Nectar of the invasive Rhododendron ponticum can have negative impacts on native bee health
Invasive alien plants can provide an abundant nectar source to native pollinators however, this can lead to changes in the pollinator community structure. The nectar of some plant species contains secondary compounds that are usually associated with defence against herbivores. Within native plant communities, the response of pollinators to these often low levels of secondary compounds ranges from positive to negative depending on the species. Rhododendron ponticum subsp. baeticum was introduced from the Iberian Peninsula into Britain and Ireland in the 18th century and mature plants produce hundreds of flowers with sugar rich nectar. This nectar contains high concentrations of diterpenes known as grayanotoxins (R. ponticum nectar contains grayanotoxins I and III) which are known to be toxic to mammals. However, little is known about their potential toxicity to pollinators. In the present study three bee species (honeybee - Apis mellifera, bumblebee - Bombus terrestris and solitary mining bee - Andrena carantonica), which are native to areas invaded by R. ponticum subsp. baeticum, were fed with nectar solutions each containing grayanotoxins I and III at varying concentrations, plus a solution free from grayanotoxins. The survival rate of solitary bees and bumblebees were not affected by the grayanotoxins but individual honeybees were 20 times more likely to die when fed with solutions containing grayanotoxin I. The current experiments suggest that although R. ponticum subsp. baeticum contains high levels of nectar which can be utilised by some pollinator species, others may experience negative impacts as a result of R. ponticum subsp. baeticum invasion.
Sources
Tiedeken EJ, Egan PA, Stevenson PC, Wright GA, Brown MJF, Power EF, Farrell I, Matthews SM & Stout JC (2015) Nectar chemistry modulates the impact of an invasive plant on native pollinators. Functional Ecology. DOI: 10.1111/1365-2435.12588.