University of Maryland Extension

Pollinators and Pesticides

Pollinators, Neonicotinoid Insecticides, and a New Maryland Law

European honey bees, native bee species, and other pollinators in Maryland have suffered population losses in recent years. This has led to increased scrutiny of a widely used class of insecticides, known as neonicotinoids. Public concerns resulted in the passage of the Pollinator Protection Act of 2016 by the Maryland General Assembly. The law went into effect on January 1, 2018 and restricts the sales and use of neonicotinoid pesticides. Only farmers and certified pesticide applicators (or people working under their supervision) can apply neonicotinoid pesticides outdoors. So while neonicotinoid products may appear on store shelves in Maryland they cannot be applied outdoors by gardeners.


bumblebee

Bumble bee. Photo: David Cappert, Bugwood.org

What are neonicotinoid insecticides?

  • Kill insects by causing nervous system excitation, resulting in paralysis and death. Their chemical structure is similar to nicotine.
  • Active ingredients of neonicotinoids: acetamiprid, clothianidin, cyantraniliprole, dinotefuran, imidacloprid, nitenpyram, sulfoxaflor, thiacloprid, thiamethoxam.
  • Systemic action: the active ingredient is absorbed by leaves, stems, and roots and moves through the plant’s vascular system.
  • Persist in plants from months to multiple seasons depending on active ingredient, application rate, plant species, and environmental conditions.
  • Low risks to people, mammals, and other vertebrates. Imidacloprid, clothianidin, dinotefuran, thiamethoxam are considered by the US EPA to be highly toxic to honey bees. Acetamiprid is the least toxic neonicotinoid for bees but is more toxic to mammals (it’s on the US EPA’s reduced risk list).
  • Used by commercial growers and gardeners around the world. Some products are labeled for controlling fleas and lice on dogs and cats while others are labeled to control pests of turf, ornamental plants, and food plants.
  • Products may be applied to soil, seeds, and foliage, sprayed on bark, or injected into trees. Research has shown that neonicotinoids can move into pollen, nectar, and fruits.

Are they harming bees?

  • The consensus among researchers is that the interaction of multiple stressors and factors has contributed to honey bee and native bee population declines. These include parasites (especially varroa mite in honeybees), habitat loss, pesticides, climate change, and diseases.
  • There is no evidence that neonicotinoids caused colony collapse disorder, and the role of neonicotinoids in high honey bee mortality is not clear. Researchers believe that neonicotinoids pose a greater threat to native bee species than to honey bees.
  • Pollinators can pick up neonicotinoids from treated plants by ingesting 1) nectar and pollen from flowers, 2) honeydew excreted by aphids and other sucking insects feeding on plants, or 3) water droplets pushed out of plant leaves and stems at night (guttation).
  • Exposure to neonicotinoids can produce sub-lethal effects such as impaired foraging, navigation, and reproduction.
  • The U.S. Environmental Protection Agency has taken steps to reduce the risk of negative effects of neonicotinoids on non-target organisms. These include changes to pesticide labels regarding the timing of pesticide applications and other actions that will protect pollinators.

honey bee

Honey bee. Photo: Joseph Berger, Bugwood.org


What can I do to help pollinators?

Pollinators are essential for the reproduction of many native plant species, and to the production of food crops on farms and in gardens. Gardeners can help by reducing or eliminating pesticide use and growing plants that provide habitat, nectar and pollen for a wide range of pollinators. 

  • Most plant problems are caused by a host of environmental and cultural factors, such as weather extremes, compacted soil, poor location or installation, crowding, winter injury, and over-mulching. Yet insects and diseases usually get the blame! Use our resources to learn how to diagnose and prevent problems, distinguish between beneficial and pest insects, and manage pest problems without pesticides.
  • If you decide to use a pesticide, follow these tips to reduce risks:
    • Select the least toxic product and avoid broad-spectrum pesticides that target a wide range of insects
    • Select products listed by the Organic Manufacturers Research Institute (OMRI) or are on EPA’s Reduced Risk list whenever possible
    • Carefully read and follow label directions
    • Avoid spraying open flowers
    • Spray in the evening when fewer pollinators are active
    • Wear protective clothing and gloves
  • Some large chain stores are responding to public interest and demand by either phasing out or eliminating the sale of plants treated with neonicotinoids.  Ask your local garden centers and nurseries about the pesticides that are used to produce the plants they sell.
  • Learn about and plant for pollinators! See other resources below.

Sources

2015. PLOS One. Assessment of Chronic Sublethal Effects of Imidacloprid on Honey Bee Colony Health

2016. Journal of Economic Entomology. Survey and Risk Assessment of Apis mellifera (Hymenoptera: Apidae) Exposure to Neonicotinoid Pesticides in Urban, Rural, and Agricultural Settings

2013. PLOS One. Assessing Insecticide Hazard to Bumble Bees Foraging on Flowering Weeds in Treated Lawns

2015. Vermont Agency of Agriculture. Neonicotinoid Pesticides: Safety and Use.

Additional Resources

By Jon Traunfeld, Extension Specialist, University of Maryland Extension. Reviewed by Mike Raupp, Ph.D., Professor, UM Dept. of Entomology; Dennis vanEngelsdorp, Ph.D., Assistant Professor, UM Dept. of Entomology; Graduate students, UM Dept. of Entomology

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