Lesson 68: Pesticides and Your Bees

How bees get exposed, how to recognize a pesticide kill, and how to protect your colonies

Your bees forage over thousands of acres around your hives: farms, gardens, lawns, roadsides. Anything sprayed on a flower they visit can come home with them. Pesticide exposure is one of the stresses on honey bee health, along with mites, diseases, poor nutrition and management. You can't control what your neighbors spray, but you can reduce the risk and know what to do if it happens.

How bees are exposed

• Direct spray or drift: a product lands on foraging bees, or drifts onto flowers they're working, including blooming weeds in or beside a crop field.
• Contaminated pollen and nectar. Systemic insecticides (such as the neonicotinoids) are taken up by the plant and can show up in its pollen and nectar, sometimes long after application. They can also be taken up from treated soil by non-crop plants nearby.
• Dust from treated seed: planting seed coated with insecticide can raise toxic dust that bees fly through.
• Contaminated water: bees often drink from puddles, ponds and ruts where runoff collects.
• Inside the hive: foragers bring contaminated food home, where nurse bees and brood eat it.

Insecticides are the most toxic to bees, but some fungicides and other products can also cause problems, especially in combination. Low (sub-lethal) doses may not kill bees outright but can weaken the colony or make viral infections worse (lesson 62).

Recognizing a pesticide kill

A pesticide kill usually shows up fast: - Large numbers of dead and dying bees in front of the hive or on the bottom board, seemingly overnight; there weren't any the day before. - Trembling, twitching, uncoordinated or crawling bees (most insecticides are nerve poisons). - Sometimes dead brood, or larvae crawling out of cells, if poisoned food reached the nest. - Some kills are invisible at the hive, because foragers die in the field and the colony just shrinks.

Don't confuse it with varroa:

Finding dead bees doesn't always mean pesticides. Check the symptoms carefully (lessons 62, 67).

If you suspect a pesticide kill

1. Act fast, while the evidence is fresh.
2. Take photos and write notes: date, time, what you see, what's blooming, any spraying you saw nearby.
3. Collect a sample: at least 100 dying or freshly dead bees in a clean, dry container (glass is best), plus an ounce or two of comb with pollen or honey if possible. Freeze the samples to keep them from breaking down.
4. Report it to your state department of agriculture's pesticide program (the agency that enforces pesticide labels). EPA also accepts bee-kill reports. Without a prompt report, the cause usually can't be proven.

Reducing the risk

Where you put your bees is the biggest decision (lesson 24). Where you can, choose a site away from heavily sprayed crops.

Talk to your neighbors. - Let nearby growers, applicators and your county Extension office know where your hives are. Many states and beekeepers use a free online registry (FieldWatch/BeeCheck) that tells applicators where hives are. - Ask to be told before spraying, ideally the evening before. - Register your hives with your state (lesson 4); inspectors and applicators may use that information.

When a spray is coming: - For short-lasting products: confine the bees the night before and for the day of spraying (screen the entrance), with ventilation and water so they don't overheat (lesson 67). With only one or two hives, running a sprinkler over them can keep bees home, since they act as if it's raining. - For long-lasting products on crops your bees are visiting: move the hives at least 3 miles away (so foragers don't return to the old spot).

What growers and homeowners can do (and what you can suggest): - Spray only when there's a real pest problem, not "just in case." - Don't spray plants in bloom, including blooming weeds in the field; mow flowering weeds first. - Spray in the late evening, at night or very early morning, when bees aren't flying, and not when it's windy. - Choose products less toxic to bees, and avoid dusts. - Read the label: its "bee hazard" and environmental statements say whether a product is toxic to bees or systemic.

At your own home: don't use insecticides near your hives, and choose bee-safe practices in your own yard and garden (lesson 82).

What to remember

• Bees are exposed through spray and drift, contaminated pollen and nectar (systemics), seed dust, and water.
• Pesticide kill: sudden piles of dead, trembling bees. Varroa: slow dwindling in late season.
• Suspect a kill? Photograph, sample 100+ bees, freeze, and report quickly to your state agriculture department.
• Prevent it: good site choice, tell your neighbors and use the hive registry, confine or move bees when needed, and encourage spraying outside bloom and outside flight hours.

Quick check

1. You find thousands of dead and twitching bees at the entrance one morning. What's the likely cause, and what should you do?
2. What's a systemic insecticide, and why does it matter to bees?
3. A neighbor is spraying a long-lasting insecticide on a crop your bees are visiting. What are your options?

Adapted from: Krupke, Hunt & Foster, Protecting Honey Bees from Pesticides (Purdue Extension E-53, 2021); Penn State Extension, Pesticides and Pollinators; U.S. Environmental Protection Agency, Protecting Bees and Other Pollinators from Pesticides and Pollinator Health Concerns; Shimanuki & Knox, Diagnosis of Honey Bee Diseases (USDA AH-690, rev. 2000); Penn State Extension, Viruses in Honey Bees (2026).

Adapted from university Extension sources. Experienced Georgia beekeepers are reviewing these lessons. See something that doesn't match your experience? Tell us.