Review: Maistrello et al. (2008). Apidologie, 39: 436-445

Written: September 5, 2008

Posted: 09/05/08

Word count: 629

Question: Can thymol kill Nosema?

Answer: Yes, but it’s not administered to the bees in the way you might think.

There has been a lot of discussion and study on Nosema disease lately. Once considered an afterthought for treatment and overall colony health, nosema has resurged to the forefront of beekeeping management ever since it was discovered that a new species, Nosema ceranae, is now infecting our bees and, in fact, supplanting the original nosema species, N. apis. Studies out of Europe blame this internal gut parasite (a microsproidian) for massive losses of colonies on that continent.

Spores of nosema are spread from infected adults to uninfected nestmates, usually through defecation inside the hive. This is particularly common during the colder months of the year, when older bees are cooped up inside without ample opportunity to fly and void themselves. The standard treatment recommendation, when seeing defecation inside the hive and swollen abdomens of listless bees, is to feed the antibiotic fumagilin dissolved in sugar syrup (which, if you’ve ever tried, is surprisingly easier said than done), which has been proven quite effective at clearing up nosema infections. But, as with all single-chemical control methods, the need is great for alternative means of control, both to reduce the likelihood of resistance of nosema to fumagilin as well as to increase the options for beekeepers.

A research team from Italy recently screened some natural compounds for their potential control of nosema. First, they tested vetiver essential oil, which has been shown to kill the gut symbionts of termites (the flagellates that digest the cellulose in wood that the termites eat). Second, they tested lysozyme, a standard enzyme in many animals that kills bacteria and viruses. Third, they tested resveratrol, a toxin produced by certain plants that is known for its anti-cancer properties and has been shown to kill other microsporidian species in petrie dishes. Finally, they tested a second essential oil—one well-known to beekeepers—thymol. Used in several products to help control varroa mites, they wished to determine if the biopesticide has any potential use for nosema control as well.

Unlike feeding these natural compounds through sugar syrup like fumagilin, the research team fed infected bees by providing them with “laced” sugar candy (a mixture of 85% powdered sugar, 10% sterilized honey, and 5% water). This is a common means of supplementally feeding honey bee colonies during the colder months of the year, and is therefore a more efficient means of targeting infected bees right at the time that they are most contagious. Tests in the lab suggest that mortality didn’t differ among bees feeding on candy with vetiver, lysozyme, resveratrol, or thymol compared to controls, suggesting that the chemicals were themselves not toxic to the bees at the levels tested. More importantly, however, is that thymol (at 0.12 mg/g of candy) and resveratrol (at 0.001mg/g of candy) both significantly lowered the nosema infection rates of the experimental bees.

These are quite encouraging results for several reasons. First, it introduces another possible delivery mechanism for products to increase colony health. Second, it suggests at least two possible alternatives to fumagilin for nosema control, which may be very helpful particularly if nosema develops resistance. So while the current thymol products on the market for varroa control may not be “two-for-one” products for nosema (since the bees do not ingest the thymol), there is hope that this essential oil may help colony health in other ways as well.

Reference

Maistrello, L. M. Lodesani, C. Costa, F. Leonardi, G. Marani, M. Caldon, F. Mutinelli, and A. Granato. (2008). Screening of natural compounds for the control of nosema disease in honeybees (Apis mellifera). Apidologie, 39: 436-445.