Cottonwood Borer: All You Need to Know for Healthy Trees

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The Cottonwood Borer is a large black and white longhorn beetle that can grow up to nearly 2 inches in length. Known to primarily infest cottonwood trees, these pests also target poplars and willows, causing significant damage to their hosts. Female Cottonwood Borers lay their eggs at the base of these trees in August, and the larvae bore into the tree as they grow.

As the larvae mature, they tunnel around the crown and buttress roots of the tree, creating galleries at and below the soil line. These tunnels can range from 2 to 3-inch diameter oval areas to 8 inches in length, depending on the tree’s size and infestation site. The damage caused by these pests can be detrimental to young trees, as their bark can be hollowed, partially severed, or girdled at or slightly below the root collar.

It’s essential to identify and manage Cottonwood Borer infestations early on, as they can cause irreversible damage to trees. Recognizing the signs of their presence and understanding their life cycle will help ensure the health and longevity of your cottonwood, poplar, or willow trees.

Cottonwood Borer Basics

Identification of Plectrodera Scalator

The Cottonwood Borer (Plectrodera scalator) is a type of longhorned beetle. It has a distinct black and white color pattern, measuring 1 1/4 to 1 1/2 inches in length. Notably, the larva is a large, white, deeply segmented grub, reaching 1 3/4 to 2 inches long when fully grown1. Here are the key features:

  • Color: Black and white
  • Adult size: 1 1/4 to 1 1/2 inches
  • Larva size: 1 3/4 to 2 inches

Distribution in the United States

Cottonwood Borers are found predominantly in the United States, infesting cottonwood, poplars, and willows2. Their larvae feed on tree trunks, causing damage, especially to young trees3.

Below is a comparison table of the trees cottonwood borer targets:

Tree Type Susceptibility to Cottonwood Borer
Cottonwood High
Poplars High
Willows High

Physical Characteristics

Distinguishing Adult Beetles

The Cottonwood Borer is a large longhorn beetle that measures about 1 1/4 to 1 1/2 inches in length. They have distinct coloration, featuring:

  • Black and white pattern on the body
  • Black antennae, as long or longer than the body
  • A robust appearance, with a large thorax

The black and white markings on their bodies are unique among longhorn beetles, making them easily recognizable. You can often find adult beetles on and around host plants during the summer.

Larvae and Pupae

Cottonwood Borer larvae are legless, roundheaded borers that grow up to 1.5 inches long. Their primary physical traits include:

  • Creamy white color
  • Deeply segmented body

Once the female lays eggs at the base of host plants, the larvae hatch and bore into the tree, causing most of the damage to the plant. During their pupal stage, they transform into adult beetles, eventually emerging to continue the life cycle.

Infestation and Damage

Host Trees and Damage Pattern

The Cottonwood Borer primarily targets cottonwood trees, but it also infests poplars and willows. Some common indicators of infestation include:

  • Larvae tunneling around the crown and buttress roots1
  • Galleries at and below the soil line, varying in length1

For example, a young cottonwood tree may showcase galleries that are 8 inches long, while an older or larger tree with an infestation site might display 2 to 3-inch diameter oval areas.

Impact on Tree Health

The health of the host trees might be impacted by the Cottonwood Borer in the following ways:

  • Adult feeding damages young trees2
  • Most damage is caused by larvae2
  • Young trees may be hollowed, partially severed, or girdled2

If a young tree experiences severe damage, it might break at or slightly below the root collar.

Life Cycle and Reproduction

Mating and Egg Laying

Cottonwood borers (Plectrodera scalator) are a species of longhorned beetles that infest cottonwood, poplars, and willows. Adults emerge from late May to early July and then begin mating. After fertilization, females oviposit, or lay eggs, in the bark crevices or soil near the base of host trees.

Larval Development

Once the eggs hatch, the larvae begin feeding on the tree’s inner bark and cambium layer, causing extensive damage known as girdling. During their development, the cottonwood borer larvae create galleries, which are tunnels they carve out within the tree or its roots.

Pupation and Adult Emergence

The cottonwood borer’s life cycle takes two years to complete. After a year of larval development, they pupate within their galleries in the second spring. New adults then chew their way out, leaving exit holes as they emerge.

Pros of cottonwood borers:

  • Some beetle collectors find them aesthetically appealing due to their large size and unique coloring.

Cons of cottonwood borers:

  • Cause significant damage to their host trees, potentially resulting in tree death.
  • Difficult to control, as they live within tree trunks and roots during most of their life cycle.

Comparison of two significant wood-boring insects:

Feature Cottonwood Borer Old House Borer
Order Coleoptera Coleoptera
Families Cerambycidae Cerambycidae
Host Trees Cottonwood, poplars, willows Primarily softwoods, e.g., pine, spruce
Damage Girdling, tree death Structural weakening of wood
Life Cycle 2 years 3-12 years

In summary, the cottonwood borer’s reproduction process involves mating, egg-laying by the females, larval development that lasts for about a year, and pupation in the second spring. The adult borers then emerge and leave exit holes in their host trees, marking the end of the life cycle.

Habits and Habitat

Preferred Conditions

The Cottonwood Borer (Plectrodera scalator) is a large, robust longhorn beetle belonging to the Cerambycidae family, commonly found in North America, particularly in the Great Plains and Rocky Mountain regions. They prefer sandy soils and are known to breed in the bases and roots of living trees like poplars, cottonwoods, and willows:

  • Poplar trees
  • Cottonwood trees
  • Willow trees

Sandy soils are especially favorable for the cottonwood borer’s habitat.

Expanding Range

The range of cottonwood borers has expanded over time due to several factors, such as climate change and the spread of host plants. These beetles can be found on and around their host plants during the summer, fulfilling their adult lifecycle responsibilities.

Seasonal Patterns

Cottonwood borers typically emerge around mid-May and can be seen during the warmer months of the year. They have a seasonality that affects their activity, and their predators, too, need to adapt and synchronize their behavioral patterns accordingly.

Throughout the cottonwood borer’s life, the majority of the damage is caused by its larval stage rather than the adult feeding stage. For instance, young trees can be hollowed, partially severed, or girdled at or slightly below the root collar, causing breakage and significant harm to the host plants.

Cottonwood Borers are an important aspect of North American ecology, and understanding their habits, habitat, and seasonal patterns provides us with valuable information to help manage their populations and protect our precious ecosystems.

Management and Control

Cultural Practices

Cultural practices can help prevent cottonwood borer infestation. These include:

  • Maintaining tree health: Proper cultivation, fertilization, watering, and thinning when necessary preserve high-value trees’ health1.
  • Eliminating debris: Removing infested, dead, or dying branches can reduce borer attraction and breeding opportunities1.

For example, in the U.S. South, cottonwood borers often cause destruction in nurseries, young plantations, and young natural stands on sandy soils2. Implementing healthy tree care and debris removal can mitigate their impact in these areas.

Chemical Treatments

Permethrin is a prevalent chemical treatment for managing cottonwood borer infestations3. However, it’s crucial to consider the pros and cons of using such treatments:

Pros:

  • Effectively kills the larvae and adult insects
  • Reduces the risk of further infestation

Cons:

  • Can harm beneficial insects and the environment
  • May not be suitable for all tree species or specific regions

Comparison of Cottonwood Borer and Ash Borer (Invasive Longhorned Beetles)

Feature Cottonwood Borer Ash Borer
Larval Stage Legless roundheaded borers, up to 1.5 inches long4 Larvae are cream-colored and flat, up to 1.2 inch
Host Trees Primarily cottonwood, but also poplars and willows5 Prefer ash trees
Infestation Effects Damage from larval tunneling, including hollowing, and girdling2 Damage by larval feeding, disrupting nutrient movement

In summary, managing and controlling cottonwood borer infestations requires a combination of cultural practices and chemical treatments. Remember to maintain tree health, remove debris and weigh the pros and cons of chemical treatments like permethrin.

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Footnotes

  1. Oklahoma State University 2 3 4 5
  2. Texas A&M University 2 3 4 5 6
  3. University of Kentucky 2
  4. University of Kentucky
  5. Texas A&M University

 

 

 

 

 

 

 

 

 

 

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Authors

  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

    View all posts
  • Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

    View all posts
Tags: Cottonwood Borer

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10 Comments. Leave new

  • layla pinell
    May 25, 2009 10:39 pm

    ….HAHA…WELL WE ARE @ THE BOTTOM OF THE BOOT & I HAVE SHOWN IT TO MANY PEOPLE & THEY HAVE NEVER SEEN 1….JUST YESTERDAY , ACTUALLY RIGHT AFTER I EMAILED YOU GUYS, MY HUSBAND YELLS FOR ME TO OUTSIDE…HE FOUND ANOTHER 1 BUT IT WASN’T BLACK & WHITE…BUT HAD THE SAME FEATURES BUT NOT THE SAME COLORS…..I DIDNT TAKE A PIC BUT I SHOULD HAVE……..

    Reply
  • Definitely a visually beautiful picture. I would love a bug calendar 🙂

    Reply
    • Dear TJOswego,
      We like the calendar photos to have a very quirky aesthetic. Keep that in mind when you pull out the camera. Though it is quite lovely, your photo of a Clavate Tortoise Beetle is more suited to a traditional guide book.

      Reply
  • You absolutely can use the picture. The reason for all of the bright colors is it’s on a class of 2010 plate since we were having a graduation party for my friend’s son. I’ve never seen these bugs down here before so it was too much of a great find to NOT snap a pic!

    Reply
    • Thanks Lindsay,
      We will have to look into the cost of this project before we seriously entertain publishing a calendar.

      Reply
  • Would love to purchase a calendar, especially of photos like this one! Would make a great gift for kids in my daughter’s class – especially for hard to buy for boys!

    Reply
  • Hi Bug Man

    I would like to see a bug calander (my godson would love it). Anyway……I am going to submit a really cool moth photo, as soon as I am done here. Thanks

    Reply
    • Thanks for your input. Doing a calendar might be a profitable way to learn the program In Design.

      Reply
  • We have just found a cottonwood borer on our cottonwood tree and my daughter deeply wants to keep it as a pet. Any tips on how to create a terrarium in which is could live happily?

    Reply

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