When Are Squash Vine Borers Active? Unveiling Their Seasonal Patterns

Squash vine borers can be a real nuisance to gardeners and farmers trying to grow healthy squash plants. These pests can cause significant damage to your plants, but understanding when they’re most active can help you better protect your plants.

The adult squash vine borer is a daytime moth that looks like a wasp, with an orange abdomen and black spots source. Typically, they are most active during the mid to late June, coinciding with the early growth stages of your squash plants. The moths lay their eggs on the stems of susceptible plants throughout the day, and once these eggs hatch, the larvae burrow into the stem and start feeding source.

Being aware of squash vine borer activity, you can take preventive measures and reduce the impact these pests have on your plants. Keep a close eye on your squash plants during the borer’s active season and consider using effective insecticides if necessary source. With diligent care and timely action, you’ll increase the chances of having a healthy and productive squash harvest.

Life Cycle of Squash Vine Borers

Egg Stage

During the egg stage, female squash vine borers (Melittia cucurbitae) lay flat, brown eggs on stems or leaves of squash plants. The eggs typically hatch in about 7 to 10 days. This is the beginning of their life cycle.

Larva Stage

Once the eggs hatch, the larvae emerge and immediately start to feed. They bore into the stem through a vertical slit, causing damage to the plant. As they feed, they produce frass, which is a mixture of feces and plant debris. This is a sign that your squash plant is infested with squash vine borer larvae.

Inside the stem, the larvae grow and develop. They could cause the plant to wilt, as their feeding restricts the flow of water and nutrients. This larva stage lasts for about 4 to 6 weeks.

Pupa Stage

After the larva stage, the squash vine borer transitions into the pupa stage. They create tough, dirt-covered cocoons in the soil near the base of the plant. They can overwinter in the soil, either as full-grown larvae or pupae, waiting for the next season to emerge as adult moths.

Adult Stage

Adult moths emerge from their pupae in late spring or early summer. They have a unique appearance, with clear wings and an orange abdomen with black spots. The metallic green, clear wings resemble those of wasps or bees, which helps protect them from predators.

During the day, adult squash vine borers are active and mate. After mating, female moths are ready to lay eggs on squash plants, starting the life cycle all over again.

By understanding the life cycle of squash vine borers, you can better monitor and protect your squash plants from this damaging pest. Remember to keep a lookout for signs of infestation and take action to prevent or control it.

Infestation Signs and Damage

Wilting of Plants

If you notice your squash plants wilting, this may be a sign of squash vine borer activity. The wilting is a result of the borers feeding on the inside of the stems, which disrupts water flow. To confirm their presence, check for a small hole near the base of the stem.

Sawdust-Like Frass

Another tell-tale sign of squash vine borer infestation is the presence of a sawdust-like substance, called frass, around the base of your plant’s stems. This frass is a mixture of chewed plant material and caterpillar waste. If you see this, it’s time to take action.

Damage to Cucurbit Crops

Squash vine borers are not partial to just one type of cucurbit crop. They damage a range of vine crops such as:

  • Squash (both summer and winter varieties)
  • Pumpkin
  • Cucumber
  • Melon

However, some cucurbits like butternut squash and acorn squash show more resistance to squash vine borer damage. Keep in mind that developing fruit on affected plants may also show signs of damage or reduced quality due to the borers’ activities. Overall, vigilance and early intervention are key to maintaining a healthy and productive garden.

Host Plants and Preferred Habitat

Squash as a Major Host

Squash vine borers are most active during mid-to-late June, and their moth flight continues until mid-August. They lay their eggs on the stems of squash plants, making squash a major host for these pests. The larvae feed on the plant’s roots and inside the stem, causing significant damage.

Squash vine borers prefer certain types of squash more than others. For example, they seem to target zucchini, summer squash, pumpkins, and certain winter squash more frequently.

Other Cucurbit Plants as Hosts

In addition to squash, squash vine borers could potentially lay their eggs on other cucurbit plants, including:

  • Butternut squash
  • Acorn squash
  • Cucumber
  • Melon
  • Gourd

However, the level of susceptibility among these host plants varies. According to Wisconsin Horticulture, there are differences in the susceptibility of various cucurbit plants to squash vine borer infestations.

Plant Susceptibility to Squash Vine Borer
Zucchini High
Summer Squash High
Pumpkin High
Butternut Moderate
Acorn Squash Moderate
Cucumber Low
Melon Low
Gourd Low

Remember, knowing the preferred habitat and host plants for squash vine borers helps you identify potential infestations and develop better prevention strategies. By focusing on the most susceptible plants in your garden, you can provide them with increased attention and protection, ensuring a successful harvest season.

Prevention and Control Measures

Cultural Control Methods

To control squash vine borers, start with preventive measures. One simple approach is crop rotation. By planting squash in a different location each year, you can reduce the likelihood of a borer infestation.

Another technique is using physical barriers. For example, wrapping the base of the plant’s stem with aluminum foil can prevent adult borer moths from laying eggs.

Biological Control Methods

Incorporating integrated pest management (IPM) strategies can help control squash vine borers. Some IPM methods include:

  • Attracting beneficial insects, such as wasps, that feed on borer larvae
  • Introducing beneficial nematodes that parasitize borer larvae
  • Encouraging birds in your garden, as they can eat borer moths and larvae

Chemical Control Methods

When other methods aren’t effective, consider using pesticides. However, it’s crucial to use these chemicals responsibly. Here are some recommended pesticides for squash vine borer control:

Pesticide Pros Cons
Spinosad Organic; low toxicity to beneficial insects Short residual activity
Carbaryl Broad-spectrum control Harmful to beneficial insects
Permethrin Long-lasting residual activity Toxic to aquatic life
Bifenthrin Low application rates; broad-spectrum control Highly toxic to bees and aquatic life
Esfenvalerate Fast-acting Limited residual activity
Bacillus thuringiensis (Bt) Organic; specific to caterpillar pests Requires consistent reapplication

Choose the appropriate pesticide based on your specific needs and always follow the label instructions for safe application.

Monitoring and Trapping Squash Vine Borers

Use of Pheromone Traps

Pheromone traps are an effective method for monitoring squash vine borers. These traps use synthetic chemicals to mimic the scent of female moths, attracting male moths. By placing a few of these traps around your garden, you’ll be able to detect the presence of adult borers. The main pros and cons of using pheromone traps include:

Pros:

  • Easy to set up and use
  • Good for monitoring borer population

Cons:

  • Usually only attract male borer moths
  • Won’t eliminate the entire population

Adult squash vine borers have clear wings and metallic green bodies, with an orange color and black dots. Their wingspan is around 1 inch.

Visual Monitoring

You can also visually monitor for squash vine borers by inspecting your plants regularly. Look for small, copper-colored eggs on plant stems, and for signs of damage, like wilting leaves or sawdust-like frass at the base of the stem.

In case you find a borer inside the plant, you can carefully remove it using a knife and cover the wound with soil to promote supplemental rooting.

Physical Trapping

Physical trapping involves using barriers or other methods to prevent borers from reaching your plants. Some examples include:

  • Wrapping the base of the plant stem with aluminum foil or cloth to protect it from egg-laying moths
  • Placing sticky traps near your garden to catch adult moths

Remember to be vigilant and persistent with your monitoring and trapping efforts to keep your squash plants healthy and free from squash vine borers.

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Squash Vine Borer

 

On my pumkin plants.
July 20, 2009
Took this pic July 16th. This guy didn’t seem very active, sat in this spot for about 2hrs. Preferred the shady side of the pumpkin leaves when he did move. I also have corn, hops, and gourds growing in the same area. It’s probably as common as dirt, but I can’t find it in my guides and now my curiosity is up. Thank you for your help
Lousy amatuer.

Squash Vine Borer
Squash Vine Borer

Chardon, Ohio
Dear LA (we just couldn’t bring ourselves to call you by your signed name),
This is a Squash Vine Borer, Melittia cucurbitae, a clearwing moth in the family Sesiidae.  Moths in this family mimic wasps for protection.  The Squash Vine Borer female lays her eggs on the stems of squash, pumpkin and gourds, and the larvae bore into the stems of the plant, often causing considerable damage and crop loss.

Letter 2 – Squash Vine Borer

 

What is this
August 9, 2009
Seen this winged insect sitting on an oak leaf, it looked like it had fur on its hind legs.
 T. Dunn
N. Illinois

Squash Vine Borer
Squash Vine Borer

Dear T. Dunn,
This is a Clearwing Moth in the family Sesiidae.  This family is characterized by wasp mimicry of its members.  Your moth is a Squash Vine Borer, Melittia cucurbitae.  The larvae bore in the stems of squash, pumpkins and related plants.

Letter 3 – Squash Vine Borer

 

Terrifying Orange Hornet(?)
October 8, 2009
Hi Bugman-
I spotted two of these orange flyers today in my backyard garden in Austin, Texas. They were buzzing around my zucchini plant(hopefully pollinating it in the process). They seemed a lot more interested in the plant than in me, yet due to my wildly irrational fear of stinging insects, I was petrified. I only managed to get a few shots before the buzzed away for good. I tried to identify them online but haven’t had any luck. Any idea on the species?
John
Austin, Texas

Squash Vine Borer
Squash Vine Borer

Hi John,
This is not a hornet.  It is a moth that mimics a hornet for protection.  It is a Squash Vine Borer, and the larvae will bore in the stems of squash and pumpkin vines, causing the plants to wither.

Squash Vine Borer
Squash Vine Borer

Thank you so much for the heads up. Before I had only heard of the Squash Bug as a pest to look out for around my squash vine. After I got your email, I read up on the Vine Borer, went out in the garden and saw the telltale signs that of the borers inside. I did some surgery with a knife and tweezers and pulled out a big fat borer larva…it’s a fairly small plant so I’m hoping it was the only one. Thank you so much for your help, you’re a lifesaver! -John

Letter 4 – Squash Vine Borer

 

Red and Black Wasp unidentified
May 15, 2010
Hello, Bugman:
These wasps have been appearing in our garden since 2008. I cannot seem to identify it. We live in Minnesota, and this seems to be a newer species for us. It looks like a wasp, but is scarlet red with black markings down the center of its back. Is it possible that some wasp species turn red for some reason? Help!
SageGrasshopper
Twin Cities, Minnesota

Squash Vine Borer

Dear SageGrasshopper,
This is not a wasp, but rather, a moth that mimics a wasp.  It is a Squash Vine Borer, Melittia cucurbitae, one of the Clearwing Moths in the family Sesiidae.  The larvae are stem borers in squash, gourd and pumkin plants.  That information may be verified on BugGuide.

Squash Vine Borer

Letter 5 – Squash Vine Borer from Ontario

 

Subject:  Garden bug
Geographic location of the bug:  Guelph Ontario Canada
Date: 07/16/2022
Time: 01:15 PM EDT
Your letter to the bugman:  This guy was flying around cucumber and zucchini plants mid day in full hot sun
Very cool bug of sorts. Had no interest in us. Didn’t see stopping at any flower just leaf to leaf. Never landing long
How you want your letter signed:  Thanks!

Squash Vine Borer

This is a Squash Vine Borer, a moth that resembles a wasp  The female lays eggs on the stems of squash, pumpkins, melons and other curcurbits.  When the larvae hatch they bore into the stems, potentially killing the plants.

Letter 6 – Squash Vine Borers Mating

 

What is this bug?
I am typically pretty brave around bugs, but for some reason this one scared me. The first time I saw it I thought it might be a wasp, but after some research I believe it is some kind of fly. I am used to the various bettles and garden pests that come with growing a garden, but this is the first year I remember seeing these. I think it is also a fine addition to your “Bug Love” page. Please help with the identification.
Jamie

Hi Jamie,
Your mating Squash Vine Borers, Melittia cucurbitae, are wasp mimic moths.

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Squash Vine Borer

 

On my pumkin plants.
July 20, 2009
Took this pic July 16th. This guy didn’t seem very active, sat in this spot for about 2hrs. Preferred the shady side of the pumpkin leaves when he did move. I also have corn, hops, and gourds growing in the same area. It’s probably as common as dirt, but I can’t find it in my guides and now my curiosity is up. Thank you for your help
Lousy amatuer.

Squash Vine Borer
Squash Vine Borer

Chardon, Ohio
Dear LA (we just couldn’t bring ourselves to call you by your signed name),
This is a Squash Vine Borer, Melittia cucurbitae, a clearwing moth in the family Sesiidae.  Moths in this family mimic wasps for protection.  The Squash Vine Borer female lays her eggs on the stems of squash, pumpkin and gourds, and the larvae bore into the stems of the plant, often causing considerable damage and crop loss.

Letter 2 – Squash Vine Borer

 

What is this
August 9, 2009
Seen this winged insect sitting on an oak leaf, it looked like it had fur on its hind legs.
 T. Dunn
N. Illinois

Squash Vine Borer
Squash Vine Borer

Dear T. Dunn,
This is a Clearwing Moth in the family Sesiidae.  This family is characterized by wasp mimicry of its members.  Your moth is a Squash Vine Borer, Melittia cucurbitae.  The larvae bore in the stems of squash, pumpkins and related plants.

Letter 3 – Squash Vine Borer

 

Terrifying Orange Hornet(?)
October 8, 2009
Hi Bugman-
I spotted two of these orange flyers today in my backyard garden in Austin, Texas. They were buzzing around my zucchini plant(hopefully pollinating it in the process). They seemed a lot more interested in the plant than in me, yet due to my wildly irrational fear of stinging insects, I was petrified. I only managed to get a few shots before the buzzed away for good. I tried to identify them online but haven’t had any luck. Any idea on the species?
John
Austin, Texas

Squash Vine Borer
Squash Vine Borer

Hi John,
This is not a hornet.  It is a moth that mimics a hornet for protection.  It is a Squash Vine Borer, and the larvae will bore in the stems of squash and pumpkin vines, causing the plants to wither.

Squash Vine Borer
Squash Vine Borer

Thank you so much for the heads up. Before I had only heard of the Squash Bug as a pest to look out for around my squash vine. After I got your email, I read up on the Vine Borer, went out in the garden and saw the telltale signs that of the borers inside. I did some surgery with a knife and tweezers and pulled out a big fat borer larva…it’s a fairly small plant so I’m hoping it was the only one. Thank you so much for your help, you’re a lifesaver! -John

Letter 4 – Squash Vine Borer

 

Red and Black Wasp unidentified
May 15, 2010
Hello, Bugman:
These wasps have been appearing in our garden since 2008. I cannot seem to identify it. We live in Minnesota, and this seems to be a newer species for us. It looks like a wasp, but is scarlet red with black markings down the center of its back. Is it possible that some wasp species turn red for some reason? Help!
SageGrasshopper
Twin Cities, Minnesota

Squash Vine Borer

Dear SageGrasshopper,
This is not a wasp, but rather, a moth that mimics a wasp.  It is a Squash Vine Borer, Melittia cucurbitae, one of the Clearwing Moths in the family Sesiidae.  The larvae are stem borers in squash, gourd and pumkin plants.  That information may be verified on BugGuide.

Squash Vine Borer

Letter 5 – Squash Vine Borer from Ontario

 

Subject:  Garden bug
Geographic location of the bug:  Guelph Ontario Canada
Date: 07/16/2022
Time: 01:15 PM EDT
Your letter to the bugman:  This guy was flying around cucumber and zucchini plants mid day in full hot sun
Very cool bug of sorts. Had no interest in us. Didn’t see stopping at any flower just leaf to leaf. Never landing long
How you want your letter signed:  Thanks!

Squash Vine Borer

This is a Squash Vine Borer, a moth that resembles a wasp  The female lays eggs on the stems of squash, pumpkins, melons and other curcurbits.  When the larvae hatch they bore into the stems, potentially killing the plants.

Letter 6 – Squash Vine Borers Mating

 

What is this bug?
I am typically pretty brave around bugs, but for some reason this one scared me. The first time I saw it I thought it might be a wasp, but after some research I believe it is some kind of fly. I am used to the various bettles and garden pests that come with growing a garden, but this is the first year I remember seeing these. I think it is also a fine addition to your “Bug Love” page. Please help with the identification.
Jamie

Hi Jamie,
Your mating Squash Vine Borers, Melittia cucurbitae, are wasp mimic moths.

Authors

    by
  • 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.

  • Piyushi Dhir

    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.

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