Microemulsion of essential oil of Citrus aurantium var. dulcis for control of Aleurocanthus woglumi and evaluation of selectivity against Aschersonia aleyrodis and Ceraeochrysa cornuta
Joseane de Jesus Oliveira, Eliana Maria dos Passos, Suely Moraes Alves, Víctor Hugo Vitorino Sarmento, Thiago Rodrigues Bjerk, Juliana Cordeiro Cardoso, Cristina Blanco-Llamero, Eliana B. Souto, Patrícia Severino, Marcelo da Costa Mendonça
Abstract
The aim of this study was to develop a microemulsion from the essential oil of Citrus aurantium var. dulcis (EOCA) as an alternative to synthetic pesticides, and to evaluate its efficacy against Aleurocanthus woglumi and selectivity towards the natural enemies Aschersonia aleyrodis and Ceraeochrysa cornuta. Chemical composition of the essential oil determined by gas chromatography coupled with mass spectrometry revealed limonene, myrcene, linalool and α-pinene as major components. The microemulsion was prepared using a ternary diagram illustrating the composition of water, essential oil, surfactant (procetyl AWS) and co-surfactant (ethanol). Selected microemulsions were characterized by polarized light microscopy, revealing to be isotropic with a Newtonian behaviour when measuring the shear stress against shear rate. The mean droplet size of microemulsions ranged from 53.69 nm to 2.22 μm. The insecticidal activity was evaluated by assessing three application routes, namely, contact, systemic and translaminar. Selectivity of microemulsions was determined by the percentage of growth inhibition (PGI) of fungi on A. aleyrodis and by contact on eggs and larvae of C. cornuta. The oil (LC50 = 36.07 mg/mL) in its pure form had a lower insecticidal effect on A. woglumi than the microemulsions (LC50 = 18.65 mg/mL). The microemulsions showed systemic insecticidal activity with approximately 90% mortality at 72 h (LC90 = 55.50 mg/mL). On A. aleyrodis, the microemulsion interfered with biomass production, which was concentration dependent. At a concentration of 15.68 mg/mL, a 91% inhibition of biomass production were observed. In the selectivity experiments against C. cornuta, the microemulsions were selective for eggs and larvae, and did not interfere with its predatory capacity.