Natural repellents based on three botanical species essential oils as an eco-friendly approach against aphids

The aim of this work is to analyze the chemical composition of Cymbopogon citratus, Salvia officinalis and Origanum majorana essential oils (EO) and evaluate their repellent effects on economically significant aphid species. The hydrodistillation yields of the plant's aerial parts were 0.45%, 0.32% and 0.25% for O. majorana, S. officinalis and C. citratus respectively. Chemical analysis by GC-MS identified 87.6%, 100% and 97% of C. citratus, S. officinalis and O. majorana chemical composition respectively. S. officinalis EO was mainly composed of α-thujone (25.7%) and camphor (18.4%), while C. citratus EO major compounds were neral (26.4%) and geranial (30.6%). Finally, O. majorana EO was principally constituted of 4-terpineol (38.7%). Then, the repellency potential of these EO was assessed in vitro on Myzus persicae, Aphis gossypii, Aphis spiraecola and Aphis fabae. In vitro bioassays showed that 2 µL of the three EO were insufficiently repellent on all aphid species during the surveyed period. However, at 120 min, 5 µL EO repellencies were variable from repellent to very repellent depending on the EO and aphid species. Interestingly, 5 µL of O. majorana EO were very repellent for M. persicae and A. fabae after 120 min. Furthermore, in vivo repellency bioassays of 5 µL O. majorana EO were carried out for M. persicae and A. fabae. After 120 min, results showed a statistically higher repellency on M. persicae (repellent) compared to A. fabae (moderately repellent). The in vivo RT50 and RT90 of 5 µL O. majorana EO for M. persicae were 54.68 min and 131.26 min respectively, while A. fabae recorded RT50 of 107.93 min and RT90 of 287.24 min. Both in vitro and in vivo bioassays demonstrated that the tested EO repellencies never decreased over the investigated periods. These results suggest that the studied EO can be used as botanical repellents against these aphid species.