The Squash Vine Borer (melittia cucurbitae) is one of the most significant pests (aka bad garden bugs) of squash, pumpkins, cucumbers and melon crops.
Although these squash bugs do not usually appear in great numbers, it only takes a few to do a lot of damage.
In this article, we will describe the Squash Vine Borer, explain its lifecycle and share information to help you cope with this destructive pest in your summer garden. Read on to learn more.
What Do Squash Vine Borers Look like?
Squash Vine Borer larvae are actually caterpillars, but they look like grubs.
Their bodies are white, and they have small, brown heads. These larvae are insects, but they have eight appendages.
Six are legs and two are extensions of the body known as prolegs.
You will very seldom see these caterpillars because they bore into squash vines immediately after hatching.
When these caterpillars pupate, they create a black, silk-lined case about two centimeters long. This can be found in the soil surrounding squash plants.
The pupae stay in the ground throughout the winter and emerge in the early summer as adults.
Adult Squash Vine Borers look like wasps. They are actually clear-winged moths with a wingspan ranging between 2 1/2 and 4 centimeters.
Their bodies are black and orange and often have ringed patterns just as wasps do. Their front wings are metallic green, and their back hind wings are clear with brown or black veins and margins.
It is easy to mistake these moths for wasps, not only because they look like wasps.
Also, because they fly during the day rather than at night when most moths are active. You can identify the moths by the loud buzzing sound they make as they fly.
When attempting to identify adult moths, you may feel a bit confused because you might not be able to see the back wings.
This is because the moths fold these wings while resting, so they cannot be seen.
What Is the Lifecycle of the Squash Vine Borer?
Female Squash Vine Borer moths lay eggs late in the summer. They usually lay single eggs at the base of a squash, pumpkin, melon or cucumber plant.
Occasionally, a female moth will lay a small cluster of two or three eggs, which are quite small. Each brown, flat egg is about the size of a pencil point.
It takes 7 to 10 days before the eggs hatch. As soon as they do, the larvae begin boring right into the stem of the host plant.
You can tell one of these larvae have entered your plant because you’ll see a small hole surrounded by what looks like sawdust.
This frass is a combination of the debris from the plant and also the droppings of the larva.
The larva spends about a month inside the stem of the plant. It tunnels its way through the stem eating everything in its path.
When it is time for the larva to pupate, it burrows down through the roots and a couple of inches into the soil to spin its cocoon.
In cold climates, these pests have one generation annually. In warmer climates, two generations are possible annually.
What Kind of Damage to Squash Vine Borers Do?
Tunneling through the stem of the plant does a great deal of damage and will kill the plant in a fairly short period of time.
Not only does the burrowing create physical injury to the plant, it also interferes with the plant’s ability to uptake nutrients.
This creates a blockage in the stem that prevents water from reaching the rest of the plant.
If left uninterrupted, borers cause plants to wilt, turn yellow, weaken and die.
As the stem breaks down, you may begin to see deposits of sawdust-like frass poking out of weakened and rotted areas on the main stem.
If the stem breaks down very quickly, borers may begin to eat the plant’s fruit.
Squash Vine Borer Damage: How To Tell If Plants Have Been Attacked
Watch for These 5 Signs and Symptoms:
At first, this may only occur when the sun is hot; however, as time passes and damage worsens the entire plant will collapse altogether.
Entrance Holes and Frass At The Base of the Plant
When you see entry holes filled with a greenish orange, sawdust-like substance, it’s a dead giveaway that your plant has been invaded by Squash Vine Borers.
Rotting at the Base of the Plant
The physical damage and the decomposition of the frass will cause the base of the stem to rot, become mushy and collapse.
As the plant starves, the leaves and stems will become yellow.
Fruits may begin to wither and rot both as a result of lack of nutrients and in the event the larvae begin consuming the fruit from the inside out.
How Can You Control Squash Vine Borers?
Use a combination of methods to deflect, discourage and kill both adults and larvae.
You may be able to prevent Squash Vine Borer adult females from laying eggs on your plants by setting up a physical barrier using aluminum foil or a paper cup as demonstrated in this video.
One simple way to reduce the numbers of Squash Vine Borers is to rotate your crops.
If you had summer squash in one field or one area one season, mix it up and plant something different there the next year or season.
Just make sure that your new crop is not another type of squash, cucumber or melon. Crop rotation interrupts the borer’s ability to complete its lifecycle.
Examine your plants frequently early in the growing season. If you see borer eggs, scrape them off.
If squash borers are already in your plants, you may have a good chance of controlling them if you can catch them early.
If you see that a Squash Vine Borer has made a hole in one of your plants, do a little surgery to locate and remove the offender. You can use a razor blade, sharp knife or something similar to make a small incision.
Dig the caterpillar out with the piece of wire or other sharp implement and then cover the damaged part of the stem with moist soil. This will help it to heal more quickly.
Turning your soil thoroughly before winter sets in will also help disrupt the lifecycle of the Squash Vine Borer.
Any pupae in the soil will be exposed to cold temperatures, sunlight and other elements that will kill them. Turn the soil again in the springtime before planting a new crop.
You could plant a small, very early crop of squash that the pests prefer, such as Blue Hubbard squash.
Allow this small crop to become infested while you happily plant your other crop elsewhere. When you’re sure that larva have overtaken your Blue Hubbard squash crop, pull it up out of the ground and burn it!
Block Moths’ Entry
You can place row covers over your squash, melon and cucumber plants early in the season when the moths are active. Be sure to remove them when flowers appear so that your plants can be properly pollinated.
Adult moths are attracted to yellow, so it is easy to trap them in a small yellow container with a few inches of water and little dish soap. Place these traps between your plants early in the summer and check them frequently.
Choose Crops Carefully
The larvae prefer some types of squash and melons over others. For example, they are less attracted to watermelons, melons, cucumbers and butternut squash than they are to yellow squash and zucchini.
Do Chemical Control Insecticides Work on Squash Borers?
If you’re going to use pesticides, you should use them very early in the season so that they will affect the adult moths before egg laying begins.
Place pesticides or natural deterrents at the base of plants for the greatest effectiveness.
Bacillus thuringiensis (Bt) may be effective against the caterpillars.
When applied at just the right time, during the very brief window between the hatching of the larva and its entrance into the plant stem.
Some gardeners report good results from injecting the stems of affected plants with Bt.
Use A Combination Of Methods To Discourage Squash Vine Borers
These pests are persistent, and no single method will work to eliminate them from your garden.
If you stay on your toes and practice good garden management by:
- Keeping the soil tilled
- Rotating crops
- Reducing the number of adult pests
- Keeping a sharp eye out for eggs and caterpillars
… you have a good chance of avoiding the damage wrought by Melittia cucurbitae aka squash vine borers.