Aphicidal and biochemical effects of emulsifiable concentrate and nanoemulsion of two selected essential oils against black bean aphid, Aphis fabae (Scop.)

Background and objectives Aphids are cosmopolitan pests that feed on a wide range of host plants from different botanical families. Aphids have developed resistance to several groups of synthetic insecticides. Because of their antimicrobial, antiviral, and insect-repellent properties, essential oils extracted from medicinal plants are excellent sources of various bioactive compounds. Formulation of essential oils as emulsifiable concentrate (EC) and nanoemulsion (NE) could help to enhance their bioavailability. Materials and methods The insecticidal activity of essential oils derived from two medicinal plants, namely, Proserpinaca palustris L. and Terminalia chebula Retz., was evaluated against black bean aphid, Aphis fabae (Scop.), under laboratory and semifield conditions. The essential oils from both plants were synthesized as EC and NE formulations to enhance their insecticidal efficacy. The stability of ECs and droplet size of NEs were assessed. The toxicity of ECs in comparison with NEs was evaluated against A. fabae adults. Moreover, the biochemical efficacy of the two essential oils on the activity of acetylcholinesterase and glutathione S-transferase enzymes of A. fabae was studied. Results and conclusion In laboratory bioassay, both ECs and NEs of selected oils displayed significant toxicity in controlling A. fabae, with lethal concentration values (LC50) for P. palustris EC and NE being 0.59 and 0.50%, respectively. Moreover, LC50 for T. chebula EC and NE was 0.65 and 0.78%, respectively. The bulk essential oils showed less toxic activity against A. fabae adults, with LC50 of 0.68 and 1.16% for P. palustris and T. chebula bulk forms, respectively. Under semifield conditions, EC of P. palustris and T. chebula at LC90 and LC90x3 exhibited greatly lethal effects for aphid adults compared with NE formulations. Both formulations (ECs and NEs) significantly increased the reduction percent of acetylcholinesterase and glutathione S-transferase enzymes of the treated aphid adults. Our results suggest that EC and NE formulations from P. palustris and T. chebula enhanced the insecticidal toxicity of the selected oils and could be used to effectively control A. fabae adults.