The nation's declining populations of honeybees and bumble bees may have won a round in their struggle for survival.
Earlier this month, the Environmental Protection Agency (EPA) sent a letter to companies that had applied for permits to use neonicotinoid pesticides. The agency said it will likely not be in a position to approve most applications for new uses of these chemicals until pollinator risk assessments have been completed. The ruling doesn't affect products currently on the market or previously approved use permits, but it's one more indication that the agency is taking a closer look at neonicotinoids, which affect the central nervous system of insects and are a suspected link to colony collapse disorder and the rapid decline of bees.
Bees and other pollinators account for 85 percent of the pollination of all the world's flowering plants, according to the Xerces Society, a nonprofit organization that protects wildlife through the conservation of invertebrates. Bees also account for more than 30 percent globally of the plants that produce the foods and beverages we consume.
"Neonicotinoids are one of the most serious causes of downward negative pressure on pollinators," according to Keith Delaplane, a professor of entomology and director of the Honey Bee Program at the University of Georgia. In fact, he rates them as the second-leading cause of decline in the nation's honeybees, reserving the top spot for the parasitic Varroa destructor mite.
What are neonicotinoids?
"Neonicotinoids are a broad spectrum pesticide that get their name from their basic chemistry because it is close to that of nicotine," said Delaplane, emphasizing that the neonics, as they are often called, are not the same as nicotine. The neonicotinoids affected by the EPA's regulatory move are imidacloprid, dinotefuran, clothianidin and thiamethoxam. The neonicotinoid family also includes acetamaprid. They gained popularity in agricultural and commercial ornamental production because they are effective against a wide range of insect pests and considered less hazardous to humans and other vertebrates than other insecticides.
"The hallmark of neonicotinoids is that they are systemic," Delaplane added. That means they travel throughout a plant via its vascular system and distribute the chemical to all parts of the plant tissue 24/7, including its nectar and pollen.
"Neonicotinoids just hammer insects," Delaplane said. While there are many target insects, such as whitefly, Japanese beetles, emerald ash borer and others, neonicotinoids are used in general to control sucking and chewing insects and beetles. But some of the insects they "hammer" are important pollinators such as honeybees, bumble bees and solitary bees.
How neonicotinoids became a cause of concern
A PowerPoint presentation titled "Growing Flowering Plants That are Safe for Pollinators in the Yard and Garden" by David Smitley, a professor of entomology at Michigan State University who works closely with the turfgrass, nursery and floriculture industries on solving insect pest problems, includes neonics (as they are often called) in a timeline that traces the decline in honeybees.
According to the PowerPoint, honeybee decline began in the 1950s and sharply increased when parasitic mites were introduced into the United States around 1987. The neonicotinoid class of pesticides were introduced in 1994, but the rate of honey bee decline, while continuing, did not immediately get worse.
The rallying point against neonicotinoids for anti-pesticide activists occurred on June 2013 when 50,000 bees died in the parking lot of a Target store in Wilsonville, Oregon, near the Xerces Society headquarters. Scott Hoffman Black, executive director of the Xerces Society, said he confirmed the bees died from being sprayed with an insecticide that contained the neonicotinoid dinotefuran. He claimed the label instructions for using the pesticide were not followed.
In May 2014, a Harvard School of Public Health study linked low doses of neonicotinoids to colony collapse disorder, which was widely reported by the media. Additional studies produced mixed results with the conclusion that pesticides, including neonicotinoids, may have an impact on bee decline but the primary causes remained the varroa mite, lack of food and other causes.
How do pollinators absorb neonicotinoids?
Bees can absorb neonics in several ways. One is by drinking nectar or by transferring pollen. Another is through a process called guttation, which is the act of a plant sweating.
Corn, for example, sweats during the night. Bees can obtain water from guttation droplets, especially during dry weather.
Aphids, one of the real targets of neonicotinoids, insert their needle-like mouthparts into plant tissue and suck plant juice all day long rather than imbibing guttation droplets. The neonicotinoids are also in the sweet excrement, or honey dew, from the aphids, which honeybees collect. So it's possible for the honeybees to absorb neonicotinoids indirectly from a treated plant without ever visiting that plant.
How are neonicotinoids applied?
The most common form of applying neonicotinoids to agricultural crops is to treat seeds before they are sown rather than treating plants. The goal is to eliminate application issues such as drift that can cause collateral damage.
That doesn't always work out as planned, Delaplane said. There was a case in the Midwest, he pointed out, involving spring planting of neonicotinoid-coated corn seed. As the seed was being poured into the hoppers and run through the planters, insecticide-coated dust was released into the air.
There was so much dust that it formed a type of pink cloud that drifted off target onto nearby bee hives. Manufacturers have since tried to improve the formulation to prevent airborne drift, Delaplane said.
Also in 2014, Michigan State University conducted specific research about the use of neonicotinoids and made recommendations about their use for greenhouse growers that produce flowering annuals. In 2013, the EPA produced a strengthened bee advisory label. The agency required registrants of commercial pesticides that could be harmful to pollinators to include the label on packaging beginning in 2014.
A gardening center in Home Depot. (Photo: RustyClark/flickr)
Neonicotinoids in the retail trade
Perhaps the best way for home gardeners to know whether ornamental plants they purchase at retail garden centers or big box stores have been treated with neonicotinoids is to ask the staff or look at the plant labels. Smitley's PowerPoint, for example, points out that Home Depot, one of the large retail chains that controls the lion-size of the flower and nursery market, is requiring a label in each pot of plants treated with a neonicotinoid insecticide. (Home Depot did not respond to a request for information for this story.)
Lowe's, another major retail home garden plant source, is working with growers and suppliers of live plants to eliminate the use of neonics on plants that attract bees and other pollinators, said Steve Salzar, manager of Lowe's Corporate Communications. "Lowe's has set a goal to phase out the sale of products that contain neonic pesticides within 48 months as suitable alternatives become commercially available. Lowe's also plans to have brochures and fact sheets about pollinator health available in its stores."
"Lowe's is also encouraging growers to use biological pest control methods when practical," Salazar said. Neither seeds nor seedlings sold at Lowe's stores have been treated with neonicotinoids, he added.
In the meantime, "Lowe's will be tagging plants and nursery products with information highlighting bee health and encouraging customers to be mindful of pollinator health when using pesticides," Salazar said. "The timeframe for adding the tags to plants is being determined." This is being done in stores nationwide.
Photo: Parker Knight/flickr
What can home gardeners do?
Because neonicotinoids have been in the news, the public eye has been focused on plants at garden centers. Smitley says reports that these plants could potentially harm pollinators have been exaggerated. In fact, he believes that purchasing flowering annuals, perennials and trees is beneficial for bees and other insects. "The discovery of neonicotinoid insecticide in the leaves and flowers of some garden center plants should not stop (home gardeners) from buying and planting flowers because the benefit to bees far outweighs the potential risk," Smitley wrote in a paper titled "Planting Garden Center Flowers is Good for Bees and Other Beneficial Insects."
Plants in home gardens are not a primary source of food for bees, and even if neonics are present in some leaves and flowers of plants bought at retail centers, those plants will not necessarily be toxic to bees, says Smitley and here are some reasons why:
- Many bedding flowers, such as petunias, impatiens and marigolds, are not treated with neonicotinoids.
- Many trees and shrubs and all conifers are wind-pollinated and not visited by bees.
- Perennial flowers, roses, flowering shrubs and flowering trees will only have neonics in their pollen and nectar for the first year or two after they are planted. However, these plants will be a valuable resource for bees and other pollinators for many years to come.
- Bees feed on a large variety of flowering plants within a mile of their colony home. The presence of a neonicotinoid in one plant will be diluted when the bees feed on untreated plants.
- Flowers in flats should be completely safe to bees.
Still, Smitley said in the paper that homeowners can take steps to help ensure bee safety with purchased perennial flowers and flowering trees.
These steps include:
- Removing the flowers in their first year in your garden or plant trees after they have finished flowering.
- Avoid spraying plants in your garden with insecticides, and never spray the flowers.
If holes that insects chew in leaves become unsightly, bee-friendly insecticides include products containing Bacillus thuringiensis (B.t.) and horticultural oils and soaps, according to Smitley's paper. B.t. can be used any time for caterpillars, and soaps and oils are safe to bees if sprayed early in the morning before bees are present. Be careful not to exceed the application rate on the product label, because at higher concentrations soaps and oils can cause plant injury.
Safe for humans
Neonicotinoids should not pose any threat to humans if they are used according the product label and stored in places not accessible to children. They have a low toxicity for all mammals, said Delaplane.
In fact, said Smitley, the most widely used neonicotinoid insecticide, imidacloprid, is less toxic to people than caffeine, and about twice as toxic as ibuprofen.
Smitley offered a calculation that puts the toxicity of neonicotinoids for humans into perspective. Based on the required studies with laboratory rats, he has concluded that once garden center products containing imidacloprid are mixed into a bucket of water for use as a drench around the base of a tree, the toxicity of that solution to people is about the same as the toxicity of wine.
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- It's not just bees: Popular pesticides are killing birds, too
- How to garden for bumblebees
- 12 plants that repel unwanted insects
Photo of man spraying pesticides: Iakov Filimonov/Shutterstock