Gardeners know the importance of attracting more pollinators to their yards, but there are other beneficial insects that don’t get the attention and the credit they deserve, namely predatory and parasitoid insects. To discuss the value of these vital insects and how to attract them to your garden, my guest this week is horticulturist and author Jessica Walliser.
Jessica holds a degree in ornamental horticulture from The Pennsylvania State University and is an owner and co-founder of Savvy Gardening. She is the author of several books on gardening and the insects that reside in gardens, including “Good Bug, Bad Bug” and last year’s “Plant Partners: Science-Based Companion Planting Strategies for the Vegetable Garden.” This year, Jessica released the second edition of her book “Attracting Beneficial Bugs to Your Garden: A Natural Approach to Pest Control.”
Jessica lives northwest of Pittsburgh, Pennsylvania, and is currently the garden book editor for Cool Springs Press. She’s also a contributor to Fine Gardening, Urban Farm and Hobby Farms magazines, as well as a former contributing editor for Organic Gardening magazine and a former newspaper columnist and co-host of “The Organic Gardeners” on KDKA in Pittsburgh.
In all of her work, Jessica spreads the important message that insects are not the enemies of our gardens. Our gardens are an ecosystem, and insects are a valuable part of a healthy, functioning ecosystem that, in many cases, has the means to control pest populations without human intervention.
“If you’re trying to combat the pest in your vegetable garden, stop thinking of your vegetable garden as a vegetable garden,” Jessica advises. “Think of it as an ecosystem. It’s a place with many complex layers of organisms. from the tiny microscopic soil fungi all the way up to the groundhog that shows up and eats your plant. All of these things are interconnected. It’s a functioning ecosystem that we as gardeners have an exciting opportunity to nurture to create a good space for everybody that should live there.”
“Attracting Beneficial Bugs to Your Garden” book beautifully lays out what we should be planting to attract beneficial insects. Plant it, and they will come.
How Jessica Came to Appreciate Bugs
Jessica’s love of bugs came after she was long established as a horticulturist. When she wrote “Good Bug, Bad Bug” in 2008, she started to understand and appreciate the importance of all the little critters in our landscapes, and her interest snowballed from there. If she had a do-over, she would likely have become an entomologist rather than a horticulturist, she says.
In the one entomology class that Jessica took on the horticulture track, her professor said he didn’t want to fit the students into a mold of only learning about whiteflies on poinsettias. He wanted the students to do some critical thinking about bugs. The class would take field trips, including one memorable visit to a graveyard where the students learned how investigators can use bugs to solve crimes. Jessica found that entomology class fascinating, and that tiny spark in her would ignite a couple of years down the line.
In the introduction to “Attracting Beneficial Bugs to Your Garden,” Jessica candidly confesses to being a former bug hater. She explains that when she got out of college she worked for a landscaper and later started her own landscaping business. That meant her mission was to protect her clients’ plants. She would reach for a spray whenever she saw an aphid because she went into panic mode. But in time she made the journey to becoming a bug lover.
“The confession is that I’m not an entomologist, I’m just a horticulturist who is super keen on the insect world, and I love reading research,” Jessica says.
What Was Taken Out of ‘Attracting Beneficial Bugs to Your Garden’
Before getting into what additions were made to “Attracting Beneficial Bugs to Your Garden” between the first edition and the second edition, Jessica likes to highlight what was removed.
When the first edition was published in 2014, Jessica went on a speaking tour to botanic gardens and gardening organizations and she gave a lot of interviews about the book as well. She had expected that gardeners were interested in how they could plan and design a dedicated insectary border for the good bugs, much like a pollinator garden, but she found that was not the case. The gardeners she met didn’t want to create a new garden just for beneficial insects; they wanted to know how they can take the garden they already have and add the right plants and adopt the right practices and care techniques to make it a more welcoming environment for beneficial insects.
“They want to know how they can enhance what they already have rather than change or put something brand new in,” Jessica says.
A section with garden plans, maps, illustrations and plant lists was removed in the new edition because Jessica discovered that gardeners did not find it to be approachable or doable. So in the new edition, she addresses the question, “How do we make what we already have better for the bugs?”
Additions to ‘Attracting Beneficial Bugs to Your Garden’
In the eight years since the first edition of ‘Attracting Beneficial Bugs to Your Garden,’ there has been new research on native plants and how they impact beneficial insects in some really cool and fascinating ways, Jessica says. Scattered throughout the new edition are interviews with entomologists from throughout the world offering “a fascinating peek at their current research and things that we as garden people might not have thought about.”
One of the interviews is with Dr. Doug Tallamy of the University of Deleware. “I was able to include this great interview that connects native plants to beneficial insects in a way that surprised me, that I hadn’t thought of even after reading all of this research so that was a pretty exciting addition for me,” Jessica says.
Jessica notes that when we think about what to plant for beneficial predatory insects, we often think in terms of flowers that will supply nectar, which provides carbohydrates that many insects need to reproduce. She wondered if native plants have better nectar for native predatory insects, but Doug says that’s likely not the case. While some pollinators may require nectar that is a perfect match, for predatory insects, nectar is just nectar.
Doug explained that native plants are important to predatory insects for another reason: They host the insects that become prey for predators. For example, native oaks trees host sphinx moths, which are prey for Cotesia wasps. Having Cotesia wasps around your garden is a boon because they also prey on tomato and tobacco hornworms (which are also sphinx months).
“If you don’t have those trees around, you’re not going to have alternative hosts for those parasitic wasps,” Jessica says. “So when you get the tomato hornworms, the wasps aren’t going to be there.”
So in addition to all the flowers Jessica plants to attract predatory insects, she has many trees and a great diversity of plants around her landscape — not just in the vegetable garden — to support them. She calls it another layer of bricks in the foundation that good bugs need to stick around in your garden.
Aphids Are a Gift to Gardeners
Aphids are common garden pests that feed on ornamentals and vegetables alike, but Jessica points out how helpful an aphid infestation can be to gardeners. Think of aphids not as pests, but as resources for attracting beneficial insects, she says.
While gardeners typically hate to see aphids, it’s important to remember that aphid infestations are never severe enough to kill a plant. “In all my years of horticulture, I have never once seen a plant die from aphids infestation,” she says.
Aphids attract a variety of predatory insects to your garden, such as lady beetles, lacewings, syrphid flies, aphidius wasps, big-eyed bugs, and minute pirate bugs. “There’s just a ton, thousands — literally thousands — of species of beneficial predatory insects that use aphids as lunch,” Jessica says. “So when you have a lot of aphids, you have a lot of good bugs. And then when you have pests that really can kill plants, you’ve got all the predators right there and ready to roll.”
Let Mother Nature Do the Work
Jessica says everybody wants to know what they should spray, but in her experience and in the experience of many other horticulturalists, a pest is only really a problem when it’s an invasive, exotic insect that has no natural predators. She says if a pest is not a major problem, just chill out — your plants are going to be OK. She says you need to give Mother Nature time for the predators to show up and work their magic.
The Japanese beetle is an example of an invasive insect, but it has been in North America for so long at this point that there are now a group of predators that will eat it. And even when you have a big infestation of Japanese beetles on your blueberry plants or roses, it’s not going to kill your plant, Jessica says. The plant may not look great for the rest of the season, but it will survive.
An example of an invasive insect that will completely kill your plant is the emerald ash borer, an Asian jewel beetle first identified in the United States in 2002.
Some Good Insects Eat Other Good Insects
Scientists can learn what insects eat by “gut content analysis,” and the results can be surprising. It’s not always as simple as good bugs eating bad bugs. Sometimes good bugs eat other good bugs.
Many predatory insect species have a common source of food, such as the many predators that eat aphids. When one aphid predator eats a fellow aphid predator, it’s called intraguild predation.
Multicolored Asian lady beetles, though invasive, eat aphids and other pests, so they have benefits to farmers and gardeners. However, through gut content analysis, researchers have found that multicolored Asian lady beetles are also eating beneficial native North American ladybeetles.
Parasitic wasps — also known as parasitoid wasps because they kill their hosts — have parasites of their own. For example, a Cotesia wasp will lay eggs inside of a hornworm, the wasp larvae will eat the hornworm’s insides, and another parasitoid species may come along and lay its eggs inside the Cotesia wasp larvae.
‘Bug’ in Common Usage Vs. ‘Bug’ in Entomological Usage
“Bug” is a common term that the greater public uses for all of the creepy-crawlies out there, Jessica says, but not every creepy-crawly is a bug. For example, slugs may be called “bugs” but are really gastropods.
Insects are arthropods, which have exoskeletons. True bugs fall under the umbrella of insects. They belong to the order Hemiptera and have piercing-sucking mouthparts and six legs.
Spiders, ticks and mites are also arthropods, but they are not insects; they’re arachnids. Millipedes and centipedes are arthropods in the subphylum Myriapoda.
For the sake of ease, Jessica uses “bug” colloquially in her books and conversation.
Predators and Parasitoids
Jessica splits beneficial bugs into two categories: predators and parasitoids.
Predators are the beneficials that capture and eat their prey directly, like a lady beetle, spider or minute pirate bug. Parasitoids use prey to feed and house their developing young.
Parasitoids wasps and parasitoid flies either lay eggs directly inside prey or next to where prey is eating. In the latter case, a caterpillar ingests the eggs of a parasitoid, and those eggs hatch inside the caterpillar. In their larval stage, parasitoids consume and eventually kill their hosts. Amazingly, the larvae know to eat nonessential tissue first so their hosts live as long as possible.
When Cotesia wasp larvae inside of a hornworm are ready to pupate, they chew a tiny hole in the skin on the back of the hornworm and ooze their way out. Once on the outside of the hornworm, they spin white, rice-like cocoons. When they finish pupating, they pop out of the top of the cocoons as adults and fly off.
Purchasing Beneficial Insects
To tackle a persistent pest issue, you may want to speed things along by purchasing beneficial insects. This is called “introduced biocontrol,” wherein a grower brings in one organism to reduce the population of another organism.
Jessica has mixed feelings about introduced biocontrol. She knows that it is effective in greenhouses and other enclosed environments, but gardens are a different case. Thousands of insects released into a home garden at the same time likely won’t have the resources available to sustain their population.
“You have to have a heck of an aphid infestation in order to support the release of 4,000 larval lacewings in your garden,” Jessica points out.
If you are introducing beneficials that can fly away, there is no guarantee that they are going to stick around your garden.
Specialist predators, like the mealybug destroyer, will be more effective in a greenhouse that’s growing tropical plants than in a garden.
In the case of lady beetles that are sold for biocontrol, they are wild collected rather than raised in an insectory. Insects collected from the wild may have diseases that will spread when the insects are transported and sold, while insectory-raised insects are from a controlled, disease-free environment. Collecting native insects from the wild also has negative impacts on the ecosystems that they were removed from.
If you are going to purchase insects, Jessica suggests you buy them in their larval stage, before they grow wings and can fly away.
Larvae vs. Nymphs
For insects that go through a complete metamorphosis, such as caterpillars turning into butterflies or grubs turning into Japanese beetles, their juveniles are known as larvae, and larvae look nothing like the adult stage. For insects that go through incomplete metamorphosis, such as grasshoppers or squash bugs, they go from nymph to adult. The nymphs, though immature, look somewhat like the adults, and the nymphs go through four or five life stages called “instars.”
The Role of Nectar in Attracting Beneficial Insects
Most beneficial insects need nectar at some stage of their lives. To attract a variety of beneficial insects, you need flowers of various sizes.
A parasitoid wasp that lays an egg in the back of an aphid is super tiny — about the size of a gnat. Lady beetles, and particularly their larvae, are also rather small and lack the specialized mouthparts for eating nectar than butterflies have. “They can’t access nectar at the bottom of a deep, tubular flower,” Jessica says. “They’ll fall in there and drown.”
What small insects need are very shallow and exposed nectaries, which in many cases means tiny flowers. Think of flowers in the Apiaceae family (also known as the umbellifers) which include carrots, dill, parsley and similar species. Picture Queen Anne’s lace, which is a wild carrot. That big flower is not a single flower but rather an inflorescence that contains hundreds if not thousands of tiny flowers. Each tiny flower has a shallow exposed nectary that’s perfect for beneficial insects.
Asteraceae, the daisy family, is another example of a good nectar source for beneficials. Sunflowers, for instance, are daisies that have hundreds or thousands of flowers on their flower discs. (The petals around the disc are called “ray flowers.”) Coneflowers and cosmos also have flower discs.
Another place where beneficials can access nectar is called an extrafloral nectary. This is nectar made by certain plants from nectar-producing glands found someplace on the plant other than a flower. It might be at a node, which is where a leaf joins the stem, or it might be on the underside of a leaf. Scientists suspect that the nectar is a reward the plant offers to beneficial insects that protect it from pests.
Sunflowers, from the time they are very young, have extrafloral nectaries on the underside of their leaves. Elderberries and many members of the bean family also have extrafloral nectaries.
Animals and plants track the sequence of natural events, like the changing of the seasons, and they respond to these changes. This is called phenology. For her book, Jessica interviewed an entomologist on phenology as it relates to insects.
“Nature is way more predictable than we humans give it credit for,” Jessica says. “Things in nature happen in a certain sequence.”
For example, lilacs bloom at a certain time, and then a certain insect emerges from diapause (the insect version of hibernation). “The sequence of those events happens in a specific order,” she explains. “The timing of that sequence can change.”
Due to global climate change and the increase in the average temperature, that sequence is happening earlier and earlier on average. In some cases, climate change is disrupting the sequence and causing some events to decouple, with dire consequences.
If monarch butterflies begin their migration sooner or later than when milkweed is at its prime stage for monarch larvae, fewer larvae will survive to adulthood. The same can happen for predatory insects, such as big-eyed bugs waking up in the spring before their food sources are available.
By studying phenology, researchers have helped growers know when to expect the arrival of certain pests or when to expect certain plants to bloom. Researchers can create a timeline based on “degree days,” which is the number of days when the temperature has held above a critical temperature.
“It is a jaw-dropping science, and it is, I think, one of the best concrete ways that we can track climate change and the impact of how much warmer our climate is becoming on the pests and plants and what they do at particular times of the year,” Jessica says.
Some plants and insects respond to day length rather than temperature. If an insect responds to temperature when its food source responds to day length, decoupling can easily happen due to climate change. The insect will emerge and have nothing to eat.
This isn’t just a theory. “It’s happening,” Jessica says.
Sensible Ways We Can Help Insects
In addition to planting more natives and refraining from using pesticides, there are sensible ways that we can help beneficial insects.
Simply by leaving the leaves where they fall, we help insects. The leaves provide an insulating layer and hiding place for overwintering insects where they are less likely to be affected by freeze-thaw cycles.
Leaving herbaceous plants to stand all winter rather than cutting them back to the ground provides habitat where insects can crawl down and nest.
These little changes in our gardening practices can make a difference to more insects than we realize. “You’re talking about hundreds of thousands if not millions of insects that can be influenced just in your little tiny corner of the world,” Jessica says.
If we want to have a hand in improving the planet for insects, we can all start right where we live or garden, no matter how big or small.
How Climate Change Is Helping Pests Spread
Warmer temperatures are helping pests, particularly invasive pests, to spread their range. Jessica shares that she never had harlequin bugs in her garden in all her years of gardening, but in the last three years, this major pest of brassicas has arrived. The tobacco budworm and the leaf-footed bugs likewise showed up in Pennsylvania.
Certain insects may have been present in northern gardens but had only one generation per year. Now, those pests, such as cucumber beetles, are having two generations per year because the winter temperatures are not cold enough to kill them off.
I hope you enjoyed my conversation with Jessica Walliser. If you haven’t listened to our conversation yet, you can do so now by clicking the Play button on the green bar near the top of this post.
Have you witnessed predatory insects performing pest control in your garden? Let us know in the comments below.
Links & Resources
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“Attracting Beneficial Bugs to Your Garden” Second Edition by Jessica Walliser
“Plant Partners: Science-Based Companion Planting Strategies for the Vegetable Garden” by Jessica Walliser
“Gardener’s Guide to Compact Plants: Edibles and Ornamentals for Small-Space Gardening” by Jessica Walliser
“A Gardener’s Notebook: Life With My Garden” by Jessica Walliser and Doug Oster
“Good Bug Bad Bug: Who’s Who, What They Do, and How to Manage Them Organically” by Jessica Walliser
Ohio State University Phenology Calendar (for Ohio zip codes)
Disclosure: Some product links in this guide are affiliate links, which means we get a commission if you purchase. However, none of the prices of these resources have been increased to compensate us, and compensation is not an influencing factor on their inclusion here. The selection of all items featured in this post and podcast were based solely on merit and in no way influenced by any affiliate or financial incentive, or contractual relationship. At the time of this writing, Joe Lamp’l has professional relationships with the following companies who may have products included in this post and podcast: Rain Bird, Corona Tools, Milorganite, Soil3, Exmark, Greenhouse Megastore, High Mowing Organic Seeds, Territorial Seed Company, Wild Alaskan Seafood Box and TerraThrive. These companies are either Brand Partners of joegardener.com and/or advertise on our website. However, we receive no additional compensation from the sales or promotion of their product through this guide. The inclusion of any products mentioned within this post is entirely independent and exclusive of any relationship.