Ornamental plants on sale to the public are a significant source of pesticide residues with implications for the health of pollinating insects

Abstract

Garden centres frequently market nectar-and pollen-rich ornamental plants as "pollinator-friendly", however these plants are often treated with pesticides during their production. There is little information on the nature of pesticide residues present at the point of purchase and whether these plants may actually pose a threat to, rather than benefit, the health of pollinating insects. Using mass spectrometry analyses, this study screened leaves from 29 different 'bee-friendly' plants for 8 insecticides and 16 fungicides commonly used in ornamental production. Only two plants (a Narcissus and a Salvia variety) did not contain any pesticide and 23 plants contained more than one pesticide, with some species containing mixtures of 7 (Ageratum houstonianum) and 10 (Erica carnea) different agrochemicals. Neonicotinoid insecticides were detected in more than 70% of the analysed plants, and chlorpyrifos and pyrethroid insecticides were found in 10% and 7% of plants respectively. Boscalid, spiroxamine and DMI-fungicides were detected in 40% of plants. Pollen samples collected from 18 different plants contained a total of 13 different pesticides. Systemic compounds were detected in pollen samples at similar concentrations to those in leaves. However, some contact (chlorpyrifos) and localised penetrant pesticides (iprodione, pyroclastrobin and prochloraz) were also detected in pollen, likely arising from direct contamination during spraying. The neonicotinoids thiamethoxam, clothianidin and imidacloprid and the organophosphate chlorpyrifos were present in pollen at concentrations between 6.9 and 81 ng/g and at levels that overlap with those known to cause harm to bees. The net effect on pollinators of buying plants that are a rich source of forage for them but simultaneously risk exposing them to a cocktail of pesticides is not clear. Gardeners who wish to gain the benefits without the risks should seek uncontaminated plants by growing their own from seed, plant-swapping or by buying plants from an organic nursery. Capsule summarising main findings (requested by journal)Many plants that might be bought by gardeners as "bee-friendly" contain multiple pesticides, including neonicotinoid insecticides, at levels likely to be harmful to bees.Introduction.

Quantifying the impact of pesticides on learning and memory in bees

“…Chronic exposure had a stronger effect than acute exposure for the memory dataset, potentially because bodily pesticide residues from acute doses may be more likely to have been metabolized before the memory trial than chronic doses, but both chronic and acute doses significantly impaired both learning and memory. Chronic pesticide exposure is increasingly likely to occur in the field as water‐soluble systemic pesticides have been found to occur in wild flowers on field margins (Botias et al., ), and in flowers sold in garden centres (Lentola et al., ), while pesticide products are freely available for gardeners to purchase, and bees preferentially feed on sucrose solutions that have been treated with pesticides (Kessler et al., ). Our results draw together a body of evidence that in combination suggests the rising prevalence of pesticides in the environment (Mitchell et al., ) is increasingly likely to influence the cognitive abilities of bees.…”

Larval exposure to field-realistic concentrations of clothianidin has no effect on development rate, over-winter survival or adult metabolic rate in a solitary bee, Osmia bicornis

“…Until recently, the majority of studies and regulatory tests have focussed on the effects of short term, acute exposure in adult bees, with a bias towards commercially reared social species such as honeybees and bumblebees. Given that neonicotinoid pesticides have been detected not only in the pollen and nectar of treated crops but also of wild flowers growing in the margins of fields, as well in ornamental garden plants (Botías et al, 2015; Mogren & Lundgren, 2016; David et al, 2016; Long & Krupke, 2016; Lentola et al, 2017) a host of bee species are likely to encounter these chemicals when foraging (Hladik, Vandever & Smalling, 2016; Botías et al, 2017), and yet we still know relatively little about the sensitivity of wild bees to neonicotinoids.…”

Effects of neonicotinoid insecticide exposure and monofloral diet on nest-founding bumblebee queens

“…For the imidacloprid-treated queens (hereafter, 'IMD'), the 50% (w/v) sucrose solution was treated with imidacloprid (Pestanal analytical standard, Sigma-Aldrich) at a level of 5 ppb. Imidacloprid has been detected at this level in wildflowers near agricultural fields in the southern US (earlyseason [51]) and southeastern UK (in early summer [20]), and in worker bumblebee pollen loads in urban areas in the UK [21], and thus 5 ppb is a field-realistic exposure level for experimental analyses, including with queens. A summary of studies on imidacloprid exposure is provided in the electronic supplementary material.…”