Honey bees (Apis mellifera L.) at ornamental plant nurseries collect very little pollen from ornamental plants

Pollen is the main source of protein, fats, and many micronutrients for honey bees. It has the potential to be a major route of exposure to pesticides. Environmental organizations and consumers have been concerned about the use of systemic insecticides on ornamental plants as a possible hazard to honey bees. We kept honey bee colonies at two major commercial ornamental plant nurseries in 2018, and trapped pollen from returning foragers weekly, weighing the pollen collected. Subsamples of the weekly pollen were analyzed by a palynologist, identifying most pollen grains to genus. Using the proportion of pollen types in the subsample and the weight of pollen collected in each weekly bulk sample, we estimated the proportion of pollen from different plant sources. Corn (Zea) was the largest source of pollen at one nursery (34% of the seasonal total) and the second largest source at the other nursery (22%). Other major pollen sources at the first nursery were rose (Rosa, including wild species as well as cultivated species), poison ivy (Toxicodendron), bur clovers (Medicago, including alfalfa), other clovers (Trifolium), and plantain (Plantago). At the other nursery, in addition to corn, major pollen sources were crown vetch (Securigera), impatiens (Impatiens, including wild species as well as cultivated species), ragweed (Ambrosia, or possibly Xanthium), buckwheat (Fagopyrum), poison ivy, and hops (Humulus). Thus, even at an ornamental plant nursery, most pollen came from crops or wild plants rather than ornamental plants.