Phytochemical composition and larvicidal activities of Artemisia herba-alba, Thymus numidicus and Citrus limon peel essential oils on the pine processionary moth

Abstract

The pine processionary moth (PPM) (Thaumetopoea pityocampa, Denis and Schiffer-Müller 1775, Lepidoptera: Notodontidae) is one of the most dangerous pests of pine and cedar in the Mediterranean forest area. During feeding on fresh needles, larvae participate in weakening trees ecological quality, making them more vulnerable to environmental stress. Large infestations can lead to significant defoliations, and even to the decline of the entire forest. In the present study, a variety of three essential oils (EOs) (Artemisia herba-alba, Thymus numidicus, and Citrus limon), belonging to diverse botanical families, have been evaluated on the 2nd, 3rd and 4th moth larval stages. The toxicological effect was estimated under controlled conditions at 24, 48, 72, and 96 h. Results showed that EOs yields ranged between 2.17 % for T. numidicus, 1.32 % for A. herba-alba, and 1.02 % for C. limon. The major chemical components identified using GC-MS protocol were thymol (27.68 %) and carvacrol (16.37 %) for T. numidicus, camphor (28.56 %) and β-thujone (20.60 %) for A. herba-alba, and limonene (51.28 %) and o-cymene (27.99 %) for C. limon. Mortality gradually increased with concentration and prolonged exposure duration. The highest mortality rates were observed in the 2nd and 3rd larval instars with T. numidicus (95 % and 62 %) and A. herba-alba (70 % and 72.5 %) EOs, compared to C. limon EO, which showed a moderate effect (50 % and 42.5 %) after 96 h at the highest concentration (1 %). This study pointed out that T. numidicus EO, rich in phenolic compounds (thymol and carvacrol), exhibited higher insecticidal potency against PPM larvae. Further exploration of its impact on PPM and other lepidopteran pests should include field trials and the development of suitable formulations that ensure stability and prolonged activity under natural conditions.