstrated its high dose-dependent efficacy against C. megacephala, with significant adult and larval mortality and repellency, in addition to drastically inhibiting adult emergence. Its composition rich in Carvacrol and Thymol, acting synergistically, suggests multiple neurotoxic mechanisms of action, including acetylcholinesterase inhibition and modulation of GABAergic and octopaminergic receptors, as well as morphological alterations. These findings reinforce the potential of L. grata oil as a natural and effective solution for the control of this medically important fly species.