Evaluation of encapsulation systems in the efficacy of essential oils of aromatic plants against Tetranychus urticae

The essential oils (EOs) of aromatic plants have shown promise in the control of crop pests whereas their encapsulation in biodegradable and biocompatible nanosystem carriers may increase their bioactivity. In this work, the EOs of three aromatic plants, Mentha pulegium L., Ocimum basilicum L. and Origanum majorana L. encapsulated in yeast cells and β-cyclodextrin (β-CD) were evaluated for their potential in the control of Tetranychus urticae Koch (Acari: Tetranychidae). The chemical profile of each EO was determined using the GC-MS technique. Contact toxicity and repellency bioassays were conducted. In the former case, nymphal mortality was recorded daily for 7 days post treatment and in the latter case, the number of adults on each side of a bean leaf disc which had been previously half-dipped in each emulsion or encapsulated oil recorded 1h, 2h, 4h and 24h after treatment. Finally, their side effects were explored in the case of the predatory mite Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae). The main components of M. pulegium, O. majorana and O. basilicum EO was pulegone (66.5%), terpinen-4-ol (40.6%) and linalool (49.8%), respectively. The results showed that M. pulegium EO caused a 58% mortality rate on nymphs while the encapsulated oil in β-CD and yeast cells showed remarkably increased mortality rates (88% and 90%, respectively). O. basilicum EO caused 37% mortality. However, its encapsulation in β-CD or yeast cells almost doubled its efficacy (76% and 70%, respectively). An increase was also recorded for O. majorana EO (84% vs. 90% and 88%, respectively). Encapsulated EOs in most cases showed an extended period of bioactivity. M. pulegium and O. basilicum caused high repellency activity. Finally, no mortality was recorded in the case of P. persimilis. In conclusion, the EO of O. majorana was highly effective against T. urticae nymphs whereas the encapsulation of M. pulegium or O. basilicum EOs highly increased their repellency.