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Pesticides and Pollinators

All pollinators are vulnerable to a number of different pesticides. Application of pesticides on flowering plants is the greatest hazard. In 1889, William B. Alwood, horticulturist and pest management specialist at Virginia Agricultural and Mechanical College (now Virginia Tech) cautioned grape growers in Albemarle County (VA) to not spray their grapes when in bloom to avoid killing honey bees. Professor Alwood's advice is the most important practice of pollinator protection when dealing with pesticides.

Protecting Honey Bees

The poisoning of honey bees and other beneficial insects by pesticides can be a serious problem. Honey bees provide a valuable service to agriculture because they are the most important pollinators of cultivated crops. They also produce honey and beeswax. Efforts should be made to protect honey bees whenever pesticides are used. The protection of honeybees has become even more critical in recent years because of increased colony loss due to mite parasites and Colony Collapse Disorder (CCD).

Causes of Bee Poisoning

  1. Most bee poisoning occurs when insecticides are applied to crops in bloom. This includes crop plants such as sweet corn, which is routinely sprayed when in tassel. Honey bees collect pollen from corn tassels.
  2. The application of insecticides to fields with weeds that are in bloom. The spring application of insecticides to alfalfa fields with flowering weeds is a particular problem in Virginia.
  3. Drift of toxic sprays or dusts onto adjoining crops or weeds that are in bloom.
  4. The contamination of flowering ground-cover crops in orchards when spray applications are made.
  5. The contamination of water. This includes water collected by bees for drinking and cooling the hive as well as contact with contaminated water or dew on foliage or flowers.
  6. The use of systemic insecticides and the possible contamination of nectar and pollen. This is a concern with the use of neonicotinoid insecticides, such as clothianidin, imidacloprid, and thiamethoxam, although more research is needed.


The most serious problems occur when bees collect contaminated pollen or nectar and carry these materials back to the hive. Insecticidal dusts (particularly Sevin) and encapsulated insecticides are especially dangerous because they adhere to foraging bees and may be collected and stored in the hive with pollen. Such materials can cause serious bee kills within the hive for many months.


Ways to Reduce Bee Poisoning

  1. When using pesticides that are hazardous to bees, notify the beekeeper so that he may move or protect his hives.
  2. Do not apply insecticides that are toxic to bees to crops in bloom.
  3. Use insecticides that are less toxic to bees when such choices are consistent with pest control recommendations (see the table of relative toxicities).
  4. Choose the least hazardous formulations when possible. Dusts and encapsulated insecticides are more toxic than sprays of the same material. Wettable powder sprays tend to have a longer residual effect (and are more toxic) than emulsifiable concentrate sprays. Granular applications are usually the safest method of treatment around bees.
  5. Avoid drift of toxic sprays onto ground-cover plants, weeds, and crops in nearby fields.
  6. Control weeds in fields and avoid direct insecticide applications to flowering weeds whenever possible.
  7. If ground-cover plants in orchards are in bloom, mow before spraying.
  8. Apply insecticides when bees are not actively foraging, either in the late evening or early morning. This is particularly important with crops such as corn where evening applications avoid many problems since pollen release occurs in the morning. In general, evening applications are least hazardous.
  9. Do not apply insecticides when temperatures are expected to be unusually low following treatment. Residues remain toxic to bees for a longer time under such conditions.
  10. Avoid direct treatment over colonies.
  11. Contact beekeepers with nearby colonies before treatment so that they can move the hives or confine the bees if potential bee losses might occur.


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