Thymol: an alternative treatment for control of Nosema ceranae?

In a first series of trials the natural compounds thymol, resveratrol, vetiver essential oil and lysozyme were assessed for potential use in control of Nosema ceranae infection ofhoney bees. None of the substances showed an increased bee mortality or decreased dietary preference. Adult worker bees from a nosema-free apiary were individually infected with 1 l of sucrose syrup containing 18000 N. ceranae spores, placed in cages and fed with candies cpntaining the screened substances. Infection levels were monitored over 25 days, by removal and dissection of 2 live bees per cage. On day 25 post-infectionbees fed with candies containing thymol and resveratrol had significantly lower infection rates, and bees supplied with resveratrol candy also lived significantly longer.In a second set of trials the two most promising active ingredients, thymol (100 ppm) and resveratrol (10 ppm), were supplied to artificially infected bees in candy or in syrup, withthe same procedure used in the first trials. On day 25 post-infection bees fed with thymol syrup had significantly lower levels of infection compared to control bees. Bees fed withthymol and resveratrol syrup lived significantly longer than bees fed with control syrup. Following the promising results, field tests were performed by feeding naturally nosema infected hives with syrup containing thymol during two consecutive springs. In the first year no significant differences in infection levels were observed, while in the second year the hives treated with thymol had a significantly greater decrease in infection comparedto the control group