The need for alternatives to synthetic pesticides is a priority today, especially when these pesticides are directed against aphids, one of the more challenging pests facing modern agriculture. Essential oils may be one of these alternatives. We assayed the insecticidal potential of essential oils from Thymus vulgaris, Rosmarinus officinalis var. 'prostratus' and Lavandula dentata. Essential oil extraction was carried out by hydrodistillation in a Clevenger-type apparatus for 3 h and their respective composition was elucidated by gas chromatography-mass spectrometry. The essential oil fraction from T. vulgaris contained 81.20% monoterpenoids and 12.85% sesquiterpenoids; R. officinalis var. 'prostratus' contained 91.98% monoterpenoids and 1.93% sesquiterpenoids, while L. dentata contained 69.60% monoterpenoids and 8.05% sesquiterpenoids. The major components found were 1,8-cineole (18.11%), camphor (11.18) and borneol (10.32%) in T. vulgaris; α-pinene (18.72%), verbenone (13.42%) and 1,8-cineole (10.32%) in R. officinalis; and 1,8-cineole (34.65%), camphor (7.58%) and β-pinene (6.39%) in L. dentata. The insecticidal activity of the essential oils was evaluated by contact toxicity bioassays against the bird cherry oat aphid, Rhopalosiphum padi L. We observed a mortality rate of 78.3% ± 23.9 at 15 μL/mL with T. vulgaris, 54.7% ± 25.8 with L. dentata (although at a lower concentration, 10 μL/mL), and 56.7% ± 25.6 at 15 μL/mL with R. officinalis. Our results suggest that thyme essential oil may be particularly promising for integrated aphid management provided that specific conditions of use and dosages are observed.
Keywords: Rhopalosiphum padi; biopesticide; integrated pest control; natural insecticide; sustainable agriculture.