Nineteen essential oils, obtained by hydrodistillation from aromatic and medicinal plants of Moroccan origin, were tested for their insecticidal effects on Hessian fly (Cecidomyiidae) adults and eggs. This insect is the major pest of wheat in Morocco. Most of the aromatic plants belong to the family Labiatae. The species Mentha pulegium, Origanum compactum, and Origanum majorana were the most toxic to adults; Ammi-visnaga, Pistacia lentiscus, O. compactum, and M. pulegium were more efficient on eggs.