The decline in numbers of European honeybees, bumblebees and other native pollinators has been well documented for over a decade. Research exploring pollinator decline began in earnest in 2006 when Colony Collapse Disorder, affecting honeybees, first appeared. In 2006 and 2007 managed honeybee colonies experienced a loss rate of over 30 percent. There was great concern that the loss of pollinating honeybees could negatively affect agricultural production including our local almond crop. Although managed honeybee colonies rebounded (thanks to improvements in hive management), hive losses from April 2018 to April 2019 reached 40%, the highest loss since monitoring began, primarily due to reduced effectiveness of Varroa mite control materials.

Studies conducted by the Bee Informed Partnership, the Xerces Society, and other groups indicate a combination of factors have contributed to honeybee losses. Factors include: habitat loss; drought; poor nutrition; parasites such as Varroa mites; pathogens such as fungi and viruses; and exposure to pesticides. While research initially focused on honeybees, more recent studies focused on native bees and other pollinators, specifically the role played by a class of pesticides called neonicotinoids (neonics).

Neonics are a nicotine-derived class of pesticides developed for use on both farm crops and landscape plants. Approved by the EPA in the 1990's, this group of neurotoxins are the most commonly applied group of insecticides in the world.

In a number of cases, neonics have been implicated in mass die-offs of native bumblebees: for example, a mass die-off of bumblebees in Oregon has been attributed to an application of a neonic pesticide on linden trees.. This has spurred additional research on native pollinators, and we now have a better understanding of how neonics travel in our plants, soil, air and water. This new research led the U.S. Fish and Wildlife Service to phase out neonic use on National Wildlife Refuges in 2016. In 2018, the European Union banned all outdoor use of several neonics. (See, for example, the Xerces Society report How Neonicotinoids Can Kill Bees: The Science Behind the Role These Insecticides Play in Harming Bees, 2016).

No direct link has been found between neonics and the Colony Collapse Disorder of honeybees. Although not clearly understood, neonics may weaken the honeybee immune system, thus making the bees more susceptible to pathogens and diseases. Research has also found that bumblebees and solitary bees are affected differently than honeybees. A study at Worcester Polytechnic Institute in Massachusetts discovered that queen and male bumblebees suffer much higher rates of mortality compared to that of worker bees. This negatively affects the ability to form new colonies.

The neonics have several characteristics that are causing alarm. They are systemic pesticides, meaning they are absorbed into a plant's tissue. Systemic pesticides can be applied in a number of ways: by drenching the soil; injecting directly into plants; used as a spray; and applied as a seed coating. As these pesticides are absorbed, plant tissue, pollen and nectar become toxic. Pollinators who visit flowering plants to collect pollen and nectar are then exposed to the pesticide. The Xerces Society report noted above states that even small levels of neonics can affect the ability of bees to navigate and impair their sense of taste. These are important factors in their ability to forage for food.

Neonics are long lasting; they can persist in the soil for months, but can last years in woody plants. When used to protect corn and other seeds, they can remain in the soil to be absorbed later by other untreated plants.

In addition to agricultural crops, native flowering plants also depend upon pollinators. The Xerces Society argues that fewer pollinators may lead to a decrease in native flowering plants and the wildlife that depends upon those plants (Chapter 1, “Why Care About Pollinators?” in Attracting Native Pollinators: Protecting North America's Bees and Butterflies, Xerces Society, 2011).

Because many products approved for home and garden use can be legally applied at rates significantly higher than the rates approved for agricultural crops, home gardeners may unwittingly be exposing pollinators to toxic levels of pesticide. Neonic pesticides found in common home and garden products include imidacloprid, clothianidin, thiamethoxam, acetamiprid, and dinotefuran.

What can you do to help? Read the label! Avoid using systemic neonic products in your garden by checking the active ingredients listed on pesticides and fertilizers. Ask local nurseries if plants or seeds they sell are treated with a neonic product. Several major home and garden retailers have already agreed to eliminate neonic-treated plants from their nurseries. When applying a fertilizer avoid fertilizer-pesticide combinations because many of them contain neonics. If worm control is warranted, turn to an organic pesticide such as Bt (only effective on worm pests). Practice Integrated Pest Management (IPM) techniques to control garden pests (see http://www.ipm.ucdavis.edu/). Remember that chemical pesticides can affect all insects, including ladybugs and other beneficial insects that keep destructive pests such as aphids under control.

Most importantly, create a pollinator-friendly garden by planting patches of pesticide-free flowering plants. Try to provide food sources for pollinators throughout the year. The Xerces Society is a great resource for more information on the dangers of neonics and how to create a pollinator-friendly garden: http://www.xerces.org.

The Butte County UC Master Gardeners are part of the University of California Cooperative Extension (UCCE) system, serving our community in a variety of ways, including 4H, farm advisors, and nutrition and physical activity programs.  Our mission is to enhance local quality of life by bringing practical, scientifically-based knowledge directly to our community. For more information on UCCE Butte County Master Gardeners and their upcoming events, and for help with gardening in our area, visit https://ucanr.edu/sites/bcmg/. If you have a gardening question or problem, call our Hotline at (530) 538-7201 or email mgbutte@ucanr.edu.

Examples of neonicotinoid ingredients found in common garden insecticides:

Imidacloprid Clothianidin Thiamethoxam Acetamiprid Dinotefuran