Chemical Profile of Essential Oils of Selected Lamiaceae Plants and In Vitro Activity for Varroosis Control in Honeybees (Apis mellifera)

Simple Summary Varroa destructor acariasis is currently the main threat to the health and survival of honeybee colonies. Chemicals are often used to control this parasitosis. However, overuse and misuse over the years has allowed the mite to acquire resistance to synthetic active ingredients. In this scenario, it is vital to search for alternative therapeutic solutions. Essential oils (EOs) are a promising therapeutic choice, as they have a complex chemical composition, making them unlikely to be prone to the development of resistance. In addition, they are easily degraded in the environment and have a low toxicity for humans, characteristics that make them particularly attractive. In this research study, four EOs from the Lamiaceae family, isolated from botanical species native to the Calabria region, Southern Italy, were tested in contact toxicity tests against V. destructor. Origanum vulgare subsp. viridulum, Thymus capitatus and Thymus longicaulis, used at 2 mg/mL, were found to have a high level of efficacy, neutralizing (dead + inactivated) 94%, 92% and 94% of parasites, respectively. These EOs could be chosen and tested in subsequent in vivo studies.Abstract The most significant ectoparasitic mite of honeybees, Varroa destructor, has a detrimental effect on bee health and honey output. The principal strategy used by the control programs is the application of synthetic acaricides. All of this has resulted in drug resistance, which is now a major worry for beekeeping. As a result, research on alternate products and techniques for mite management is now required. The aim of this study was to determine whether essential oils (EOs) extracted from botanical species of Lamiacae, typical of the Calabria region of Southern Italy, could reduce the population of the mite V. destructor. Among the best-known genera of the Lamiaceae family are oregano, rosemary and thyme, whose EOs were employed in this study. By steam distillation, the EOs were extracted from Origanum vulgare subsp. viridulum (Martrin-Donos) Nyman, Thymus capitatus Hoffmanns. and Link, Thymus longicaulis C.Presl and Salvia rosmarinus Schleid. plant species harvested directly on the Calabrian territory in their balsamic time. Each EO went to the test in vitro (contact toxicity) against V. destructor. Fifty adult female mites, five for each EO and the positive and negative control, were used in each experimental replicate. The positive controls comprised five individuals treated to Amitraz dilute in acetone, and the negative controls included five individuals exposed to acetone alone. To create the working solution to be tested (50 mu L/tube), the EOs were diluted (0.5 mg/mL, 1 mg/mL, 2 mg/mL and 4 mg/mL) in HPLC-grade acetone. After 1 h of exposure, mite mortality was manually assessed. Origanum vulgare subsp. viridulum, Thymus capitatus and Thymus longicaulis were the EOs with the highest levels of efficiency at 2 mg/mL, neutralizing (dead + inactivated), 94%, 92% and 94% of parasites, respectively. Salvia rosmarinus EO gave a lower efficacy, resulting in a percentage of 38%. Interestingly, no adverse effects were highlighted in toxicity tests on honeybees. These results show that these OEs of the Lamiaceae family have antiparasitic action on V. destructor. Therefore, they could be used, individually or combined, to exploit the synergistic effect for a more sustainable control of this parasite mite in honeybee farms.