Chemical composition and larvicidal activities in vitro and in vivo of essential oils of Thymus vulgaris (L) and Lavandula angustifolia (Mill) against pine processionary moth Thaumetopoea pityocampa Den. & Schiff. in Ain Defla (Algeria)

Abstract

Biological tests with Thymus vulgaris against both third and fifth instar larvae of Thaumetopoea pityocampa showed positive correlation between the used doses and mortality after 24 h of application. Treatment against third instars larvae with doses 0.005–0.04 ml L−1 gave 40.97–100% mortalities in vitro condition, and treatment with doses 0.1–0.5 ml L−1 gave 53.85 and 100% mortalities in vivo condition. In addition, similar effect of this natural insecticide is observed against fifth instars larvae with mortality rate varying between 36.11 and 100% at doses of 0.02–0.1 ml in vitro and between 33.96 and 100% mortality with doses of 0.3–1.2 ml in vivo. Bioassay with Lavandula angustifolia against third instar larvae in vitro condition showed between 29.86 and 100% mortality rate, but with high doses between 0.01 and 0.05 ml L−1 compared to T. vulgaris. Furthermore, the mortality recorded in vivo is 73.35% with dose of 1 ml L−1. Whereas the essential oil of L. angustifolia is the least toxic against fifth instar larvae of Thaumetopoea pityocampa with 37.08% at a dose of 1.5 ml L−1 in vivo and 65.97% mortality at a dose of 0.12 ml L−1 in vitro. Histologically, the effect of these essential oils has resulted in a necrosis and degeneration of the intestinal cells, as well as a general destruction of the hair and skin of treated larvae compared to untreated caterpillars. In accordance with these results, it would be possible to use essential oil of T. vulgaris as an effective biological alternative against the larvae of T. pityocampa. The chemical analyses obtained by GC–MS of T. vulgaris essential oil enabled us to identify 35 chemical compounds of which Carvacrol (71%) is the most dominant, whereas for L. angustifolia there are 36 chemical compounds of which we have identified two dominant chemical compounds, Lynalol (37%) and Linalool acetate (25%).