Pesticides & Pollinators

“Just one little spray,” you think, staring down the latest pest to invade your home or lawn. “What harm could it do?” 

Before you reach for the big box bug bomb, let’s pause for a look at the bigger picture, which is that pollinators are being harmed by irresponsible pesticide use—but it’s not too late for you to make a difference.

The Importance of Pollinators

According to the USDA, pollinators are responsible for one out of every three bites of food we consume. Crazy, huh? Overall, more than 100 U.S.-grown crops rely on native bees, honey bees, bats, birds, butterflies, wasps, moths, beetles, and small mammals. Of all these pollinators, native bees and honey bees are some of the most at risk and, according to the USDA, honey bee colonies have been showing declines for over three decades.

This is likely due to a variety of factors, including colony management practices, pollutants, reduced species diversity, climate change, parasites, poor nutrition, pathogens, habitat loss, and crop and land management pesticide use. 

While some of these factors may be out of our control on an individual level, the last two are quite accessible! More on those in a bit.

How Pesticides Harm Pollinators

Now that we have your attention, let’s start from the beginning. What’s a pesticide?

A pesticide is any chemical—natural or synthetic—that controls or kills weeds (herbicide), insects (insecticide), diseases (fungicide), and more.  Of these three categories, insecticides—especially neonicotinoids or “neonics”—are the most harmful to bees, either through direct or indirect exposure. 

While neonics and other insecticides are the most likely to be toxic to bees, other pesticides should still be used with caution. Fungicides, for example, can disrupt adult bee foraging behavior, so it’s best to apply them in the evenings when pollinators are less active. Herbicides have fairly minimal direct toxicity, but if they’re used excessively they may deplete those yummy sources of nectar and pollen that bees rely on for survival. 

But there’s more to the equation than population decline. Non-lethal effects include impaired learning, disorientation, impaired foraging, reduced immune response, reduced growth, reproductive impacts, and a decrease in colony longevity; these effects can be immediate or long-term.

In an effort to reduce impact on pollinator populations, pesticides are now labeled for their direct bee toxicity. In pesticide parlance, this is called LD50, or the amount which kills 50% of exposed bees during controled experiments. If this number is less than or equal to 2 micrograms per bee, the pesticide is considered highly toxic to bees (Toxicity Category I); if the number is greater than 11 micrograms per bee, it’s considered relatively nontoxic (Toxicity Category III). Category III products do not require a bee caution statement on the label.]


Did You Know? In the U.S., neonicotinoids are used on about 95% of corn and canola crops, as well as the majority of cotton, sorghum, sugar beets, and soybeans.

How Pollinators Encounter Pesticides

If only it were as simple as saying “Don’t spray pollinators with chemicals!” While that is certainly a potent method of exposure (seriously, don’t do that), it’s one of several ways that pollinators can encounter pesticides:

  1. Direct topical exposure: This occurs when a bee is foraging in or visiting an area when pesticides are being applied. This can cause immediate harm to the affected bee, or the pesticide can be carried back to the colony.
  2. Indirect topical exposure: This occurs when a bee visits a flower or other surface that was previously treated with a pesticide. 
  3. Drift: This occurs when the wind blows chemicals from one area to another (Hint: Get to know your neighbors and convince them to avoid harsh pesticides!).
  4. Oral ingestion: This occurs when bees feed on the pollen or nectar of a plant that was treated with a systemic insecticide, or a plant that was grown in soil treated with an herbicide.

Contaminated water or pesticide spills: This occurs when honey bees collect contaminated water to help cool their hives.

Ways to Avoid Exposure

It’s possible to be a steward to our pollinators without allowing weeds and pests to take over. As always, our first recommendation is to practice Integrated Pest Management, which involves prevention, proper identification, and habitat reduction to reduce the amount of chemical inputs needed. Here are some other key tips!

 

DO:

  1. Choose the least toxic, least persistent pesticides, and use only the amount needed. Using excess product is not more effective and can actually cause the development of pesticide resistance over time.
  2. Read label instructions on all pesticides! Really, it’s the law.
  3. Remove flowers before spraying to avoid pollinator activity.
  4. Spot treat problem areas rather than using blanket applications—using what you need, where it’s needed, when it’s needed.
  5. Apply pesticides in the late evening whenever possible. Not only is this when pollinators are the least active, but also it allows the product to dry before morning foraging.
  6. Clean up any pesticide spills as instructed by the label.

 

DO NOT:

  1. Spray pesticides (even organic ones!) on flowering plants.
  2. Apply near or on water sources (puddles, ponds, bird baths, etc.).
  3. Apply pesticides when it’s windy.
  4. Apply before rain or heavy dew.
  5. Throw pesticides in your regular trash can! Proper disposal instructions can be found here.

 

In addition to all the above ways to avoid harming pollinators, there are things you can do to proactively help them. Our favorite? Growing native plants! In addition to benefiting our key pollinators, it offers a beautiful, low-maintenance enhancement to your yard. Win-win.

Cited Sources

Andrews, H.M. and M.A. Rose. Protecting Pollinators While Using Pesticides. The Ohio State University.  

Grozinger, C. and S. Fleischer. Pesticides and Pollinators. PennState Extension. 

May, E. Minimizing Pesticide Risk to Bees in Fruit Crops. Michigan State University Extension. 

Straw, E.A., E.N. Carpentier and M.J.F. Brown. Roundup causes high levels of mortality following contact exposure in bumble bees. Journal of Applied Ecology. 

Xerces Society. The Risk of Pesticides to Pollinators

USDA. U.S. Pollinator Information.