cultivating ‘good garden bugs,’ with dr. mary gardiner
HOW CAN YOU KILL this “bad” bug or that one? Well, here’s a thought that does not involve buying some packaged product with unintelligible ingredients on its label, or otherwise conducting an indiscriminate backyard assault: Make friends with a diversity of insects and other arthropods–the ones Ohio State University entomologist Dr. Mary Gardiner calls “natural enemies.”
Here’s the wrinkle, though: Most of us probably don’t know which ones those are, and in fact have misconceptions about who’s who–often deeply ingrained by fear or a visceral sense of creepiness about insects.
In her new book “Good Garden Bugs: Everything You Need to Know About Beneficial Predatory Insects,” Mary Gardiner (above and below) introduces us to a world of garden helpers, and she joined me on my public-radio show and podcast to do just that. Listen using the player below, or play the June 29, 2015 show at this link, or read along—or both. You can also enter to win the book, at the bottom of the page.
my good-bug q&a
with dr. mary gardiner
Q. So though it may seem obvious from the book’s title “Good Garden Bugs,” Mary, why do we want “natural enemies?” What was the goal for the book?
A. Natural enemies provide a very important service to gardeners by controlling pest insects. So these are insects that consume pest insects. There are both predators, which are foragers that find their own prey to consume, and also parasitoids, a unique type of natural enemy where the female adult will find a host for her offspring, and lay an egg either on or in that host, which will then develop as a larva and kill the host.
So between those two types of natural enemies, you can really find a large biodiversity of species within a backyard garden.
Q. So predators and parasitoids—and the parasitoids are sort of the stuff of science fiction movies, right? [Laughter.]
A. Several types of insects can live as parasitoids, but by far the most common are parasitoid wasps. They’re some of those wasps that you might see nectaring on flowers, with a very long part that looks like a stinger. People can often be quite fearful when they see something like that, but parasitoid wasps can’t sting humans.
What looks like a stinger is called their ovipositor [above, ovipositor on an ichneumon wasp on Margaret’s garden], and that’s used to inject an egg inside their host. Those wasps will look for pests like aphids or caterpillars to lay their eggs inside, and then the larvae lay their eggs inside that host, eating it from the inside out—so yes, a very alien-like existence.
Q. Sci-fi stuff! In the book you talk about three basic tactics for achieving “biological control”–for building up the populations of these natural enemies. What are they?
A. The first is importation biological control—and this is one that gardeners want to be aware of, but not that we’re going to take an active role in. That’s where an invasive pest is found in the United States—say the emerald ash borer, which many people have heard of. In order to control that invasive pest, scientists will go back to the native range of the pest to look for natural enemies, that they will bing back to the United States and then test for several years in controlled quarantine conditions.
If those natural enemies are deemed to be safe, and only attack their target hosts, then they will be released. So we might benefit from some of the services of these released natural enemies, but certainly not doing these releases ourselves.
Q. So that’s importation as a way to get some helpers.
A. Especially when some invasive insects are introduced, they’re introduced without their natural predators and parasitoids, and sometimes you can release one that’s host specific—it would be a parasitoid in almost all cases, because they are very host-specific—that would attack that host.
The second case is augmentation biological control. This is the one that I get the most questions about. In augmentation, periodic releases of natural enemies are made to increase the abundance of them in the natural environment. These are natural enemies that you can purchase online or in garden centers. They might be any kind of insect, like a predatory true bug, or a lady beetle, or a praying mantid that can be released in home gardens.
This is a way that people really see to manage insect pests, but really augmentation biological control is most successful within closed environments, like a greenhouse.
Q. Yes, exactly. It’s actually having tremendous results within the commercial greenhouse industry—plant wholesalers using it to reduce their chemical spray programs. It’s fascinating what’s going on with these releases within the confined environment.
A. If people have a small greenhouse or a hoophouse where they’re starting plants in the spring, this can be an effective strategy. If you notice mite or aphid issues, there are many biological controls that can be used.
But in the open garden, what I suggest people focus on is the third type of biological control: conservation biological control.
Q. I want to just ask more about the lady beetle—people buying pints of them. I really don’t get it.
A. There are several different species of lady beetle sold commercially. Some of those are reared in the lab, under controlled conditions, such as the mealy bug destroyer or the mite destroyer. Those lady beetles, if they’re native to your area, can be released and be very effective as we discussed in greenhouse conditions. But I wouldn’t suggest that people buy convergent lady beetles.
Convergent lady beetles are red lady beetles with black spots; they look like a typical lady beetle. They have two white converging bars on the top of their thorax. This is the most commonly sold lady beetle.
This is one of the only natural enemies that’s collected in the wild that I know of. It’s called the convergent lady beetle, and it actually converges in big aggregations to overwinter. Many of these collections are made in the Sierra Nevada Mountains in California. If people go out and collect these lady beetles and then sell them to biocontrol companies that distribute them.
There is no evidence that this is having a negative impact on their population, from that standpoint, but when you collect something from the wild it can have diseases, and its own pests with it, so we really don’t know the consequences of redistributing these lady beetles around the country.
Another reason not to release them, is when they come to in your garden, when they’re been taken from their winter aggregation, their tendency is to fly from where they think they were—the Sierra Mountains—and fly away into areas of agriculture. So they’re probably going to fly away out of your garden. So it’s not a very effective pest-management strategy to release them.
Q. Likewise, you brought up mantids—the praying mantis, as they are called—and people have a strong conception of either they’re very good, or very bad. But where do they fit—and are they even native insects? [Above, Carolina mantid.]
A. There are many different species of mantids across the U.S. In the Northeast and North Central U.S. the two most common mantids are non-native species: the Chinese mantid, and the European mantid. These were both introduced in the 1800s for pest control. Mantids are extreme generalists…
Q. [Laughter.] That’s a nice way to put it.
A. They are very effective visual hunters that will feed on any sort of insect they can catch. So yes, they will eat pests—they may eat aphids, or even grasshoppers, things that are eating plants, including beetle pests. But they will also eat insects that are not having a negative impact on the garden, those that are having a positive impact: pollinators, and other predatory species.
Q. So they are indiscriminate, and just hungry all the time.
A. They can be a great way to get kids to get excited about entomology. They are present in the garden, so I would keep a close eye out for them, and probably wouldn’t spend the money on releasing them. You’re likely to find them in the garden. Mantids have one generation a year, so this time of year [late spring-early summer] you’re going to be seeing the immature stage, the nymphs, and a little later in the summer the adults.
Q. Another group I was interested to read about in your new book: stink bugs. Everyone hates stink bugs, but is that bad reputation deserved across the board?
A. The stink bug family is a large family of insects, including both herbivorous species and predatory species. Some of the herbivorous species are significant crop pests. One of them is an invasive pest—the brown marmorated stink bug.
There are actually several species of predatory stink bugs found in the U.S. One of the most common in the Northeast, for example, is the spine soldier bug. It has kind of pointy shoulders, and a black spot on the end of its wing tips.
Another common one that’s kind of cool, for people who grow potatoes: the two-spotted stink bug [above]. It has a black body with bright orange or red markings lining it, and it’s a predator of Colorado potato beetles [below].
Q. Then send some of those over. [Laughter.]
Q. It’s a natural enemy. Speaking of insects that people think they understand and may be leaping to incorrect conclusions: People have very strong feelings about wasps, bees, and hornets because of the worry about stinging, but I was fascinated to read in your book about adult wasps collecting insect prey to feed to their young. Some of them are predatory and insectivorous, at least in part of their diet.
A. There is a whole group of wasps that are non-stinging, as I mentioned: the parasitoid wasps. In the wasps that can sting, there is a large number of solitary wasps that do not make a papery nest where there are many workers and many larvae. This is where individual females will collect prey for her own offspring. These wasps are not aggressive; they nest in the soil or they make mud type nests, like potter wasps and mud daubers. These are really fascinating to watch as they provision their nests with prey.
They feed on a large diversity of prey, for example sometimes they’re really specific, like the cutworm wasp that finds cutworms, paralyzes them by stinging them, makes a little soil burrow, then drag the cutworm down into the soil burrow and lay and egg on the cutworm. Her offspring will develop on cutworms.
Another neat one I always get calls about: the cicada killer. It’s a very large wasp, more than a coupe of total inches in length, and they actually do catch adult cicadas. You can see them catching them in the air, which is pretty exciting if you can find some cicadas you want to watch for these.
They do the same thing—they make a soil burrow and bury the cicadas. They are large so they look threatening, but you’re not going to see a large nest of these giant wasps. Unless you’re grabbing them and messing with them, they’re not going to sting you.
Q. So bee [above] versus wasp—it’s not so simple as one is good or the other is bad, as people are sometimes guided because of fears. It has taken me a lot of years as a gardener to get over visceral reactions to insects and not recoil, instead saying, “This is interesting,” and looking closely, then going in and looking it up in a field guide or online.
A. And I really think that knowing more about anything makes it less fearful. When I first started as an entomologist, I was pretty afraid of spiders, and did a few research projects about spiders. Now I am absolutely am fascinated by them.
Q. With some insects, and especially larvae, they’re at ground level, or underground. In the spring a gardener might turn the soil and uncover larvae and say, “Ugh, that’s something awful, it must be bad.” But that impression isn’t always true, either.
A. Absolutely. There are whole food webs operating in the mulch, and leaf litter, and underground. Many predatory insects can be found underground, at least during part of their life cycle. You’ll find ground beetle larvae and other types of beetle larvae foraging within the soil community, looking for prey and feeding on below-ground prey. A lot of spiders can be found in the mulch layer and in leaf litter—wolf spiders are especially common there, and very beneficial. They eat a tremendous amount of prey, including many pests.
Q. We talked about conservation biological control—not importation or augmentation, but making more habitat. You have some interesting suggestions in the book to get us started on that as gardeners, including your “Sweet Seven” annual plants we can grow, that always do a good job at building up the population of beneficials.
The Sweet Seven are annual plants that can be seeded or plugged into even small vegetable gardens. They’re things like dill [above, with swallowtail larva on it, in Margaret’s garden], coriander, buckwheat, sweet alyssum, fava beans, Phacelia, and borage are the Sweet Seven. These plants all share that they are prolific nectar and pollen producers. All natural enemies will feed to come extent on nectar and pollen—even spiders will. I think that as gardeners we recognize that bees need those resources, but the natural enemies also need those resources, in addition to their prey.
Q. The ones that you just mentioned, like buckwheat, are not native plants—which we can also plant to encourage beneficials in our landscapes. But the great thing about the Sweet Seven is that this is something anyone can do, even in a portion of your vegetable garden, and it’s not instant but as close to instant as anything with plants can be.
Frank Morton, a lettuce and greens and calendula breeder out in the Pacific Northwest, told me to when your arugula or chervil or various vegetables are “done,” leave a little of each crop in the ground, and let it go to flower, and see how many diverse insects show up. And he is absolutely right, which is what you’re saying with the Sweet Seven.
A. With coriander, for instance—and mine always bolts…
Q. [Laughter.] Don’t worry, it’s not just you.
A. …there is the tendency to think, “This is done,” and take it out, but it will be teeming with beneficial insects. Leave it there. These can be container plants, or mixed with other flowering plants—you can create some really lovely plantings on small scales, and incorporate native perennials in other beds surrounding your landscape.
Q. I have to say: I think my two longtime in-ground water gardens really helps in the bug-building cycle. So much going on in there, and insects I don’t see elsewhere–stoneflies (which I think are herbivores), huge things called fishflies, crane flies, dragonflies of course who rely on water to reproduce. So much extra good insect action if we have water in the garden.
A. Absolutely. In the book I did include a few predatory bugs and beetles that you could find in water features. A tremendous diversity of insects will forage around pond features, and in pond features. The dragonflies being the most conspicuous.
A. And the damselflies, yes.
Q. I want to ask you about one of my favorite online tools about insects, BugGuide.net. You credit in the front of the book that contributors to BugGuide shared photos with you—and by the way, the book has great pictures in it.
A. Yes, the book has over 200 photos contributed by used of BugGuide, which is an amazing online resource for people who want to learn more about insects of any kind. It’s a website maintained by Iowa State University Department of Entomology. If you take a photo of an insect—you don’t have to be an expert—you can submit the photo and experts who manage that website will classify that photo for you. You will receive updates that it has been moved to a particular order, family or even species of insect.
It’s a great way to share insect photography, and to find out about the insects in your garden.
Q. It’s a user-generated community of knowledge. I’ve posted things on it and when we do, it’s not only to get ID but also to add to the knowledge base, to help scientists to know, “Oh, look, there’s a population of this insect in adult stage in this area of the country on X date…” and maybe inferences can be drawn from all these observations.
A. It’s a tremendous data bank for scientists as well. I use it to determine commonness of species—based on the number of photographs an insect received from across the country. Or an index of how interested people were in knowing more about a particular predator. If there were a lot of photos, it indicated to me that people were probably interested in knowing more about it. I used that as one way to pare down what I was going to include for each group in the book.
enter to win a copy of ‘good garden bugs’
I’VE BOUGHT an extra copy of Mary Gardiner’s new book “Good Garden Bugs” to share with a lucky reader. All you have to do to enter is comment in the box at the very bottom of the page, past the last reader comment, answering this question:
What’s your favorite, and your least favorite, bug (whether a true insect or a spider)?
Me? I suppose I find most every insect fascinating–especially moths, as you may recall–and consistently only really loathe a couple: red lily beetles, and Japanese beetles. Well, and maybe ticks (but they’re surprisingly interesting, too, as I wrote about recently).
No answer, or feeling shy? Say, “Count me in” or some such thing, but an answer’s even better. I’ll draw a random winner (U.S. or Canada only) after entries close after midnight Sunday, July 5, and will notify that person by email. Good luck to all.
prefer the podcast?
MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its sixth year in March 2015. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the June 29, 2015 show right here, and also use the buttons below to subscribe to future shows, free.
(Photo credits: Carolina mantid by D. Shetlar; two-spotted stink bug by ThomasBentley.com; potato beetle, ichneumon wasp, bee, larvae in dill by A Way to Garden. Disclosure: Purchases from Amazon affiliate links yield a small commission.)