In vitro study of the efficacy of two essential oils: Rosmarinus officinalis L .and Thymus vulgaris L. on the potato moth, Phthorimaea operculella, Zeller (1873) (Lepidoptera: Gelechiidae) The potato moth is recognized as the most dreadful pest of these strategic crops in stock. This study is part of the search for alternatives to chemical control by using two biopesticides, namely the essential oil of rosemary (Rosmarinus officinalis) and thyme (Thymus vulgaris) obtained by the method of hydrodistillation and by steam distillation (Rdt 0.67%; Rdt 1.53% respectively). An initial work was carried on the study of the life cycle of Phthorimeae operculella under laboratory conditions (temperature 30±2°c; humidity 60% and a photoperiod of 12 h). The results show a relationship between the duration of the stages and the temperature at which they are reared (egg, 3-5 days; (L1) 3-4 days; (L2) 2-3 days; (L3) 3-4 days; (L4) 3-5 days; pupa, 5-7 days; adult, 11-15 days). The in vitro application of both biopesticides showed a real insecticidal action towards the tested individuals with an almost identical efficiency (3.3±0.30 and 3.68±0.13).