Essential oils of Lavandula angustifolia and Thymus vulgaris as biocontrol agents: managing Dactylopius opuntiae infestation and associated bacterial infections

Abstract

Dactylopius opuntiae, the invasive cactus cochineal, is a major pest threatening Opuntia ficus-indica cultivation, especially in arid regions. This study assesses the insecticidal and antibacterial properties of essential oils (EOs) from Lavandula angustifolia (lavender) and Thymus vulgaris (thyme) as eco-friendly biocontrol agents. Laboratory (in vitro) and greenhouse (in vivo) tests were performed using emulsified EOs at 1%, 5%, and 10% concentrations. In vitro tests showed that lavender EO caused 95.0 ± 3.0% mortality in nymphs and adult females of D. opuntiae at 10% after 8 days, with an LT₅₀ of 3.0 days. Thyme EO was slightly less effective (90.0 ± 3.5%, LT₅₀ = 3.5 days). Greenhouse experiments indicated reduced but significant efficacy (85.5 ± 4.0% and 80.0 ± 4.5% mortality for lavender and thyme EOs at 10%, respectively). Disk diffusion and broth microdilution tests against Proteus penneri showed that thyme EO had stronger antibacterial activity (MIC = 0.625%, MBC = 1.25%) than lavender EO (MIC = 1.25%, MBC = 2.5%), both with bactericidal effects. These findings demonstrate the dual insecticidal and antibacterial potential of lavender and thyme EOs, supporting their inclusion in Integrated Pest Management (IPM) programs. Further research is needed to evaluate their field persistence, effects on non-target organisms, and formulation stability for sustainable cactus pest control.