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Mountain Pine Beetle Treatments & Pollinator Protection

A Message from the Evergreen Garden Club

Mountain pine beetles pose a real threat to pine forests throughout Colorado, including the Evergreen foothills. Property owners often turn to preventive chemical spraying to protect individual trees. However, many of the chemicals commonly used in mountain pine beetle treatments are highly toxic to pollinators, including over 900 native bee species (such as sweat, mason, and bumble bees), butterflies (swallowtails), and hummingbirds.

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Because Evergreen supports diverse pollinator populations that are essential for native plants, gardens, and local ecosystems, the Evergreen Garden Club encourages residents to understand the potential impacts of these treatments and to consider alternatives that reduce harm to beneficial insects.

Why Pollinator Safety Matters
 

Pollinators—including bees, butterflies, moths, beetles, and hummingbirds—play a vital role in both natural ecosystems and food production. Many plants in Colorado’s forests, meadows, and gardens depend on pollinators to reproduce.​

​Unfortunately, several insecticides used to prevent mountain pine beetle attacks are broad-spectrum pesticides, meaning they do not distinguish between pest insects and beneficial species. Research shows that:

  • Many pesticides drift or spread beyond their intended target, meaning over 90% may end up affecting non-target organisms. (bcn.boulder.co.us)

  • The commonly used insecticides carbaryl and permethrin are highly toxic to honeybees and other beneficial insects. (bcn.boulder.co.us)

  • Even short exposure to residues can harm pollinators, particularly if treatments coincide with active foraging periods. (UMass Amherst)

  • These chemicals may also impact aquatic insects and other wildlife if they enter water through runoff or drift. (UMass Amherst)

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Common Pine Beetle Treatment Methods

 

Professional tree services in Colorado typically offer the following preventive options for mountain pine beetle management.

​​Preventive Insecticide Sprays

Licensed arborists often apply insecticides to the trunk of healthy pine trees before beetle flight begins in summer. Typical active ingredients include:

  • Carbaryl

  • Permethrin

  • Bifenthrin


These sprays can effectively protect individual trees for one season when applied correctly. However, they are broad-spectrum insecticides that affect beneficial insects and are generally recommended only for high-value trees near homes or structures. (Colorado State Forest Service)

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Reducing Harm When Chemical Sprays Are Used

If chemical spraying is chosen, pollinator impacts can be reduced by following best practices:

  • Treat only high-value trees, not entire forested properties

  • Avoid spraying when nearby plants are flowering

  • Apply treatments when pollinators are least active (early morning or evening)​​

  • Pollinator protection guidelines strongly emphasize avoiding pesticide applications when bees are actively foraging. (Colorado Beekeepers Association

 

Work with licensed arborists who follow state pesticide regulations and best practices. Old Growth Tree Service, an Evergreen Garden Club Business Member is a great resource!

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Trunk Injection Treatments

Trunk injections deliver treatments directly into the tree’s vascular system, keeping the product contained within the tree and minimizing drift, runoff, or surface residues. This makes them one of the lowest-risk methods for pollinators (bees, butterflies, etc.) and birds (e.g., woodpeckers boring for insects or eating seeds), compared to sprays or soil applications. Benefits to this type of treatment include:

  • Negligible external exposure to flowers, pollen, or nectar in most cases

  • Minimal risk for wind-pollinated trees (e.g., ash, pine) or when applied post-bloom

  • Certain systemic insecticides (e.g., some neonicotinoids) can reach pollen/nectar in flowering trees like linden, but injections generally result in lower residues than alternatives

  • Non-neonicotinoid options (e.g., Emamectin Benzoate) and proper timing further reduce any potential impact and also provide up to 2-3 years of protection against beetle colonization.

 

Arboricultural sources and research emphasize that trunk injections support pollinator safety by limiting broader environmental impact, making them a preferred method in integrated plant health management when pollinator concerns exist.

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Pheromone Repellents (Verbenone)

Synthetic pheromone packets can be attached to trees to signal that the tree is already occupied by beetles, discouraging new attacks. Benefits of this method include:

  • Non-toxic to pollinators, people, and wildlife

  • Can be used in forested areas where chemical sprays are undesirable

  • Often used as part of integrated forest management

 

Studies have shown these repellents can significantly reduce beetle attacks when used early and in combination with other management strategies. (bcn.boulder.co.us)​​

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Scientific References on Pesticide Toxicity to Bees

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The following studies and reports provide credible evidence on how common pine beetle insecticides affect pollinators:
 

  • Carbaryl (Sevin®)

    • ​Toxicity: Highly toxic to honeybees and native bees.

    • Key finding: Direct exposure can cause acute mortality; residues on flowers can harm foraging bees.

    • Source: Xerces Society for Invertebrate Conservation, Pesticide Impacts on Pollinators, 2020.)
       

  • Permethrin (Broad-spectrum pyrethroid insecticide.)

    • Toxicity: Highly toxic to bees

    • Key Finding: Even small drift onto flowering plants can be lethal.

    • Source: United States Environmental Protection Agency, Ecological Risk Assessment for Permethrin, 2011.
       

  • Bifenthrin (Commonly used for pine beetle prevention sprays.)

    • Toxicity: Highly toxic under certain circumstances.

    • Key Finding: Can significantly impact pollinators if applied incorrectly or during bloom

    • Source: Colorado State University Extension, Managing Forest Insects and Diseases, 2021.

 

  • Emamectin Benzoate (Non-neonicotinoid Trunk Injection Treatments)

    • Toxicity: Low to minimal risk with proper application; contained delivery limits exposure.

    • Key Finding: Some systemic actives may reach pollen/nectar in bee-attractive trees, but injections typically yield lower residues than sprays. Non-neonic options and post-bloom timing reduce risk further. For birds (e.g., woodpeckers boring for insects or eating seeds), risk is minimal—treatments stay in vascular tissue with little surface residue or impact on live prey.

    • Source: CSU Extension and arboricultural guidelines on reduced wildlife exposure via systemic methods.

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  • Verbenone (Pheromone Repellents)

    • ​Toxicity: Non-toxic to bees and wildlife.

    • Key finding: Effective for beetle deterrence without harming pollinators.

    • Source: Colorado State Forest Service, Mountain Pine Beetle Management Guidelines, 2022.​

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Forest Thinning & Tree Health

Maintaining healthy, well-spaced forests is one of the most effective long-term solutions. Best practices include:

  • Removing overcrowded trees to improving airflow and sunlight

  • Reducing drought stress through proper watering

  • Removing infested trees promptly

 

These steps improve tree resilience and reduce conditions that allow beetles to spread rapidly.​​Solar Treatments for Infested WoodCut infested logs can be stacked and covered with plastic to create high temperatures that kill beetle larvae. (Colorado State Forest Service)

A Shared Responsibility

 

The forests surrounding Evergreen are one of the defining features of our mountain community. At the same time, the foothills are home to a rich diversity of pollinators—including native bees, butterflies, and hummingbirds—that play an essential role in sustaining gardens, wildflowers, and wildlife habitat. Addressing mountain pine beetle risks while protecting pollinators requires a community-wide approach. The Evergreen Garden Club encourages residents, local organizations, and tree care professionals to work together to promote responsible and environmentally mindful practices.

How Homeowners Can Help

Individual property owners can make a meaningful difference by:

  • Learning about different pine beetle management options

  • Protecting high-value trees while avoiding unnecessary spraying

  • Asking tree care providers about pollinator-safe practices

  • Supporting native pollinator habitat in gardens and landscapes

  • Staying informed about forest health in the foothill region

How Tree Care Professionals Can Help

Professional arborists and forestry companies are key partners in maintaining healthy forests. Pollinator-friendly practices may include:

  • Clear communication about the insecticides used in treatments

  • Offering lower-impact options such as non-neonicotinoid trunk injection treatments and verbenone pheromone repellents when appropriate

  • Applying treatments with careful post bloom timing and precision to minimize drift

  • Advising homeowners on forest health and integrated pest management strategies

Legal & Educational Disclaimer:  The information on this page is provided by the Evergreen Garden Club for educational purposes only.

  • The content is not intended as a substitute for professional advice.

  • Homeowners should consult licensed arborists, pest management professionals, or local authorities before applying any pesticide or implementing pest control measures.

  • The Evergreen Garden Club does not endorse specific products or companies and is not responsible for outcomes resulting from the use of any treatment described on this page.

  • Users assume all responsibility for actions taken based on the information provided.

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