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Killing Squash Bugs: How To Identify and Control Anasa Tristis

In late summer, your pumpkin patch starts showing odd signs of wilt. It’s patchy at first, but you start noticing yellowed and darkened leaves, wilted vines, and you may actually start seeing young pumpkins start to turn yellow and die on the vine. Your zucchini plant’s starting to do the same. And worse, you’re seeing a lot of little black bugs, ones that are flat and which can flutter away at a moment’s notice.

These dreaded insects are likely to be the squash bug, Anasa tristis. And it’s imperative that you get these ravenous little parasites out of your garden before you are overwhelmed and lose your plants and your harvest!

Good Products to Eliminate Squash Bugs:

Squash Bug Overview

Common Name(s) Squash bug
Scientific Name(s) Anasa tristis
Family Coreidae
Origin Central America, the United States, southern Canada
Plants Affected Cucurbits such as squash, zucchini, pumpkin, gourds, watermelon, and cucumber
Common Remedies Handpick insects/nymphs/eggs. Use diatomaceous earth, neem oil, pyrethrin-based sprays. Floating row covers are effective at prevention. Grow varieties which are resistant.

Types of Squash Bugs

Squash vine borer
The squash vine borer. Source: Mean and Pinchy

The primary focus of this piece is on Anasa tristis, most commonly referred to as the squash bug. But another insect is often referred to as a squash bug as well. The squash vine borer (Melitta curcurbitae) also tends to favor cucurbits. It cannot be treated identically to Anasa tristis, as it’s a moth species with a caterpillar-like larval state, but the remedies utilized for squash bugs can have some effect nonetheless. For now, we’ll keep our focus on actual squash bugs, but be forewarned that if your insect foe has an adult moth form in black and red, you have a different fight on your hands!

Two squash bugs
Two squash bugs. Source: lfelliott

The squash bug (Anasa tristis) itself is a greyish-brown to brown-black insect, flat and shield-shaped in appearance and about a half-inch long. Often, it has a row of gold or brown dots along the outside of its abdomen. They often are dark enough in coloration that they appear to be small black bugs, but if looked at more closely, it’s a very dark brown. It can create an unpleasant aroma in large populations or when disturbed.

Life Cycle of Squash Bugs

Squash bug eggs
Squash bug eggs. Source: theloushe

The squash bug life cycle includes eggs, nymphal stages, and adulthood.

Egg laying begins as the weather warms up, somewhere between April and June in most areas. At that point, the adults emerge from their overwintering location and fly to their intended plant hosts. Depending on the climate, an adult female can lay anywhere from one to three clusters of eggs at a time. Each cluster is usually around eighteen eggs. The eggs are oval and tend towards a dark bronze color, and are laid on the underside of leaves.

Seven to nine days later, the eggs hatch into the first of five nymphal stages, or instars. In the first stage, the hatched nymphs are green and appear hairy, and they’re about a tenth of an inch in size. For each subsequent instar, the nymphs grow in size, gradually become darker, and lose their hairy spines. By the fifth instar, the nymph is just a little smaller than an adult, is starting to form wing pads, and has become a dark grey in color. The entire process from hatching to adulthood takes about 33 days.

Common Habitats for Squash Bugs

Like many insects, the habitat for squash bugs is generally around its food source. Since nymphs and adults feed on a wide variety of cucurbits, that’s usually where you’ll find them. Eggs will be on the underside of leaves, and the nymphs can be found along the leaves, stems, or fruit. The adults can be anywhere around the plant.

The most popular plant for squash bugs is usually pumpkin, and that is because on average, 70% of eggs laid on the pumpkin plant seem to live to maturity. This number gradually reduces in quantity with other plant types.

In addition, squash bugs overwinter as adults in sheltered places, such as in plant debris (dead leaves/vines) or rocks.

What Do Squash Bugs Eat?

I keep mentioning the cucurbits, but let me go into a bit more detail on the Cucurbitaceae family and what is most likely to fall victim to squash bugs. The Cucurbitaceae family includes all species of the gourd family, but isn’t limited to hard-shelled gourds. This family includes all varieties of pumpkin, squash, and zucchini; watermelon, calabash, honeydew, cantaloupe and other melons; cucumbers, miscellaneous gourds, and luffa.

Any of these can fall prey to the squash bugs, but their favorite is pumpkins. Other related squashes such as acorn, butternut, summer, winter, or related squash plants are at high risk, with the risk slowly minimizing as the family branches out into sweeter melons or fruits.

Squash bugs are doubly-dangerous because they are a carrier for Serratia marcescens, also known as cucurbit yellow vine disease or Anasa wilt. When they eat, they typically suck sap from the leaves and stems of the plant, but while doing so, they inject toxic venom into the plant itself. This can cause that part of the plant to wilt, darken in color, and die. Depending on the size of the infestation, it can be anywhere from just a small part of the plant to the whole plant that suffers squash bug damage.

How To Get Rid Of Squash Bugs

The best way to get rid of squash bugs is to never get them at all. But once you have them, you need to be proactive in eradicating them from your garden.

Handpick insects out of the garden, remove eggs from the underside of leaves, and drown them in a bucket of warm soapy water. This tactic works just fine until you get overwhelmed, and at that point, it’s time to look at other methods of controlling squash bugs.

Organic Squash Bug Control

Diatomaceous earth is a quick and effective means of control for squash bugs, although it is slightly less effective on the adults than it is on nymphs and eggs. Dusting this powder over all surfaces of the plants will greatly reduce the population of squash bugs and offers an effective means of squash bug control.

Neem oil is an effective squash bug insecticide as well. It coats the surface of the squash bug eggs, rendering them less likely to hatch, and will kill off nymphs and adults. Neem oil is also effective on diseases which can impact cucurbit plants such as powdery mildew, which makes it nearly essential in the home garden. It’s also non-harmful to pollinators, which is important if you want your plants to give you lots of produce!

Pyrethrin-based sprays are also quite effective at killing off the squash bug population. As pyrethrin sprays tend to linger on the plant a bit longer than neem oil, it’s best to use these sprays when you aren’t expecting to harvest any produce for at least a week or longer. This means they’re particularly useful in the younger stages of plant growth.

Environmental Squash Bug Control

Introducing parasitic insects into the garden which prey upon squash bugs is a very common control method.

One of the most commonly used is Trichopoda pennipes, a fly (about the size of an average housefly) which lays its eggs on adult squash bugs or nymphs. When the eggs hatch, the larvae burrow into the squash bug or nymph and consume it.

Other parasitic insects also attack squash bugs. The Hymenoptera order of parasitic wasps, especially the families Encyrtidae and Scelionidae, are particularly useful against not only squash bugs, but many other garden insects such as caterpillars and beetles.

Another way to control squash bugs is to offer alternative plant targets. To do this, plant varieties which are resistant to squash bugs in conjunction with a few sacrificial plants that aren’t resistant. The bugs will migrate towards the plants which do not have resistance, and can be easily contained and destroyed there instead of infesting the entire garden.

Finally, if you have seen squash bugs in your garden, try making a board trap. Take a few boards and lay them around the base of your plants. As squash bugs seek shelter at night, they will creep under the board. In the morning you can pick up the board and hand-pick the bugs out of the garden or knock them off the board and drown them in a bucket of soapy water.

Preventing Squash Bugs

The most effective way of preventing squash bugs, or any other adult flying insect such as cabbage worms or cabbage loopers, is to use a floating row cover. Using a Harvest-Guard floating cover keeps these insects from ever reaching your plants as long as it’s secured around to the soil around the plants thoroughly.

Growing plants that are naturally resistant to squash bugs is also a good preventative. Most varieties which are naturally resistant proudly proclaim it on their seed packets or informational cards at the nursery. While there is no total guarantee that they will be completely free from squash bug damage, it greatly reduces the likelihood of infestations.

Frequently Asked Questions

Q: Do any plants repel squash bugs?

A: Interestingly enough, yes! Catnip, also called catmint, tends to repel squash bugs. However, it might draw cats to your pumpkin patch or zucchini bed, so keep an eye out to make sure your cat isn’t rolling all over your plants. Dill also is considered to be effective, as is nasturtium and tansy. And finally, both peppermint and spearmint are considered effective natural repellents, but be careful with these, as mint plants also have the tendency to invade and take over if not controlled!

Q: Are squash bugs harmful to humans?

A: While the saliva of squash bugs can be toxic to plants, and can carry cucurbit yellow vine disease, their saliva is not harmful to humans, nor is any other part of the bug. However, they can and do stink when disturbed or squished. This means that if you have a sensitive nose, you might find the aroma offensive.

Q: Do preying mantises eat squash bugs?

A: They do, but preying mantises also eat ladybugs and other beneficial insects. If you have mantises in your garden already, they may assist you with the squash bug population somewhat, especially if you catch them and move them to where they’re most needed. But if you don’t already have preying mantises, don’t go running out to find some. It’s better to use the parasitic insects mentioned above which attack squash bugs and other pests, leaving beneficial insects alone.

All things considered, the last thing you want in amongst your butternut squash and zucchini plants, or flying towards your pumpkins, are the dreaded squash bugs. Hopefully with this piece, I’ve helped you find ways of wiping this particularly-irritating pest from your patches. Have you been at war with the squash bugs this year? I know I have! Let me know in the comments how bad your battle has been!



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