Another Pesticide Controversy: Neonicotinoids and Pollinator Decline
A class of pesticides called neonicotinoids, neuro-active systemic insecticides chemically similar to nicotine, are currently under scrutiny for harming pollinators. There is the familiar argument between manufacturers who claim that no adverse effects on bee colonies have been observed “at field-realistic exposure conditions” and scientists and pollinator advocates saying the opposite. Let’s sort things out.
First off, there’s the pronunciation issue. Here is phonetic guidance on how to say “neonicotinoid”. This mouthful is often shortened to “neonic” — pronounced “nee-oh-nick” for convenience. There are six compounds that make up the neonic population: acetamiprid, clothiandin, dinotefuran, imidacloprid, thiacloprid, and thiamethoxam. Manufacturers of the technical ingredient include BayerCropScience, Syngenta and Valent. Other companies formulate and sell products for commercial and home use. Examples of neonic brands are listed here.
Photo: Imidacloprid on label: risdmaharamfellows.com
How They are Used
Neonics are systemic pesticides that kill a variety of pests including sap suckers and leaf chewers like aphids and root feeding grubs. They are taken up by the plant and transported throughout its tissues, including leaves, flowers, roots, stems, pollen and nectar. They are commonly applied via a seed coating or soil drench to be taken up by roots, or when spray applied, to be absorbed through foliage. They may also be utilized as tree injections and as granules.
They attack the central nervous system of insects when ingested, preventing transmission of nerve stimuli, causing paralysis and death. The affected neural pathways are more sensitive in insects than mammals, making neonics more toxic to insects than mammals.
Neonics remain in plants for weeks after treatment, and they degrade slowly, lasting months or years in soil and leaching into groundwater under some conditions. Their presumed benefit when introduced in the 1990s was that they are effective in lower concentrations than older organophosphates and carbamates, and that seed treatments were felt to be more effective than spraying. Ironically, their systemic action, persistence in crops and soil, and potency in low concentrations make them useful against targeted pests but harmful to non-target organisms including pollinators.
Neonicotinoids are the most widely-used class of pesticides worldwide, used on 140 crop varieties, including cereals, cotton, legumes, potatoes, orchard fruits, rice, and vegetables. They are also used on turf, ornamentals, timber and in pet tick and flea collars.
Early studies of neonic effects on pollinators were criticized for not being representative of real world conditions. However several peer-reviewed studies published since 2017 were conducted in the field and appear to have confirmed the link between use of various neonics and damage to pollinator health. Interestingly, the preponderance of honey bee exposure in a Canadian study was determined to be from pollen in non-target plants, indicating possible dispersion of neonic substances as dust from seed during planting. Similar results have come from multiple studies of rapeseed in Europe. The effects include pollinator death following high exposures, and decreased overwintering survival, lowered immune response, and reduced reproduction from lower exposures. There is also an alleged increase in toxicity when some common fungicides and neonics are used in the same agricultural fields.
Neonic plant tag: Photo Jill Staake, birdsandblooms.com
While there is still some dispute from manufacturers, the data linking neonicotinoid use to pollinator decline is only strengthening. Certain neonics have been outlawed by the European Union since 2018. Here in the U.S., the EPA is evaluating its stance on these pesticides. Its final risk assessment and interim regulatory decision is expected to be issued in the near future. Although pollinator health is not likely harmed by occasional exposure to neonic-treated plants, numerous retailers, including Lowes and Home Depot, have committed to eliminating the sale of neonic-treated plants and to labeling those that are treated until the practice is eliminated. The world is moving in the right direction; it is a question of whether we are moving fast enough.
Alternatives to Neonicotinoid Use
As is the case with most toxic agricultural chemicals, there is no alternative that is as convenient to use and, at least in the short term, as deadly to pests as neonicotinoids. But, as we see the unplanned harm that they do and as the inevitable resistance of targeted pests increases, we come to understand that the long-term solution is managing pest damage, not futilely trying to eliminate pests.
Pyrethroids, synethetic pesticides with chemical structures similar to pyrethrins, were thought to be a potential neonic replacement. Pyrethrum is a naturally-occurring mixture of chemicals found in certain chrysanthemum flowers, and it was first recognized as having insecticidal properties around 1800 in Asia. The manufactured pyrethroids, however, have higher levels of toxicity than the natural pyrethrins. Their toxicity to beneficial insects, pest predators and parasitoids, risk to aquatic insects, and risks of secondary pest outbreaks argues against the expanded use of pyrethroids.
In 2014, Bayer announced, and the EPA approved, registration of a new pesticide, Flupyradifurone, claimed to be safer for bees. However, testing to date is inconclusive. Testing has not been representative of real world commercial agricultural conditions concerning non-targeted plants and potential synergistic effects with other commonly-used agricultural chemicals. Given its similar chemical structure to neonics, it seems like it was initially overhyped by the manufacturer.
The recommended approach to pest control is via an Integrated Pest Management (IPM) practice. The IPM concept is valid for both commercial agriculture and home gardeners. It is an eco-system based strategy with:
- a long term prevention focus utilizing:
- cultural practices
- biological controls
- habitat manipulation
- resistant plant varieties
- using pesticides only when necessary based on a documented monitoring approach
- removing only the target organism
- selecting actions to minimize hazards to humans, beneficial and non-target organisms, and to the environment
Because IPM practices are targeted at specific identified pests, an indiscriminate preemptive approach like treating seeds with a systemic pesticide isn’t allowed. IPM is a process that follows these steps:
- Monitoring: inspection to determine specific pest type(s) and infestation levels
- Record keeping to establish trends/patterns, including dates, pest identification population, distribution, prevention plan, treatment plan
- Action levels: action plan for particular pests and population sizes
- Prevention plan: the primary means of pest control
- Tactics and criteria:
- Cultural, biological, and structural tactics
- Chemicals as a last resort, using the least-toxic first to minimize possible harm to humans, non-target organisms, and the environment
- Post action assessment: what worked, what didn’t, how should we revise the plan for next time?
Home Gardener Approach
The major risk to pollinator populations derives from chemical-based commercial agriculture, where pesticide application is widespread in anticipation of infestations and often not successfully confined to target crops or target pests. At home, it makes sense to follow the IPM protocol, perhaps a little less formally, but in principle. The concept is to treat causes of pest infestation as infestations occur and to manage pest damage naturally and only on an as-needed basis, rather than chemically on a predetermined schedule.
Cultural practices may include:
- Regular compost additions to maintain a healthy population of soil organisms
- Crop rotation to avoid inadvertently helping pests thrive via monoculture
- Intercropping and companion planting to attract beneficials while reducing attraction of and potentially warding off pests
- Using physical barriers like fine mesh netting and row covers to prevent pests from reaching crop plants
- Hand removing larger pests from plants when practical
- Maintaining garden hygiene by removing diseased and end of season vegetation from the garden and disposing of it properly.
Photo: Ladybug larva preying on pests (by Ralph Morini)
Biological and habitat controls include:
- Importing predators and parasitoids that prey on the pests of concern. Note that specific pests demand specific predators and predators need a food source to stay in the garden area.
- Maintaining a chemical-free habitat that is welcoming to beneficials and pollinators
Using resistant plant varieties means researching and selecting the best available hybrids that are resistant to likely pest challenges.
When nothing else works and damage levels warrant continued action, research the organic and manufactured-chemical options for the specific pest in question. Insecticidal soaps are a good option for many sucking and chewing pests. Neem oil is similarly safe on food with no dangerous residues while killing or reducing pests, powdery mildew, and other fungal infestations.
If there is no good option but a neonic or other relatively toxic chemical, follow label directions carefully, use it minimally, and definitely avoid spraying open flowers and applying it during the day when pollinator activity is highest.
The Harder Path is the Right Path
As is so often the case, the more convenient approach, using neocotinoids and other chemicals on a widespread basis in anticipation of pest problems, is seductive but harmful longer term. Damage to pollinators, faster evolution of resistant pests and replacement of natural processes with chemicals are all costs that eventually have to be faced.
While commercial agriculture is where the large scale damage is done, home gardeners also have a role to play in changing practices and setting a tone for changing societal priorities. The IPM approach requires more work and acceptance of a certain amount of pest damage but it is definitely more sustainable longer term. We have to reduce and manage the use of neonicotinoids and other agricultural chemicals or their long term impact will be far more harmful than beneficial.
“Study strengthens link between neonicotinoids and collapse of honey bee colonies,” https://www.hsph.harvard.edu/news/press-releases/study-strengthens-link-between-neonicotinoids-and-collapse-of-honey-bee-colonies/
“Schedule for Review of Neonicotinoid Pesticides,” EPA, https://www.epa.gov/pollinator-protection/schedule-review-neonicotinoid-pesticides
“Chronic exposure to neonicotinoids reduces honey bee health near corn crops,” (Science, 2017), http://science.sciencemag.org/content/356/6345/1395
“Protecting Bees from Neonicotinoid Insecticides in Your Garden,” Xerces Society, https://www.xerces.org/wp-content/uploads/2013/06/NeonicsInYourGarden.pdf
“What Is Integrated Pest Management (IPM)?” University of California, https://www2.ipm.ucanr.edu/What-is-IPM/
“What is Integrated Pest Management?” Beyond Pesticides (formerly National Coalition Against the Misuse of Pesticides), https://www.beyondpesticides.org/resources/safety-source-on-pesticide-providers/what-is-integrated-pest-management
“Insect Pollinator Best Management Practices for Minnesota Yards and Gardens,” Minn. Dept. of Agriculture, https://www.mda.state.mn.us/sites/default/files/inline-files/pollinatoryardbmps.pdf
Factsheet: Neem Oil, National Pesticide Information Center, http://npic.orst.edu/factsheets/neemgen.html
“Planning a Companion Vegetable Garden,” https://www.gardeningknowhow.com/edible/vegetables/vgen/companion-vegetable-garden.htm