Poisoned Pollen

Poisoned Pollen Photo Credit: Cory Barnes via flickr (http://bit.ly/29ANJkG). Creative Commons (CC BY-SA 2.0)

The wide variety of pollen bees consume exposes them to harmful pesticides.


A bumper crop of poisoned pollen. I’m Bob Hirshon and this is Science Update.

Bee experts worry that honeybees in farm communities will suffer because they consume pesticide-laced pollen from nearby crops. But in the journal Nature Communications, Purdue entomologist Christian Krupke reports that even with a large source of corn pollen nearby, bees roamed great distances.

These bees were sampling the environment for us and they were bringing back the message that there are many sources of exposure out there, and even if you put them right beside a cornfield, they don’t have that cornfield’s signature. They don’t have just those pesticides.

The bees picked up pollen from residential gardens, laced with pesticides not used on farms and even insect repellents and other chemicals. He says the take-home message is that to protect bees and other pollinators, homeowners need to join farmers in controlling pesticide use. I’m Bob Hirshon, for AAAS, the science society.

Making Sense of the Research

Many entomologists (scientists who study insects) have been concerned for some time about the declining honeybee populations and have been trying to discover what has been causing this decline. Potential causes have ranged from the loss of habitat to disease. The research conducted by Christian Krupke and his colleagues seems to provide some answers.

When most of us think of the use of pesticides, we tend to think about big farms and the spraying of crops to protect them from harmful insects. Entomologists are concerned about these pesticides because of the possible harm they can do to honeybees. One example of potentially harmful pesticides are neonicotinoids, which some research has implicated in the decline of bees, that are used to coat seeds and are known to be found in corn and soybean pollen. This research, however, points to another source of potentially harmful pesticides: people's homes.

Dr. Krupke and his colleagues conducted their research in West Lafayette, Indiana, with bees next to cornfields. They found that these bees spent only a minority of their time feeding on the corn crops. Instead, they mostly sought out pollen from flowering weeds, trees, and gardens nearby. In fact, the bees collected pollen containing up to 32 different pesticides, most of which didn’t originate from crops or agricultural applications. Some of the pesticides that researchers found in the bee pollen included pyrethroids, which are generally used in households to repel insects and are highly toxic to bees. In addition to the pryethroids, researchers also found DEET, which is a mosquito repellent.

The researchers aren't sure about how these pesticides end up in pollen. They theorize, though, that since many of the pesticides are water soluble (able to be disolved in water), they are likely absorbed by plant roots through the soil. This means the pesticides can contaminte the plants and their pollen.

What's really so troubling about the findings of this study is the number of pesticides found in the pollen. When researchers study the effect of these kinds of chemicals, they tend to do so in isolation. They don't know how being in contact with so many different types of pesticides will impact the honeybees. “You can imagine that if you have many at a time, you could have enhanced toxicity,” says Krupke.

Now try and answer these questions:

  1. What are some possible causes for the decline in honeybee populations?
  2. What is an entomologist?
  3. Why are entomologists concerned about pesticides' effect on honeybees?
  4. Where did the researchers conduct this study?
  5. What did they learn from gathering the pollen collected by the honeybees?
  6. How do you think all of these pesticides ended up in the pollen?

You can listen to Farmers & Pesticides to learn more about the effects that pesticides can have on human health.

Going Further

For Educators

You can help extend the ideas in this Science Update by having your students listen to Nitrogen Pollution, which focuses on how human sources of nitrogen may be just as environmentally costly as carbon emissions.

If your students want to read more about this research, they can go to Honeybee Pollen and Pesticides in Your Garden, which provides an overview of the study.

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