Tracking Pesticide Residues to a Plant Genus Using Palynology in Pollen Trapped from Honey Bees (Hymenoptera: Apidae) at Ornamental Plant Nurseries

The authors collected pollen pellets from forager honey bees returning to hives situated at three Connecticut ornamental wholesale plant nurseries in 2015.  Seventeen insecticides and acaricides (including their metabolites), 16 fungicides and 9 herbicides were detected in the collected pollen.

For each pesticide detected in a sample, Pollen Hazard Quotients and estimated daily LD50 consumption for nurse bees from the pollen were calculated following the method of Stoner and Eitzer (2013). Pollen Hazard Quotients were summed across pesticides contained in a single sample to get an overall Pollen Hazard Quotient for the sample, based on an assumption of additive toxicity.

The major pesticides adding to the Pollen Hazard Quotients were the nitroguanidine neonicotinoids (imidacloprid, thiamethoxam, and its metabolite clothianidin) followed by the organophosphate acephate and its metabolite methamidophos.

The rest of the insecticides and acaricides had relatively little effect on Pollen Hazard Quotients, except for carbaryl, which was detected in only two samples at one nursery.

Pollen from the plant genus Spiraea grown at one nursery contained extraordinarily high concentrations of the systemics thiamethoxam and clothianidin, and also high concentrations of acephate and its metabolite methamidophos. Further direct experimentation with Spiraea could determine why these insecticides were found in such high concentrations in this plant genus, when thiamethoxam and acephate were both used on a wide range of plants at the nursery. This study is the first to trace highly toxic pollen collected by honey bees to a single plant genus.

Data are not directly comparable to those of Friends of the Earth (Brown et al. 2014, Kegley et al. 2016) or Lentola et al. (2017), because this study’s samples of trapped pollen did not come directly from nursery plants, but would be expected to contain a mix of species from the wide geographical range covered by honey bee foragers. This study adds to the pool of data showing that pesticide residues in the pollen pool are highly heterogeneous in time and by plant source.

Stoner, Kimberly A ., Cowles, Richard S., Nurse, A., and Eitzer, Brian D
Environmental Entomology
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