The impacts of neonicotinoid active ingredients, which are labelled for use against insect pests of trees and shrubs, on honeybees (Apis mellifera), in particular, are discussed below. Additional reasons for honeybee decline are also explored in this document. Steps professionals can take to support Massachusetts pollinators, as well as active ingredient alternatives to neonicotinoids are outlined below.
Neonicotinoids and Honeybees
Neonicotinoids were developed in the 1990’s due to increasing issues with insecticide resistance seen with older pesticides. Insecticide resistance is defined by the Insecticide Resistance Action Committee (IRAC) as: “a heritable change in the sensitivity of a pest population that is reflected in the repeated failure of a product to achieve the expected level of control when used according to the label recommendations for that pest species.” At the time, neonicotinoids were seen as an attractive option for multiple reasons, including:
- Relatively low mammalian toxicity. (Especially when compared to carbamates and organophosphates.)
- Persistence. (This can be a benefit when managing insect pests throughout a season/multiple years; however, it can also be a detriment when considering environmental risks.)
- Systemic action. (This can be a benefit when managing insect pests as neonicotinoid active ingredients can be sprayed on foliage, applied as soil drenches, trunk injections, or sprayed on the bark of trees and move throughout the tissues of the plant. Due to their high water solubility, a potential detriment can include leaching into the nearby environment, which is possible under certain conditions. Pertinent to the topic at hand, another potential cost of the systemic quality of neonicotinoids is that they can end up in plant pollen and nectar.)
Neonicotinoid active ingredients for tree and shrub insect management include: acetamiprid, clothianidin, dinotefuran, imidacloprid, and thiamethoxam. This class of insecticides is now under scrutiny by the scientific community and the public due to their ability to persist in the environment, high water solubility which may lead to leaching into unintended areas (under certain conditions), toxicity to pollinators such as honeybees and bumblebees, and findings suggesting that even as these chemicals degrade, they may remain toxic to bees and other pollinators. Not all neonicotinoids are created equal, however. Due to differences in their chemical structure, imidacloprid, thiamethoxam, and clothianidin are generally more toxic to bees than active ingredients such as acetamiprid (1,000 times less toxic than those mentioned previously). This difference is so much so that the Environmental Protection Agency has classified acetamiprid as a Reduced Risk insecticide. That said, neonicotinoid active ingredients are lethal to pollinators such as honeybees and bumblebees exposed to direct treatment or as residues on blooming crops, plants, or weeds. Exposure of pollinators to these active ingredients is often prohibited on product labels. Due to their systemic nature, neonicotinoids have also been detected in the nectar and pollen of treated plants, which can lead to honeybee and other pollinator exposure.
Laboratory studies investigating the chronic impacts of neonicotinoids on honey bees have found the following. Keep in mind that there are studies that are in disagreement of these findings, yet overall neonicotinoids may have the following impacts on honey bees:
- Increased mortality
- Impaired feeding, movement, and foraging
- Altered learning and memory
- Reduced immunity/increased infection
Semi-field studies also support those items listed above in bold. Increased infection was seen only under semi-field conditions, however, and not reported in laboratory studies.
Studies also suggest that neonicotinoids, when combined with exposure to other insecticides or fungicides, as well as certain pathogens, may increase the negative impact on pollinators such as honeybees.
Part of the current controversy with honeybees and neonicotinoids is because there have been different outcomes in studies conducted in the laboratory and semi-field conditions vs. those conducted under field conditions. The majority of studies conducted in the laboratory and semi-field conditions demonstrate that neonicotinoids are harmful to honeybees. Whereas under field conditions (situations you would expect honeybees to encounter in the “real world”), studies find limited or no effects on honeybees from neonicotinoids. These results are specifically for honeybees (Apis mellifera). When considering bumble bees, studies conducted in the lab, under semi-field, and field conditions are all more in agreement that neonicotinoids negatively impact those species. Bumble bees are considered to be 2-3 times more sensitive than the European honeybee to neonicotinoids, and they also suffer sub-lethal effects from these insecticides. Recent studies suggest that solitary bees may be even more sensitive to neonicotinoids than bumble bees.
Part of the difficulty with associating laboratory-based studies with what may be happening in the field is that honeybees are social insects and members of colonies or hives. They also forage on a huge variety of pollen and nectar resources. These social and behavioral complexities are very difficult to mimic in a lab setting.
Many of these studies focused primarily on imidacloprid (78%), followed by thiamethoxam (34%), clothianidin (33%), acetamiprid (19%), and dinotefuran (7%) (Lundin et al., 2015). Of the crop systems considered, most were in corn, followed by oilseed rape, and sunflower. There is a need for further study of the impact of neonicotinoid treatments on pollinators in uses such as home gardens and ornamental plants, including on trees and shrubs.
That said, multiple stressors are involved in pollinator declines and the issues faced by apiarists. In addition to pesticide use, there are multiple factors that have been identified as leading to a decline in pollinators (particularly honeybees) in the United States and elsewhere, including but not limited to:
- The introduction and spread of Varroa destructor, an external parasitic mite that attacks honeybees.
- Diseases such as those caused by certain viruses (Sacbrood), bacteria (American Foulbrood and European Foulbrood), fungi (Chalkbrood), and microsporidia (Nosema spp.).
- Pests such as wax moths and small hive beetles.
- Tracheal mite species such as Acarapis woodi.
- Side-effects of miticide use on hives for the management of mite pests.
- Increased urbanization.
- Reduced habitat and forage.
- Stress (ex. from transcontinental movement of hives, although this is not as well studied) and certain abiotic factors.
- Lack of genetic diversity.
- Exposure to pesticides.
*Items above in bold are often cited as of major significance.
Lundin, O., et al. (2015). “Neonicotinoid Insecticides and Their Impacts on Bees: A Systematic Review of Research Approaches
and Identification of Knowledge Gaps.” Plos One 10 (8): https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0136928
Pollinator Network @ Cornell: https://pollinator.cals.cornell.edu/threats-wild-and-managed-bees/pesticides/neonicotinoids/
How Professionals Can Support Massachusetts Pollinators
The following ways professionals can help support Massachusetts pollinators are outlined in the MA Department of Agricultural Resources, Massachusetts Pollinator Protection Plan, which is available online: https://www.mass.gov/files/documents/2017/06/zw/pollinator-plan.pdf
- Choose reduced-risk and least toxic insecticide options if chemical management of an insect pest is the only option available.
- If a neonicotinoid must be used, choose a reduced-risk option, such as acetamiprid, over active ingredients that have higher toxicity to bees (imidacloprid, thiamethoxam, and clothianidin). When using any neonicotinoid, use at the lowest possible label rate that is known to effectively manage the target pest (particularly on smaller plants, such as shrubs, whose biomass is smaller which may translate into higher concentrations of these active ingredients in pollen and nectar).
- Continue to practice Integrated Pest Management (IPM) techniques, which are beneficial not only for pollinators but also for the environment, the applicator, and non-target organisms.
- Follow label instructions for the safe and appropriate use of insecticides when they must be used. Certain practices can reduce the risk of exposing honeybees and other pollinators to applications, such as:
- Read, understand, and follow all label instructions regarding toxicity to bees.
- If necessary to apply insecticides, do so when bees are not actively foraging. This can change depending upon time of year and time of day.
- Do not treat trees and shrubs when they are in bloom.
- Be familiar with state regulations concerning the protection of pollinators.
- Minimize pesticide drift.
- Choose the least hazardous formulation of a pesticide.
- Plan applications appropriately, according to current weather conditions.
- Work with local beekeepers or beekeeping groups to ensure that you are aware of any locations of nearby hives, and notify beekeepers of upcoming pesticide applications in advance.
- Provide pollinator-friendly planting options, including annuals, perennials, shrubs, and trees.
- Encourage the expansion or construction of pollinator-friendly habitat where possible.
Massachusetts Core Supplement, November 2014, UMass Extension Pesticide Education Program:
Cowles, R.S. and B.D. Eitzer. 2017. Residues of neonicotinoid insecticides in pollen and nectar from model plants. J. Environ.
Active Ingredient Alternatives to Neonicotinoids
While some active ingredient alternatives to neonicotinoids exist for the management of certain arthropod pests, they may not all offer the same application methods as neonicotinoid insecticides. This may mean that if chemical management is necessary, but a client does not want to use neonicotinoids, a foliar spray may be the only method of application available as opposed to a trunk injection, basal bark application, or soil drench which can often be a practical, targeted means of application. When considering non-neonicotinoid options for the management of arthropod pests of trees and shrubs, remember that some of the organophosphate, carbamate, and pyrethroid alternatives also pose a risk to honeybees, other pollinators, wildlife, and non-target organisms.
The following list provides non-neonicotinoid alternatives for the management of insect and mite pests on trees and shrubs in the landscape without label warnings indicating “toxic or highly toxic to bees”:
*L = Landscape use; N = Nursery use listed if at least one product is registered for those uses in MA in those locations at the time this publication was drafted. If this document contradicts the product label, follow the product label. At least two different product labels, if available, were consulted for each active ingredient. Pests targeted and hazard levels represent multiple product examples.
To compare this to a more complete list of the insecticide active ingredients available for use on trees and shrubs, visit: https://ag.umass.edu/landscape/fact-sheets/tree-shrub-insecticide-active-ingredients-risks-to-pollinators-other-non