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Science & NatureEnvironmentAlien insects: The gardener’s nemesis

Alien insects: The gardener’s nemesis

by Theresa Peluso

How does your garden grow? Are alien insects a challenge?

Most of my previous articles have described changes to Lanark County’s natural environment in general.  This time I’d like to address a topic of special interest to me – my garden in Blakeney.  A closely related topic is garden enemies, which in my case mostly consist of invasive insects.

I see my garden as a piece of nature that I have cultivated to reflect my desire for beauty and life.  Creating a garden is a challenge on many levels.  There’s the esthetic element, too complicated to describe here, the physiological element (growing plants in the right location according to their needs for space, light, water, appropriate temperature, and soil type), and finally there’s the spiritual aspect, in which my garden is part of the life that surrounds and nurtures me.

In my garden I have made a point of growing several native species of plants (although I must confess that I have many non-native plants too), as well as perennials, bushes and trees that attract birds and bees. I also have a vegetable garden close to the kitchen, which provides a delicious bounty of beans, Swiss chard, zucchini, cucumbers, tomatoes, peppers, lettuce and garlic. My plants are mostly undemanding, and my husband and I use environmentally friendly products to fertilize them, mulch them, and protect them from insect invaders.

I get the impression that insects weren’t much of a problem 200 years ago.  Sure, there were ants, grasshoppers, weevils, aphids, potato beetles and cutworms, but nothing like what we have now. Read on for the list of Canada’s Least Wanted alien invaders.

The Asian gypsy moth was introduced to North America in the 1860s by a French scientist living in Massachusetts.  He wanted to make a silkworm hybrid that could resist diseases by interbreeding silk worm moths and the gypsy moth, and in the process unleashed one of the most destructive pests of hardwood trees. Next in the line-up, the European earwig, which reached British Columbia via the United States in 1919. They enjoy dining on your lettuce, tender seedlings and flowers.  They do have some redeeming qualities, however, since they also feed on aphids, mites, fleas and insect eggs.

Gypsy moth

One culprit that I dislike with a passion is the viburnum leaf beetle, first found in North America in 1947, and in the Ottawa-Hull area in 1978.  Do I enjoy seeing my blue-muffin viburnum bushes attacked by hordes of these evil creatures, both in their slimy, little brown larval stage and their mousy-brown adult stage?  Do I like seeing the viburnum leaves reduced, year after year, to crispy, wispy, skeletal shapes despite all my attempts to spray these villainous insects with organic soaps, and that having failed, handpicking and squeezing the little so-and-sos by the hundreds, only to have hundreds more appear the following day?  It has gotten to the point where I have finally dug up the bushes, and replaced them with snowmound spireas.

If you like Asian lilies (yes, I know, they’re not a native plant), then you will be well-acquainted with the lily leaf beetle, which made its first Canadian appearance in Montreal in 1945. If not monitored and killed on sight, they can destroy your lilies, leaving you with vestiges of green leaves and stems.


Emerald ash borer

If you have a wooded property, be afraid, very afraid of invasive insects like the emerald ash borer, introduced to North America from Asia in the 1990s.  Since that time, it has killed at least 50 to 100 million ash trees, and it continues to wreak havoc as it spreads east.  Just as the Dutch elm disease spread by the elm bark beetle has killed most of our elm trees from the 1950s on, the same could happen to most of the 7.5 billion ash trees in North America. The warmer year-round temperatures resulting from climate change help this insect to survive our winters.

There’s also the Asian long-horned beetle, which arrived in the United States in 1996, and has since spread to Canada. Unlike the emerald ash borer, the long-horned beetle attacks a variety of trees, including maple, elm, willow and birch trees. The brown spruce longhorn beetle, on the other hand, native to Europe, and introduced to Canada in the 1990s, attacks and kills spruce trees.  It is a huge threat to the forests of North America.

Limited space prevents me from elaborating on yet more invasive aliens, such as the Japanese beetle, introduced to Canada via Yarmouth, Nova Scotia in 1939; the spotted wing drosophila (a kind of vinegar fly) from Asia, first detected in North America in 2008, and now found in several Canadian provinces, including Ontario; and the brown marmorated stink bug from Japan (or Korea, Taiwan, or China), which first appeared on this continent in 2001, and is expected to cross our border in the near future.

What can we do about it?  First, eliminate or minimize the spread of these invasive species. They hitchhike their way to new locales on luggage, merchandise (especially plant products), and vehicles, so make sure you’re not the one giving them a free ride. If you see an unusual insect causing damage to your garden, find out what it is, and what environmentally friendly measures you can take to eliminate it.  Any evidence of insects that destroy trees, such as the emerald ash borer, should be reported to the Ontario Ministry of Natural Resources, so they can take the necessary steps to limit the damage to our forests. The Canadian Food Inspection Agency keeps track of newly introduced pests, and checks for selected invasive alien species that may arrive in Canada.

Try to work with nature to control these harmful pests.  Encourage frogs, toads, birds, spiders, ladybugs, lacewings, pirate bugs, and praying mantis in your garden by providing habitats that invite them to take up residence. Some insect-eating animals such as bats and several kinds of birds are not as plentiful as they used to be because of new diseases (such as white-nose syndrome, which has resulted in the deaths of at least 5.7 million to 6.7 million North American bats), and climate change and habitat destruction (which has depleted the numbers of many birds, such as chimney swifts, nighthawks, purple martins, and barn swallows).  Despite these worrisome trends, these birds can still be found in our county, and of course, other birds, such as orioles, woodpeckers, wrens, nuthatches, goldfinches, cardinals, bluejays, and chickadees, also eat insects.

In the spring, before your trees and bushes come into leaf, spray them with dormant oil to kill any overwintering parasites.  If you see a soft-bodied insect, spray it with insecticidal soap, or soap in combination with pyrethrin (derived from the chrysanthemum plant). Nematodes, application of a bacterium called bacillus thuringiensis, and diatomaceous earth are also environmentally friendly ways to reduce or eliminate pests. To prevent access to your plants by these nasty bugs, you can also use physical barriers, such as sticky tree bands, collars, row covers, and even panty hose!  Avoid using chemical or petroleum-based fertilizers, which interfere with the integrity of the soil structure.  Instead, use compost, manure, peat, seaweed, and bone meal to promote healthy plants.  And why waste time and energy growing high-need plants when you can find plants that are better adapted to your garden’s environment?  (Lesson learned:  I should have done my research on viburnum bushes before planting them.)

So, unlike 200 years ago, gardeners and tree growers have a slew of new insect pests to deal with.  Although in some cases, at a national or provincial level, chemical warfare and plant removal may be necessary to stop their spread, at the local level we need to work with nature to reduce the harm these alien invaders can cause to our beloved trees and gardens.





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