Chemical characterization and acaricidal activity of Thymus satureioides C. & B. and Origanum elongatum E. & M. (Lamiaceae) essential oils against Varroa destructor Anderson & Trueman (Acari: Varroidae)

Thymus satureioides and Origanum elongatum, endemic, aromatic and sources of honey in Morocco, are rich in essential oils (EOs). In Southwest, Varroa destructor affects less bee colonies foraging in thyme (Thymus satureioides) formations. The aim of this study was (i) to determine the composition of T. satureioides and O. elongatum EOs in relation to origins and phenological stages and (ii) to investigate the acaricidal activity against Varroa destructor. Essential oils obtained showed differences in the chemical composition according to plant species but did not vary drastically with the vegetative stage of growth and origins. The main constituents found in T. satureioides EOs were borneol (20.07%-48.23%) and α-terpineol (5.12%-18.16%), smaller amounts of camphen (5.10%-14.44%) and α-pinene (2.43%-7.63%), whereas thymol (0.14%-8.64%) or carvacrol (0.88%-15.23%). O. elongatum EOs contained carvacrol (67.34%-81.72%), γ-terpinene (3.29%-10.75%), para-cymene (3.62%-7.81%) and thymol (1.79%-9.17%). The apiary tests revealed a variable efficacy from 50 to 94% depending on the composition of essential oils. EOs with carvacrol as major compound produced a better effect than other EOs with dominant borneol. However, the blend containing high levels of carvacrol (55.35%) and borneol (20.60%) exhibited much higher activity than all treatments. A synergistic effect between the compounds of T. satureioides and O. elongatum EOs was highlighted.