Non-native plant species impact on native pollinators such as bumblebees, which are tricked by showy foliage, writes Anthony King.
Aliens may be interfering with Irish bees and other insects, but not the kind from outer space. These aliens are invasive, non-native plants now common in many Irish forests and bogs, and their arrival can have unexpected effects.
"We are looking at how alien plants affect the pollination of native plants and also at how they affect native pollinators," says Dr Jane Stout of the botany department in Trinity College Dublin, who studies the effects of non-native plants on biodiversity.
There is global concern about the loss of bumblebees and other pollinating insects given they are important for wild flower and crop pollination. "If there is a decline in pollinators, there could be a decline in agricultural crop yields," says Stout.
Exotic plant species could be having either detrimental effects or positive effects on bumblebees, she suggests. "We don't know what the impacts are yet. It's a work in progress, but it is generally accepted that alien plants are a huge threat to native biodiversity."
Alien plants may have positive impacts by providing floral resources to bees by way of nectar and pollen, important since the availability of this food has declined due to agricultural intensification.
On the other hand, they might have a negative impact on bees. They might not be any good as a floral resource because they flower at the wrong time of year or the nectar or pollen isn't accessible to our native bee species.
"Rhododendron, for example, provides plenty of food in April and May, but nothing after that," says Dr Mark Brown, a bee expert in Trinity's zoology department.
Queen bumblebees searching for good nest sites in April might be attracted to an area where rhododendron is common, but the area may then be bereft of food by July.
Unfortunately, this colourful plant tends to dominate landscapes by poisoning soil and keeping native plant species out. And with invasive aliens, it's not just the change in the type of flowers but a change in the vegetation and structure of the ecosystem that affects bees.
Two PhD projects in Trinity's Botany Department are looking at pollinators and exotic plants. Caroline Nienhuis is investigating whether alien plants are important as a forage resource for bumblebees.
She is assessing the quantity and quality of nectar and pollen provided by these plants. It is known that the protein content of pollen varies and some pollen is more suitable for bees than others.
Anke Dietzsch is looking at the impact of alien plants on native plant-pollinator interactions using rhododendron as the model alien species. So far, the picture appears complicated, with rhododendron having good and bad effects on different types of plants and insects.
Stout believes her team has much to contribute to bee conservation. "The more we find out about bees' food resources and what is happening in plant communities, the more we can contribute to the management of bees," she says.
"Before, people were looking at alien plants and saying they are having an effect on grazers, native plants and ecology," says Stout. "It's only relatively recently people have started looking at impacts on pollinators."
Green aliens abroad in the Irish countryside include buddleia, fuchsia, Himalayan balsam and Japanese knotweed. The Trinity botanists are looking at what impact controlling such species would have on bumblebee foraging and ecology.
"In the short-term, the removal of aliens leaves a blank space that can become invaded by other aliens and might take away a big flower resource for bees," says Stout.
She adds, however, that the effect would likely be beneficial in the long-term if a management plan is put in place to get native plants to return.
People can help bees by planting appropriate plants that provide pollen and nectar throughout the year and, if possible, by not mowing every piece of lawn, says Dr Brown. Red clover, foxglove, and honeysuckle are listed by the Bumblebee Conservation Trust in the UK as plants favoured by bumblebees.