Bees are essential to our food supply. As they travel from plant to plant collecting pollen for honey, they fertilize a great number of our commercial crops. It's no overstatement to say that without our friends the bees, we'd be in serious trouble. A study at Purdue University now suggests that bees collect the vast majority of their pollen from plants other than crops, even in areas dominated by corn and soybeans, and that this pollen is often contaminated with a number of agricultural and urban pesticides throughout the growing season.
When it comes to agriculture, honeybees do a lot of the hard work for us. According to the American Beekeeping Federation (ABF), "crop yield and quality would be greatly reduced without honeybee pollination." In addition to cereal crops, blueberries and cherries, they say, are 90% reliant on bees for fertilization, while the almond crop "depends entirely on the honeybee for pollination at bloom time."
To get a close look at the process, entomologists Christian Krupke and Elizabeth Long collected pollen from Indiana hives at three sites throughout a 16-week period to learn which pollen sources bees use throughout the season and whether they are contaminated with pesticides. Their pollen samples represented around 30 plant families and were found to contain residues from nine types of pesticide. These included neonicotinoids, a common pesticide, which is chemically related to nicotine and heavily restricted in the European Union because of its toxicity to bees, and pyrethroids, which are typically used to control mosquitoes and other pests.
Pollen was collected from May through September from hives placed in a nonagricultural meadow, the border of a cornfield planted with neonicotinoid-treated seeds and the border of a cornfield planted with non-treated seeds. The researchers waited until after crops had been planted to avoid the heavily contaminated dust that arises during the planting of neonicotinoid-coated seeds.
The samples collected showed that honeybees take the overwhelming majority of their pollen from uncultivated plants, particularly the family that includes clover and alfalfa. The researchers found 29 pesticides in pollen from the meadow site, 29 pesticides in pollen from the treated cornfield and 31 pesticides in pollen from the untreated cornfield. "These findings really illustrate how honeybees are chronically exposed to numerous pesticides throughout the season, making pesticides an important long-term stress factor for bees," says Long.
"Although crop pollen was only a minor part of what they collected, bees in our study were exposed to a far wider range of chemicals than we expected," says Krupke. "The sheer numbers of pesticides we found in pollen samples were astonishing. Agricultural chemicals are only part of the problem. Homeowners and urban landscapes are big contributors, even when hives are directly adjacent to crop fields."
The data leads Krupke to conclude that overall levels of pesticide exposure for honeybees in the Corn Belt could be considerably higher than previously thought. He says this is partly because scientific and media attention has tended to concentrate on the effects of crop-based neonicotinoids. Few studies, the researchers say, have examined how non-crop plants can also expose bees to pesticides. Looking at the overall environment of Midwestern honeybees and their movements could provide more accurate insights into what substances bees encounter, Krupke says.
The most common products found in the pollen samples were fungicides (used to treat crop disease) and herbicides (typically weed killers). The two main types of insecticides — neonicotinoids and pyrethroids — were also present. Neonicotinoids are more poisonous to bees and are primarily used on agricultural land while pyrethroids are typically used where pollinators are likely to be — near homes and gardens with a diversity of flowering plants. The study showed distinct spikes of pyrethroids during August and September, the period when many homeowners spray these chemicals to kill mosquitoes, hornets and other pests.
Long says she was "surprised and concerned" by the diversity of pesticides found in pollen. "If you care about bees as a homeowner," she cautions, "only use insecticides when you really need to because bees will come into contact with them."
Ultimately, healthy bees mean a more affordable and healthy diet for us. Cereals and berries are just part of it — hundreds of the plants we need for food are pollinated by bees and there are no means of coping without their activity. According to the ABF, "honey bees contribute more than $14 billion to the value of U.S. crop production." All is quite literally lost without them. "Poorly pollinated plants," says New Agriculturalist, "produce fewer, often misshapen, fruits and lower yields of seed with inevitable consequences upon quality, availability and price of food."