The Fly That Controls Japanese Beetles

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The Japanese beetle is universally detested by gardeners … but a small fly is now helping to control its population. Source: Judy Gallagher, Wikimedia Commons

Ever since the Japanese beetle (Popillia japonica) first showed up in New Jersey in 1912, apparently brought over from Japan in a shipment of bulbs, farmers and gardeners have been desperately seeking an easy way to control it. And it’s now made it to Europe as well, with outbreaks in Italy, Russia and, since 2017, Switzerland.

When you have Japanese beetles, you know it. The adults seem to make little effort to hide. The metallic green beetles with coppery wing cases gather by the thousands and munch their way through foliage and flowers alike, leaving devastation in their wake. The worst hit plants have no untouched leaves at all, just browning ones with intact veins. And this pest attacks a wide range of plants (read Japanese Beetle Host Plants). To make matters worse, Japanese beetles attack in mid-summer, just when your garden should be at its finest!

And it’s not just leaves and flowers! Underground, their larvae chomp away on grass roots: yes, they’re among the various scarabs whose larvae we call white grubs, so hated by lawn owners everywhere.

In other words, Japanese beetles piss pretty much everybody off!

An Attempt That Fails… Then Succeeds!

Back in Japan, the Japanese beetle has several predators to contend with and, as a result, the population generally remains low and damage is minor.

American researchers tried to capitalize on this by introducing, starting in 1927, a serious of insects that feed on Japanese beetles in its native habitat. However, the first trials seemed unsuccessful. But it turns out at least one insect, a tachinid fly called the winsome fly (Istocheta aldrichi), has adapted better than was thought at the time. (Another Japanese beetle predator, a parasitoid wasp known as Tiphia vernalis, is doing fairly well too, although its range today is less extensive.)

The winsome fly hadn’t done well in New Jersey tests, because in that climate, the life cycles of the two insects barely overlapped. The adult fly—the egg-laying phase—tended to emerge too early and was near the end of its cycle by the time the Japanese beetles emerged in their turn in July. Thus, few JBs were parasitized and it was thought the experiment had failed. However, several decades later, the winsome fly was found again. It had made it further north on its own, to New England, where the cooler springs delayed its emergence enough so the two life cycles overlapped much more effectively. In some areas, in some years, up to 80% of all Japanese beetles that emerge have been found parasitized.

Winsome flies are still on the move! Even as Japanese beetles continue to expand their range in North America (they’re now present in most US states and Canadian provinces), so do winsome flies. They’re now found in most of the Northeastern US states and recently reached Canada where they’re thriving and spreading in Ontario and Quebec.

The Life Cycle of a Beetle Predator

The winsome fly is a parasitoid: it doesn’t just live on its host, it kills it!

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Winsome fly (Istocheta aldrichi). Source: National Collection of Insects, Arachnids and Nematodes

It’s a small grayish fly about 5 mm long, looking much like any other small true fly. It emerges just a short time before the Japanese beetles do and builds up its energy by feeding on flower nectar. When the Japanese beetles appear, the female fly starts laying white eggs on her host’s thorax, just behind its head. They are easily visible, at least if you have your glasses on.

The fly will lay a hundred eggs over the second two weeks of its 4-week emergent cycle. It tends to mostly parasitize female beetles, because they spend much of their time pinned under male beetles trying to mate with them and thus can’t readily escape the fly. Japanese beetles not mating react rapidly when winsome flies are around, quickly dropping to the ground.

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Eggs on the thorax of a few Japanese beetles. Source: blog.uvm.edu

The eggs hatch in about 24 hours. Even if the beetle carries several eggs, only one larva will actually penetrate the body of its victim where it will begin to digest it from the inside. First to go are its flight muscles, leaving the beetle unable to fly. The beetle then goes into protective mode, falls to the ground and buries itself.

The infested beetle dies only 5 to 6 days later, but the fly larva remains in the dead body of its host all winter as a pupa, then the cycle begins again the following summer. There is only one generation per year.

Note that this predation occurs as adult beetles are emerging, before they lay eggs. Since the female JB would have normally laid 40 to 60 eggs, that many fewer beetles will be born the following year!

Winsome flies will also predate, to a lesser extent, other white grub-producing scarabs, like European chafers.

Encouraging Winsome Flies

The winsome fly is not commercially available. You have to wait for it to show up in your area on its own.

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Umbellifers with their small, clustered flowers, are favorites of winsome flies. The blooms above are those of coriander (Coriandrum sativum). Source: H. Zell, Wikimedia Commons

Once they have reached your neighborhood, anything you do to attract a horde of winsome flies to your garden will help. For example, plant many small, shallow-flowered plants, such as umbellifers (coriander, dill, lovage, etc.), crucifers (sweet alyssum, mustard, etc.) and Asteraceae (chamomile, daisies, yarrows, etc.) to attract and feed the flies.

Also, avoid spraying insecticides. They usually affect the fly (our friend) more than the unwanted beetle… plus once you start seeing eggs on Japanese beetles, you need a new strategy: killing them all is no longer that useful.

Less squeamish gardeners—or those that most hate Japanese beetles!—can hand trap them and sort them, letting parasitized beetles go free (remember, they’ll be underground and out of sight in just a few days) and dropping unparasitized ones into a pot of soapy water. I don’t know how you’ll explain this to your neighbors, though!

The Result?

Winsome flies will never completely eradicate Japanese beetles. No wise parasite ever totally eliminates its host: that would be suicidal!

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With winsome flies in the area, you should no longer see such complete defoliation of your plants. Source: www.ontariohopgrowersassociation.ca

Where Japanese beetles occur, you’re unlikely ever to get rid of them entirely, so should choose plants accordingly (see Plants That Japanese Beetles Tend to Avoid). However, by eliminating the most beetle-susceptible plants from your garden, replacing them with ones they dislike and encouraging winsome flies and other predators by supplying nectar-rich flowers, you’ll find the number of beetles can drop significantly in just a few years. Many gardeners in areas where the winsome fly is well established say they can now garden much like they used to before JBs appeared, since the few remaining ones do little damage.

Breaking News!

Shortly after this article was published (like, about 10 minutes later!), I received word that the Montreal Botanical Garden is undertaking a study to determine the extent of the distribution of this parasitoid fly in Canada and asks Canadian gardeners to participate. If you see a Japanese beetle bearing the telltale white egg(s) of the winsome fly, please take a photo and send the information, along with pertinent details (there’s a short form to fill out) to the Entomological Information Service at Space for Life.

Thanks to Sandrine for this information!


The expansion of the winsome fly is therefore very good news for many gardeners and farmers! If combining a choice of JB-resistant plants with a small parasitoid fly can make gardening easy again, who’s likely to complain?20180707C blog.uvm.edu

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In Praise of Tall Trees

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This is what the suburbs used to look like: modern developments however are sadly lacking in big trees. Photo: Fgrammen, Wikimedia Commons

An important element of residential landscaping seems to be going the way of the dodo in modern cities. Tall trees — the big, majestic ones that gave the landscape its character — are increasingly being left out in favor of smaller trees or even shrubs grafted on short trunks.

This is a fairly recent trend. If you look suburban developments over 60 years old, tall tree species dominate. Big maples and huge majestic oaks are everywhere. They helped create an atmosphere of tranquility and well-being. Take a walk in a neighborhood 40 years old or less, though, and you mostly see green lawns and shrubs, maybe a flower bed or two, and a few smaller trees you couldn’t even fit a lawn chair under, but not many larger ones. True enough, a somewhat sparse landscape can be still attractive, but it tends be so in a cold and impersonal way. Such neighborhoods aren’t really inviting. It’s as if the residents planned all along to leave their dreary home landscape on weekends for a break at the cottage … surrounded by tall trees, of course!

Just Don’t Think About It, Plant Them!

Why do larger trees deserve a place in suburban and urban lots?

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Taller trees create a homey, friendly, inviting atmosphere. Photo: Bridan Stansberry, Wikimedia Commons

First, for the shade they offer. Gardeners may complain you can’t grow anything under big trees (actually, you most certainly can: I’ve written an entire book about shade gardening, so I know it’s far from impossible!), but the fact is we’re attracted by shade. During the dog days of summer, a neighborhood well decorated with broad, shade-producing trees is livable; one denuded of any tall vegetation simply is not.

Also, human beings, by their very nature, seem to need trees in their surroundings. Is this a reminder of the long distant past when our ancestors took refuge in trees when they were attacked by predators? No one knows. Still, the feeling of peace and security that emerges from a big tree seems very real. In fact, it can be seen in different cultures all over the world: when people are given a choice of where they would like to live, they inevitably prefer not a forest, but a landscape dotted with mature, tall trees.

Of course, maybe you do feel you have trees on your property. But can you really call a small weeping tree barely 10 feet (3 m) high a tree? Or a flowering crabapple or a Japanese lilac or one of the many other “small trees” so heavily planted these days? They may be trees by definition, but you can’t walk under them without bumping your head, you can’t fit a lawn chair underneath them without your legs sticking out in the hot sun and they don’t create the atmosphere of permanence and security that large trees can provide.

How to Use Trees Wisely

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Bravo: this modern homeowner has included one tree that will reach a reasonable size. But look at the photo: wouldn’t it be more attractive with at least one tall tree reaching up from the back yard as well?

Ideally, to recreate the sense of peace and permanence you want, you’d need at least one large tree per yard. Preferably two, in fact, on in the front and one out back. Obviously, the larger the lot, the more trees it needs.

In addition to the atmosphere they create, big trees offer other advantages:

  • Reduced cooling costs in the summer;
  • Reduced heating costs in winter;
  • Minimal maintenance;
  • Increased land value;
  • An environment healthier for human physical and mental well-being;
  • An inviting landscape for our feathered friends;
  • And much more.

Trees have certain disadvantages, of course, but these are generally easy to overcome.

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Planting a tree takes a bit of effort. Photo: Maryland GovPics, Flickr

Planting them, for example, is fairly arduous … but at least you only have to do it once!

The shade they produce will reduce the choice of plants that will grow underneath, but there is still a good choice of shade plants. Where it’s too shady for a dense lawn, for example, there are dozens of equally dense, maintenance-free groundcovers.

Some trees do produce seeds or fruits that can be briefly annoying when they fall, but there are many cultivars that are either sterile or male (male trees produce no seeds).

Finally, there will be leaves to rake up each fall — yes, even so-called evergreens tend to lose leaves at that season —, but fortunately that’s only a once-a-year thing … much less work than maintaining a lawn, which usually requires weekly mowing.

Plant Tall Trees Where They Can Reach Their Full Size

When planning to buy a tree, ask about its maximum height and spread and use that info to find a suitable location. For example, don’t plant it where it can interfere with overhanging wires, too close to the house, or directly in front of a window. Nor should it reach over into a neighbor’s lot, otherwise there is a serious possibility of conflict.

Lots of choice!

What follows are some suggestions of tall trees (over 30 feet/9 m) that can decorate your property. All are low- to no-maintenance trees that will enhance your property’s value.

Note that the trees shown here were chosen for a cold climate region. In areas with more temperate or even warm climate, you’ll have an even greater choice. Measurements are averages reached under normal growing conditions.

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Red maple in its fall glory. Photo: Famartin

Red maple (A. rubrum): Long neglected by arborists, this North American native is becoming more popular, especially in colder climates. Its bark, smooth and pale gray in its youth, becomes rough over time. Its three-lobed leaves turn bright red in autumn. Prefers moist growing conditions. Height: 60 feet (18 m). Spread: 50 feet (15 m). Hardiness zone: 3b. There are also smaller, more symmetrical selections, such as ‘Morgan’ (50 x 50 feet/15 x 15 m) and ‘Red Sunset’ (30 feet x 20 feet/9 x 6 m). ‘Autumn Flame’ (35 x 20 feet/11 x 9 m) is the best choice for colder climates (zone 3).

Freeman Maple (A. x freemanii): This hybrid maple results from a cross between red maple and silver maple (A. saccharinum), but is closer to red maple in overall habit. It’s perhaps even superior to red maple as a city tree and is even a bit hardier: zone 3. There are several cultivars, including Autumn Blaze (‘Jeffersred’), 50 x 30 feet/15 x 9 m), which turns fiery red in the fall.

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The orange-red fall color of the sugar maple. James St. John, Flickr

Sugar maple (Acer saccharum): It used to be that arborists shunned this North American native, considering it unsuited to urban areas, and recommending Norway maple (A. platanoides) instead. Nowadays, attitudes have changed and that there are few situations where a sugar maple wouldn’t be considered a better choice than its Norwegian relative. Planted in isolation, it takes on a beautiful speading, rounded shape quite unlike its fairly scrawny appearance in forested areas. With its excellent orange-red fall color, it’s also much more colorful than Norway maple and less subject to winter damage. Plus its smaller, rapidly decomposing leaves have less tendency to choke out grass. Finally, it isn’t subject to tar spot disease, this disease which turns the leaves of Norway maple into an unsightly mess. Both, however, do have dense and shallow roots: there’s no denying that maintaining a perfect lawn under either maple is a challenge, though. Height: 60 ft (18 m). Spread: 40 feet (12 m). Hardiness zone: Zone 4. There are several horticultural selections, including ‘Green Mountain’ and ‘Legacy’, which offer a more regular habit on a somewhat smaller tree than seed-grown sugar maples.

Common Hackberry (Celtis occidentalis): This North American tree looks a bit like an elm but with a more rounded crown. Corklike bark. Yellow color in autumn. Height: 65 feet (20 m). Spread: 50 feet (15 m). Hardiness zone: 4.

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Ginkgo starting to take on its fall color. Photo: Crusier, Wikimedia Commons

Ginkgo (Ginkgo biloba): Very slow growing, but totally resistant to insects and diseases. Attractive yellow foliage in the fall. Always ask for a male specimen: the females drop messy, stinky fruits. Height: 45 feet (14 m). Spread: up to 40 feet (12 m), but much narrower than wide for the first 60 years or so. Hardiness zone: 4.

Honey Locust (Gleditsia triacanthos inermis): Tree with an open, often irregular crown that lets sun through. Rough bark. The compound leaves are composed of leaflets so small that they decompose quickly: you don’t even have to rake them up in the fall! The extremities of the branches often freeze during the winter in colder climates, but that doesn’t really affect its appearance. Look for the cultivars ‘Moraine’ and ‘Skyline’, as several honey locusts, like ‘Sunburst’, are too small to make good shade trees. Height: 65 feet (20 m). Spread: 55 feet/17 m. Hardiness zone: 4b. ‘Northern Acclaim’ is an extra-hardy variety: zone 3.

Amur Cork Tree (Phellodendron amurense): Little known, but very attractive and virtually without cultural problems. The bark on mature specimens is very corklike. Height: 40 feet (12 m). Spread: 40 feet (12 m). Hardiness zone: 3.

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Siberian pear is an easy-to-grow, heavily blooming tree well worth discovering. Photo: Sten Porse,  Wikimedia Commons

Siberian Pear (Pyrus ussuriensis): A large tree that dwarfs its smaller fruit tree cousins: apples, plums, cherries, etc. It’s also essentially immune to most of the diseases and insects afflicting fruit trees. It blooms abundantly in spring, covering itself with white blossoms, but its tiny fruits are of no interest to humans, although they do attract birds and small mammals. It will only bear fruit if there are two different clones in the area, since cross-pollination is obligatory for this species. Height: 40 feet (12 m). Spread: 33 feet (10 m). Hardiness zone: 3.

Oaks (Quercus spp.): A large group of trees, most tall and spreading, generally with toothed leaves. They’re considered among the most majestic of trees, but their growth is fairly slow, at least after the first 10 years or so. Height: 65 feet (20 m). Spread: 50 ft (15 m). Hardiness zone: generally, zone 4. Red oaks (Q. rubra) and scarlet oaks (Q. coccinea) are particularly interesting for their massive shape and fall color. Where space is limited, consider columnar English oak (Q. robur ‘Fastigiata’) which reaches the same height as the other oaks but rarely exceeds 13 feet (4 m) in diameter. The best oak for cold climates is bur oak (Q. macrocarpa), hardier than the others: zone 3. Shingle oak (Quercus imbricaria) is unusual among hardy oaks in that it has narrow untoothed leaves.

Think-Twice Trees

The following trees may be useful in some cases … but have problems that can seriously reduce their usefulness under certain circumstances. It’s up to you to decide whether they are worth growing under your conditions!

Horse Chestnuts, Hickories, Walnuts (Aesculus spp,. Carya spp., Juglans spp.): They make beautiful trees, but their large fruits can be an annoyance, especially near roads. In addition, walnut trees are allelopathic (toxic to plants that grow at their base).

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River birch

Birch (Betula spp.): Most make very nice trees, with attractive bark, but they’re often short-lived (especially silver birch [Betula pendula] and its varieties) and rarely make it to their full size. In addition, they are susceptible to a wide range of diseases and insects and that can mean a lot of spraying … under some circumstances. Ask a local arborist their opinion, as the problems tend to vary greatly, from minor to major, depending on local conditions. One exception is river birch (B. nigra), especially the cultivar Heritage (‘Cully’), with bark that exfoliates gracefully: it’s long-lived and disease- and insect-free under most conditions. Height: 50 feet (15 m). Spread: 35 feet (10 m). Hardiness zone: 3.

Catalpa (Catalpa spp.): Although catalpas survive in cold regions and thus some nurserymen rate them as zone 4 trees, in fact, they tend to suffer severe winter damage in zones 4 and 5, at least periodically, and, as a result, grow very irregularly. With their abundant white to lavender blooms, they make an excellent choice in areas 6 and up, though. Height: 50 feet (15 m). Spread: 30 feet (9 m).

Linden (Tilia spp.): Tree with a strong trunk and heart-shaped leaves, plus highly scented flowers. The little-leaved linden (T. cordata) is very popular and offers many interesting cultivars, however … this genus is not a good choice in regions infested with Japanese beetles, as they literally defoliate the tree every summer. Height: 100 feet (30 m). Spread: 80 feet (25 m). Hardiness zone: 3.

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Ulmus x ‘Morton’ Accolade is a hybrid elm the looks like an American elm, but is resistant to Dutch elm disease. Photo: Bruce Marlin

Elm (Ulmus spp.): American elm (U. americana) almost inevitably falls victim to Dutch elm disease, which is difficult and expensive to fight. There are, however, several elms, including hybrid varieties, which share the American elm’s majestic upright spreading habit while showing good resistance to the disease. Before buying an elm, always ask if it’s resistant to Dutch elm disease. The Siberian elm (U. pumila) is resistant to Dutch elm disease, but is a weak-wooded tree with a poor growth habit and susceptibility to other diseases. Plus it self-seeds excessively and is considered an invasive species in many areas.

Trees to Avoid at All Costs

Ash (Fraxinus spp.): The arrival of the emerald ash borer (Agrilus planipennis), a deadly tree-piercing insect, in North America—and even now in Europe—has killed pretty much any interest in this formerly popular street tree. You might want to maintain the ones you have, but it’s probably wise to avoid planting new specimens.

Poplars, Willows, Silver Maple (Populus spp., Salix spp., Acer saccarhinum): The roots of these fast-growing trees are extremely invasive and often cause damage to domestic and municipal water and sewage pipes. They often also sucker extensively or self-sow and so become very invasive. It’s illegal to plant these trees in most municipalities.


There you go: a list of big and beautiful trees you might want to consider growing. And don’t delay, as it will take a few years before you can savor their full effect on your property!20170528B Fgrammen, WC