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Monarch Butterflies in Decline: The Use of Neonicotinoids in Agricultural Practices

Written by Miranda A. Bocci

University of Toronto Graduate

Disclaimer: Please note that the views expressed below represent the opinions of the article's author. The following does not necessarily represent the views of Law & Order.

Neonicotinoids are a new group of pesticides derived from the chemical nicotine — which is widely used in agriculture to protect plants from pests. Neonicotinoids are designed to eliminate pests by acting on their central nervous system and paralyzing or killing host cells through overstimulation (Raichel, 2018). There are three neonicotinoids currently approved for use in Canada (Clothianidin, Thiamethoxam, and Imidacloprid), which are sold as powder concentrates for soil or as ingredients contained in foliar sprays (Health Canada, 2020).

The use of these pesticides in agricultural practices has led to a fierce debate among conservation groups and scientists over their environmental, climate, and human impacts. Some studies have concluded that the use of neonicotinoids affects the health and survival of birds, bees, earthworms, and other wildlife, and poses potential risks to mammals and humans (Wood, 2017). But additional studies need to be carried out on how these pesticides impact the monarch’s main food source — milkweed — a plant that grows in forests, fields, and wetlands.

Monarch butterflies contribute to the health of the environment and ecosystem. They are an important food source for small animals like mice, birds, and other insects and are part of a group of pollinators responsible for helping “over 80% of the world’s flowering plants to pollinate” (United States Department of Agriculture, n.d). But they are also an indicator species for weather and climate changes - the absence, presence, or change in their populations reflect environmental health. If monarch butterflies disappeared, the ecosystem as a whole might eventually collapse. Yet, despite the crucial role that the monarch butterfly plays in sustaining environmental health, researchers announced early in 2021 that monarch butterflies are now close to extinction (Jepsen, Black, 2021).

In the United States, a major contributing factor in the recent population decline of the monarch butterfly has been the contamination of milkweed with toxic chemicals, like neonicotinoids (Science Daily, 2020).

A 2015 study published in the journal Science of Nature, supports this argument by suggesting that the widespread use of pesticides containing neonicotinoids such as Clothianidin, has likely contributed to milkweed contamination and had a negative effect on monarch survivability. Clothianidin is a moderately soluble substance that has the potential to leach into groundwater and is highly persistent in the soil where milkweed grows. The study claims that toxic levels of this chemical have been found in milkweed leaves (Science Daily, 2020).

In addition, neonicotinoids pose several other risks to monarch butterflies, such as — a sudden collapse of migration and weakening of their immune system, leading to an inability to fend off viral and bacterial infections (Bargar, 2020). These chemicals have also been observed to negatively affect the size, weight, and survival of monarch caterpillars — resulting in stunted or reduced growth — after only a 36-hour exposure to clothianidin-treated food (1 part per billion) (Pecenka, 2015).

Scientists are concerned that the reaction of monarch butterflies to neonicotinoids will lead to larger environmental issues involving the ecosystem as a whole.

For example, a persistent decline of monarch butterfly populations will make it impossible to keep birds, small animals such as mice, and other insects in check. Additionally, the food cycle will be inevitably impacted due to a lack of sufficient pollination (Mondo, 2016). But more importantly, since monarch butterflies are an indicator species [1], reduced populations will make it hard for ecologists to monitor changes in the environment.

A common counter-argument to the impact of neonicotinoids is that the main cause of monarch population declines is milkweed loss (rather than contamination) due to the use of a herbicide known as Dicamba (Donley, 2018). A second counter-argument is that global warming and changing climate conditions (rather than neonicotinoids) are responsible for contributing to milkweed toxicity (Louisiana State University, 2018). Yet a third counter-argument is that neonicotinoid insecticides are unsuccessful in killing monarch caterpillars (Frank, 2020). And lastly, since neonicotinoids become diluted in plants, the treated plants do not contain the substance for very long (Frank, 2020). Some studies have even suggested that neonicotinoids are important for protecting against beetle infestations and disease-carrying aphids (Mathiesen, 2014) that would expose pollinators like monarch butterflies to a different set of problems (such as inhospitable resting grounds during migrations).

Government Initiatives

In 2014, the United States, Mexico, and Canada committed their nations to take action to preserve and safeguard monarch butterfly populations (Sitnick, 2014). They pledged to protect and restore habitat in all three nations, restricting the use of herbicides in the United States and Canada, and putting an end to habitat loss in both countries (Sitnick, 2014). The countries were urged to pursue actions recommended at the 2013 Monarch Butterfly International Symposium; actions included “providing tools and guidelines to inform monarch conservation efforts to safeguard monarch butterfly migration”, “supporting state and federal agricultural conservation programs”, and “decreasing harmful effects of insecticides by improving implementation of [IPM] [2] practices, limiting the use of neonicotinoids, […] and […] reducing off-target exposure” (Sitnick, 2014).

Shortly after the 2014 declaration, the American government promised to invest USD 3.2 million into growing more milkweed (Howard, 2015), but the country took little to no action in controlling the use of harmful pesticides containing neonicotinoids. In a somewhat predictable sequence of events, Canada’s former Environment and Climate Change Minister, Catherine McKenna, followed suit by promising to take steps to restore natural habitat and to prevent further monarch population declines (McKenna, 2017). But a survey carried out by the National Commission of Protected Natural Areas of Mexico and the Mexico office of World Wildlife Fund (WWF) in 2020, found that in the 2018-2019 period there had been a staggering 53 percent decrease in monarch butterfly populations (National Commission of Protected Natural Areas of Mexico, 2020).

Grassroots Movements

In the last decade, grassroots efforts to prevent monarch butterfly population declines have intensified. Several initiatives were launched by scientists, farmers, and environmental protection groups such as Greenpeace, Conservation International, and the David Suzuki Foundation to battle the uncontrolled use of neonicotinoids on regions frequented by monarch butterflies during their migrations.

A coordinated approach has been used by these environmental activists to plant more milkweed, create and maintain monarch habitats, and curb the use of pesticides.

Yet despite their concerted efforts, the U.S. Fish and Wildlife Service (USFWS) announced on December 15, 2020, that “the monarch is now a candidate under the Endangered Species Act” (U.S. Fish and Wildlife Service, 2021). The agency had previously stated that as of the early 1990s, nearly one billion monarchs have disappeared (Kauffman, 2015).

That is a significant loss, which directly affects the larger food chain. But the introduction of neonicotinoids in agricultural practices in the last few decades has not only meant changes to the food chain but has also coincided with a period during which monarch butterfly populations actually began to decline. With the usual caveat that correlation does not imply causation, we might otherwise agree that this is usually a good starting point in determining a possible causal relationship between two given variables. It is, therefore, critical that conservation groups and scientists amp up their efforts to study this relationship.

Some suggestions are a) ruling out the possibility that milkweed loss or lack of access to it might be the cause of declining monarch populations; b) looking into possible sources other than global warming and climate conditions that might explain milkweed toxicity; c) carrying out further research and evaluations on the particular effects of neonicotinoids on monarch caterpillars; d) investigating how even brief exposures to neonicotinoids might contaminate milkweed; and, e) rethinking whether the assumed benefits of neonicotinoid-based products in agriculture truly outweigh the larger associated environmental costs. If these explorations prove to be unsuccessful in reversing the damage that has already been done, they will have at least assisted in responding to the potential extinction of monarch butterflies.


Similar to other pollinators, monarch butterfly populations help scientists to determine the overall health of the environment. However, in the last two decades, their populations have seen a 90 percent decline (Kauffman, 2015), a trend that might soon become irreversible without a complete ban of neonicotinoid-based products from the market. Canada has taken action to halt some uses of neonicotinoids (Health Canada, 2020), but an outright ban was rejected, as recently as March 2021 (Johnson, 2021). A year before that, Canada’s big sister had promised to implement measures that will reduce risks to pollinators, but it is advised that none of these measures will include the removal of neonicotinoids from the American market (Erickson, 2020).

These countries’ message is clear: neonicotinoids will not leave the market, even if that means that a contributor to the sustainability of the whole ecosystem will continue to face an uncertain future.

[1] Monarch butterflies react quickly to the slightest changes in the environment, so their presence/absence is often a good indicator of the health of the ecosystem. They are considered by scientists to be an indicator species of air pollution, habitat deterioration, and climate change.

[2] Integrated Pest Management (IPM) practices are the strategies used to prevent pests or their damage through a combination of mechanical/physical, biological, cultural, and chemical measures.


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2. Donley, N. (2018, March). A Menace to Monarchs: Drift-prone Dicamba Poses a Dangerous New Threat to Monarch Butterflies. Center for Biological Diversity, 1-17.


3. Dr. Frank, S. (Updated on 2020, May 4). Will Neonicotinoids on Milkweed Hurt Monarchs? Entomology – Insect Biology and Management. https://entomology.ces.ncsu.edu/2017/05/will-neonicotinoids-on-milkweed-hurt-monarchs/

4. Erickson, B. E. (2020, February 3). Neonicotinoid pesticides can stay in the US market, EPA says. C&EN, Chemical, and Engineering News. https://cen.acs.org/environment/pesticides/Neonicotinoid-pesticides-stay-US-market/98/web/2020/02

5. Health Canada. (2020, September 30). Update on the Neonicotinoid Pesticides. Government of Canada. https://www.canada.ca/en/health-canada/services/consumer-product-safety/reports-publications/pesticides-pest-management/fact-sheets-other-resources/update-neonicotinoid-pesticides-2020.html

6. Howard, E. (2015, February 9). U.S. Government Pledges $3.2 Million for Monarch Conservation. Journey North: Tracking Migrations and Seasons. https://journeynorth.org/monarch/spring2015/update_monarch_funding.html

7. Jepsen,S., Black S. H. (2021, January 19). Western Monarch Population Closer to Extinction: Still no Federal or State Protection in Sight. Xerces Society. https://xerces.org/press/western-monarch-population-closer-to-extinction-still-no-federal-or-state-protection-in-sight

8. Johnson, K. (2021, April 1). The Sprout: Health Canada backs off proposed neonic ban. iPOLITICS. https://ipolitics.ca/2021/04/01/the-sprout-health-canada-backs-off-proposed-neonic-ban/#:~:text=The%20Canadian%20government%20will%20limit,of%20the%20two%20neonicotinoid%20pesticides.&text=Health%20Canada%20introduces%20new%20restrictions,two%20main%20neonics%20(Real%20Agriculture)

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11. McKenna, C. (2017, February 9). Monarch Butterfly Numbers Dropping but Government Commitment Strong: McKenna. The Star. https://www.thestar.com/opinion/commentary/2017/02/09/committed-to-protecting-the-magnificent-monarch-butterfly-mckenna.html

12. Mondo, M. (2016). Of Monarchs & Milkweed. Sombrilla, the University of Texas at San Antonio Magazine. https://www.utsa.edu/sombrilla/spring2016/story/feature-monarch.html

13. National Commission of Protected Natural Areas of Mexico et al. (2020, March 20). Area of Forest Occupied by the Colonies of Monarch Butterflies in Mexico During the Hibernation Season of 2019-2020. WWF-Mexico News Release, 1-5. https://news.mongabay.com/2020/03/number-of-monarch-butterflies-wintering-in-mexico-down-by-more-than-half/#:~:text=monarch%20butterfly%20population.-,The%20survey%20found%20that%20the%20area%20of%20forest%20occupied%20by,(6.05%20hectares)%20of%20forest.

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15. Raichel, D. (2018, November 9). 10 Things you Always Wanted to Know About Neonics. Natural Resources Defense Council (NRDC). https://www.nrdc.org/experts/daniel-raichel/ten-things-you-always-wanted-know-about-neonics

16. ScienceDaily. (2020, June 8). Milkweed, only food source for monarch caterpillars, ubiquitously contaminated: Harmful pesticides found in Western Monarch breeding ground. Science News. https://www.sciencedaily.com/releases/2020/06/200608163451.htm#:~:text=Harmful%20pesticides%20found%20in%20Western%20Monarch%20breeding%20ground,-Date%3A%20June%208&text=Summary%3A,monarch%20butterflies%20in%20the%20west.&text=32%25%20of%20the%20samples%20contained,according%20to%20a%20new%20study.

17. Sitnick, J. (2014, February 20). WWF: North American Leaders Rightly Commit to Protecting Monarch Butterfly Migration. Make Way for Monarchs (MWFM). https://makewayformonarchs.org/2014/02/wwf-north-american-leaders-rightly-commit-to-protecting-monarch-butterfly-migration/

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