In response to the November 2018 New York Times article entitled “The Insect Apocalypse is Here,” which reported sharp declines in insect numbers, many gardeners set out to remedy the problem by planting bee- and butterfly-friendly gardens. But some plants in these gardens may not actually help. 

Most nursery plants — including those attractive to pollinating insects, butterflies and birds — receive treatment with a class of insecticides called neonicotinoids. Increasingly studies show that these “neonics” harm far more than their insect targets and persist in plant tissues for months or years.

Many people first became aware of neonics in June 2013 when more than 50,000 bumblebees died in Wilsonville, Ore., after 55 linden trees in a Target parking lot were sprayed with dinotefuran. The resulting furor made headlines for months, but then faded away. The neonics remain in use, killing unintended organisms at a time when ecosystems urgently need strengthening. 

Chemically similar to nicotine, neonics were first introduced in the 1980s as a less-toxic alternative to organophosphates since they are not very toxic to mammals. Today, imidacloprid alone is the most widely used pesticide in the world and since there many other pesticides comprise this group they are ubiquitous in both agriculture and the home garden. 

Neonics work by binding to nerve cell receptors and over-exciting neurons causing cell inactivation or death. Studies show that they disrupt navigation and reproduction in bees.

New research by the University of Saskatchewan confirms that neonics not only negatively impact insects, they also harm birds. White-crowned sparrows fed a single, measured dose of imidacloprid lost 6 percent of their body weight and increased their migratory stopover by 3.5 days, presumably to regain lost body mass. Scientists believe ingesting the neonics results in appetite suppression. This severely impacts birds feeding in contaminated fields during migration.

With corn, soybeans and many other crops, farmers coat seeds in the neonics. The insecticides dissolve in water for soil drench application. Plants then incorporate the toxins into leaves, pollen, nectar and other tissues. Growers may also spray neonics directly on plants.

“Nurseries are only required to apply neonics to their stock in the case of citrus, within quarantine areas,” said Dr. Andrew Sutherland, the UC Urban IPM Advisor for the San Francisco Bay. “All other nursery applications of these insecticides are voluntary, usually meant to keep stock free of aphids, whitefly and mealybugs. This is because many shoppers — no matter how green their thumbs or hearts — are reluctant to buy plants with even a single pest present.”

What to do? 

“I can’t give a blanket recommendation about when it’s safe to expose insects to treated plants because it really depends on the type of neonic used, when it was used, how much, growing conditions, etc.,” said Emma Pelton from the Xerces Society. “Some neonics persist for years! For these reasons, we really urge people to ask nurseries the hard questions and source neonic-free plants whenever possible.”

In addition to asking about neonics, gardeners can grow their own plants from seed or trade cuttings and “volunteer” seedlings with neighbors. Pollinator, bee and bird gardens are vital to promoting healthy ecosystems. Through education and insisting on neonic-free plants, consumers can help themselves and their communities. 

For more information, refer to these Xerces Society publications: https://xerces.org/neonicotinoids-and-bees and https://xerces.org/wp-content/uploads/2013/06/NeonicsInYourGarden.pdf.