Ornamental plants as a source of pesticide exposure for pollinators

Ornamental plants for sale to the public were the focus of a recent study by scientists from Italy and the UK.  The goal was to determine whether pollinator-attracting flowering plants, from local garden centres in East Sussex, England, were a source of toxic pesticides with potential to contaminate pollinators (e.g. bees, hover flies, butterflies, etc.).

Leaf samples were collected from 29 different species/varieties, and pollen samples were collected from 18 species/varieties.  Pesticides chosen for analyses were those most widely used in the UK, including 5 neonicotinoid insecticides, 2 pyrethroid insecticides, 1 organophosphate insecticide, and 16 fungicides.

Plants from each supplier contained pesticide residues.  Of the 29 different species/varieties analyzed, only 2 (a daffodil and a salvia) did not contain residues of any of the pesticides being tested for on leaves, whereas 23 contained more than one pesticide, 2 of which contained a mixture of 7 (an ageratum) and 10 (a heather) different insecticides and fungicides.  This indicates that the leaves of ornamental plants can often be contaminated with mixtures of insecticides and fungicides.  Neonicotinoids were detected in more than 70% of the plants analyzed; the organophosphate was detected in 10%; pyrethroids in 7%; and fungicides in 38%.

A total of 13 different pesticides were found in pollen samples.  When examining individual plants, there was a highly significant correlation between systemic pesticide concentrations detected in leaves and those detected in pollen.  This suggests that systemic pesticides are easily transported to the pollen.  In addition, some contact pesticides and localized penetrant pesticides were also detected in pollen, likely due to pesticide spraying during flowering.

Many ornamental flowering plants are a rich source of pollen and nectar in urban environments, and pollinators are often attracted to these plants.  Many gardeners purchase plants with the intention of providing wildlife habitat, including providing forage for pollinators.  Pollinators foraging at the flowers analyzed here would likely be exposed to a mixture of chemicals, and numerous studies report pesticides as having additive, or even synergistic, effects when used in combination with other pesticides.

Many ornamental plants are bought and planted in spring, which may expose bumblebees to pesticides at a critical period during early development of bumblebee colonies.  The safest option for anyone wishing to help pollinator populations would be to buy plants from organic nurseries or grow plants from seed.  Hopefully, growers will begin to add pesticide exposure information to plant labels, allowing consumers to make an informed choice.

LINK to Lentola et al.'s 2017 article in Environmental Pollution.