The terpenes of leaves, pollen, and nectar of thyme (Thymus vulgaris) inhibit growth of bee disease-associated microbes

Abstract

Honey bees are highly prone to infectious diseases, causing colony losses in the worst case. However, they combat diseases through a combination of their innate immune system and social defence behaviours like foraging for health-enhancing plant products (e.g. nectar, pollen and resin). Plant secondary metabolites are not only highly active against bacteria and fungi, they might even enhance selective foraging and feeding decisions in the colony. Here, we tested six major plant terpenes and their corresponding acetates, characterizing six natural Thymus vulgaris chemotypes, for their antimicrobial activity on bacteria associated with European foulbrood. Comparison of the inhibitory activity revealed the highest activity for carvacrol and thymol whereas the acetates mostly did not inhibit bacterial growth. All terpenes and acetates are present in the nectar and pollen of thyme, with pollen containing concentrations higher by several orders of magnitude. The physiological response was tested on forager and freshly emerged bees by means of antennal electroantennography. Both responded much stronger to geraniol and trans-sabinene hydrate compared to carvacrol and thymol. In conclusion, bee-forageable thyme product terpenes (mainly from pollen) yield effective antibiotic activity by reducing the growth of bee disease-associated bacteria and can be detected with different response levels by the honey bees’ antennae. This is a further step forward in understanding the complex pathogen-pollinator-plant network.

Honeybee keeping constraints and future prospects

“…The bee forage able thyme product terpenes (mainly from pollen) were an antibiotic that reduces the growth of bee disease-associated with bacteria effectively. This is a further step forward in understanding the complex pathogenpollinator-plant network (Wiese et al, 2018).…”

Inhibitory Effect of Essential Oils From Some Lauraceae Species on the Growth of Penicilium Commune

“…Their antimicrobial activity also depends on their chemical composition (Omonijo et al, 2018). The most effective components of essential oils are predominantly terpenes, terpenoids and phenolic substances (Wiese et al, 2018;Olmedo et al, 2018;Pichersky a Raguso, 2018). Based on the above we evaluated the chemical composition of tested EOs by the GC-MS analysis.…”

Pathogenesis, Epidemiology and Variants of Melissococcus plutonius (Ex White), the Causal Agent of European Foulbrood

“…Tea tree oil nanoparticles (Santos et al, 2014), Malva sylvestris oil (Cecotti et al, 2016), aqueous and ethanolic extracts of Cinnamomum spp. and Persian salvadora (Hashish et al, 2016), macelignan and corosolic acid (Kim et al, 2018), terpenes of Thymus vulgaris (Wiese et al, 2018), among others, have been shown to have significant antibacterial effects against M. plutonius. The use of extracts and essential oils for integrated EFB treatment is promising and stimulates the search for other bioactive plant phytochemicals with bactericidal capacity and low toxicity for bees.…”