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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 that are widely used in agriculture to protect plants from pests. Neonicotinoids are designed to paralyze and kill pests by overstimulating their central nervous system (Raichel, 2018). Canada has approved three neonicotinoids for use (clothianidin, imidacloprid, and thiamethoxam), which are sold as powder concentrates or as ingredients contained in foliar sprays (Health Canada, 2020).

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

In the United States, a major contributing factor to the recent population decline of the monarch butterfly has been the contamination of milkweed with toxic chemicals, such as 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, specifically clothianidin, has likely contributed to milkweed contamination and had a detrimental effect on monarch survivability. Clothianidin is a chemical that has the potential to seep into groundwater and be persistent in the soil in which milkweed grows. The study notes that toxic levels of this chemical have been found in milkweed leaves (Science Daily, 2020).

Neonicotinoids pose several other risks to monarch butterflies, for instance, a 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 impact the size, weight, and survival of monarch caterpillars. In fact, only a 36-hour exposure to clothianidin-treated food (1 part per billion) resulted in their stunted or reduced growth (Pecenka, 2015).

Monarch butterflies contribute to the health of the environment and the ecosystem. They are an important food source for small animals, such as mice, and birds and insects. They are also part of a group of pollinators responsible for helping over 80 percent of the world’s flowering plants to pollinate (United States Department of Agriculture, n.d.). At the same time, they are an indicator species for weather and climate change—the absence, presence, or change in their populations reflects environmental health. Despite that, researchers announced early in 2021 that monarch butterflies are close to extinction (Jepsen & Black, 2021).

Scientists are concerned that the reaction of monarch butterflies to neonicotinoids will result in significant environmental issues involving the ecosystem as a whole. A persistent decline in monarch butterfly populations will make it impossible to keep birds, small animals and insects in check. The food cycle will inevitably be impacted as well due to a lack of sufficient pollination (Mondo, 2016). Even more importantly, since monarch butterflies are an indicator species [1], reduced populations will make it difficult for ecologists to monitor environmental change.

But some scientists argue that factors other than neonicotinoids are behind reduced monarch butterfly populations. A common counter argument is that the decline is due to milkweed loss (rather than contamination) because of the use of an herbicide known as dicamba (Donley, 2018). A second counter argument is that global warming and changing climate conditions (rather than neonicotinoids) are to blame for milkweed toxicity (Louisiana State University, 2018). A third counterargument is that neonicotinoid insecticides do not effectively harm monarch caterpillars (Frank, 2020). The fourth and final argument is that 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 such as monarch butterflies to a different set of problems (e.g., inhospitable resting grounds during migration).

Government Initiatives

In 2014, the United States, Mexico, and Canada promised to take action to preserve monarch butterfly populations (Sitnick, 2014). They pledged to protect and restore habitat in the three nations and to restrict the use of herbicides and put an end to habitat loss in the United States and Canada (Sitnick, 2014). The countries were also urged to pursue actions recommended at the 2013 Monarch Butterfly International Symposium, including “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 USD3.2 million into growing more milkweed (Howard, 2015), but did little to control 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 to prevent further monarch population declines (McKenna, 2017). Nevertheless, a survey carried out by the National Commission of Protected Natural Areas of Mexico and the Mexico office of the World Wildlife Fund found that between 2018 and 2019 there had been a staggering 53 percent decrease in monarch butterfly populations (2020).

Grassroots Movements

In the last decade, there has also been an increase in grassroots efforts to prevent monarch butterfly declines. Several initiatives have been launched by scientists, farmers, and environmental protection groups, including Greenpeace, Conservation International, and the David Suzuki Foundation, to fight the uncontrolled use of neonicotinoids in regions frequented by monarch butterflies during migration. These environmental activists have taken a coordinated approach to plant more milkweed, create and maintain monarch habitats, and curb the use of pesticides. But despite their concerted efforts, the U.S. Fish and Wildlife Service announced on December 15, 2020, that the monarch has now become a candidate under the Endangered Species Act.


Monarch butterflies help scientists determine the overall health of the environment. That should be enough to make banning neonicotinoid-based products from the market a priority. Canada has prevented some uses of neonicotinoids (Health Canada, 2020), but an outright ban was rejected as recently as March 2021 (Johnson, 2021). A year before that, the United States had promised to implement measures that would reduce risks to pollinators, but it then noted that none of these measures will include the removal of neonicotinoids from the market (Erickson, 2020).

Some scientists have identified a link between the introduction of neonicotinoids in agricultural practices and monarch population declines. With the usual caveat that correlation does not imply causation, it is imperative that we increase our efforts to study this relationship.


[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.


1. Bargar, T. A. et al. (2020, March 10). Uptake and toxicity of clothianidin to monarch butterflies from milkweed consumption. PeerJ vol. 8 e8669. doi:10.7717/peerj.8669

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.

4. Erickson, B. E. (2020, February 3). Neonicotinoid pesticides can stay in the US market, EPA says. C&EN, Chemical, and Engineering News.

5. Health Canada. (2020, September 30). Update on the Neonicotinoid Pesticides. Government of Canada.

6. Howard, E. (2015, February 9). U.S. Government Pledges $3.2 Million for Monarch Conservation. Journey North: Tracking Migrations and Seasons.

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.

8. Johnson, K. (2021, April 1). The Sprout: Health Canada backs off proposed neonic ban. iPOLITICS.,of%20the%20two%20neonicotinoid%20pesticides.&text=Health%20Canada%20introduces%20new%20restrictions,two%20main%20neonics%20(Real%20Agriculture)

9. Kauffman, V. (2015, February 9). News Release: Service, Partners Launch Campaign to Save Monarch Butterfly, Engage Americans. U.S. Fish and Wildlife Service (USFWS).

10. Louisiana State University. (2018, April 3). Global warming can turn monarch butterflies' favorite food into poison. ScienceDaily.,plant%20food%20into%20a%20poison.

11. McKenna, C. (2017, February 9). Monarch Butterfly Numbers Dropping but Government Commitment Strong: McKenna. The Star.

12. Mondo, M. (2016). Of Monarchs & Milkweed. Sombrilla, the University of Texas at San Antonio Magazine.

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.,The%20survey%20found%20that%20the%20area%20of%20forest%20occupied%20by,(6.05%20hectares)%20of%20forest.

14. Pecenka, J.R., L., J.G. (2015, April 3). Non-target effects of clothianidin on monarch butterflies. The Science of Nature 102 (19), 1-5. doi:10.1007/s00114-015-1270-y

15. Raichel, D. (2018, November 9). 10 Things you Always Wanted to Know About Neonics. Natural Resources Defense Council (NRDC).

16. ScienceDaily. (2020, June 8). Milkweed, only food source for monarch caterpillars, ubiquitously contaminated: Harmful pesticides found in Western Monarch breeding ground. Science News.,-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).

18. United States Department of Agriculture. Animal Pollination. U.S. Forest Service.

19. U.S. Fish and Wildlife Service. (2021, January 26). Assessing the Status of the Monarch Butterfly. Monarch Butterfly.

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