Good Bugs. Bad Bugs.

Good Bugs. Bad bugs.

By Lois Hole

A lot of gardeners have a fit if they catch a glimpse of some creepy-crawly slithering over one of their plants. Not me. Not all bugs are vicious beasts intent on devastating your garden; the vast majority of insects are either beneficial or have no effect on humans. Of the 15,000 insect species that interact directly with humans, only 3,000 have been identified as pests, a definite minority. Knowing the difference between good and bad bugs can save you time, stress, and money.

Insects play an important role in Earth’s ecosystem. Here are just a few of the vital products and services insects provide: they pollinate many of our food crops; they break down dead, decaying matter; they help to keep soil healthy by aerating, decomposing, or adding nutrients; they serve as food for larger animals; and they provide silk, honey, shellac, and dyes. Insects are also important in research, acting as experimental objects in many fields, including genetics, physiology, ecology, and behavior. Clearly, we would be in real trouble without insects.

Good Bugs

The ladybug, for example, could be called the gardener’s best friend. Almost everyone recognizes these beneficial insects; the adults are hemispherical, red-orange to yellow, with varying black spots or bands, while the larvae are elongate and dark-coloured with black or orange lateral spots. Both ladybug larvae and adults prey on soft-bodied insects like aphids; in fact, ladybugs are incredibly voracious, eating many times their body weight in aphids in a single day. If food is limited, ladybug adults will fly off in search of greener pastures, though some ladybug strains, available from commerical sources, have had this trait bred out or addressed during rearing so that the ladybugs stay in one area.

Lacewings are great friends to the gardener, too. They are pale green, slender-bodied insects with lacy wings extending over the abdomen and beyond. Their larvae—elongate, hairy, and dark—are what will take care of your aphid problem. Like ladybugs, lacewing larvae love aphids and will gobble them up with gusto.

Parasitic insects come in a wide variety of forms; there are many species of wasps and flies that lay their eggs in or on their preferred host. The eggs hatch and the host insect is consumed from the inside out, a gruesome but effective way of dispatching the prey. Parasitic wasps and flies attack a wide range of insects; soft-bodied pests like aphids, caterpillars, and beetles are legitimate food, though a particular species of parasitic insect generally attacks only one species of prey. A wasp from Europe, Lathrolestes luteolator, is doing a superb job of attacking the birch leaf miner.

Flowerflies in the adult stage bear a striking resemblance to bees. Like bees, flowerflies are important pollinators of flowering plants; they feed exclusively on nectar and pollen. Their larvae are elongate, legless maggots that feed on aphids and their relatives.

There are a number of other creatures that feed on garden pests. Yellowjackets and hornets may be annoying, but they won’t attack you unless provoked; they would much rather spend their time searching for prey, namely medium to large insects. Spiders of all kinds are exclusively predators. Orb-weaving spiders will capture moths, flies, and beetles in their webs, while other spiders will simply lie in wait inside flowers and attack any unwary insects that happen along. Finally, predatory mites feed on spider-mites, fungus gnats, and thrips. They are tiny creatures, but efficient; some are active on the foliage, while others work in the soil.

Although we have seen that most insects are beneficial or harmless, there are some that pose a serious threat to crops. Fortunately, there are ways to deal with these pests.

Bad Bugs

The Colorado Potato Beetle is one of the most notorious pests in the garden. The adults are 6-15 mm long, oval in shape, with 10 longitudinal black stripes on a yellow background. The eggs are elongated and orange, and are laid on the underside of leaves. Eventually, they will hatch into crescent-shaped orange larvae with lateral black dots. Both adults and larvae chew on leaves, and they usually feed in groups; plants can be stripped of their leaves in no time. As the name implies, these insects prefer potatoes but will also attack tomato, eggplant, pepper, petunia, and thistle.

To manage this pest, check your plants every spring, searching for adults and eggs. Handpick all that you find, and you should have few problems for the rest of the season. Adults can survive over the winter by burrowing into the earth, so rotating crops can help alleviate the problem by leaving the emerging beetles without a food source. If you need to spray, use House & Garden Protector.

Aphids are tiny—only 1-3 mm long—but they can cause large amounts of trouble. They are soft-bodied insects that range from yellowish-green to black in colour. They reproduce at an incredible rate; most aphids don’t even require a mate to give birth during the summer months. When food quality declines or overcrowding occurs, a winged generation is produced. This more mobile crowd of aphids migrates to another area of the garden or greenhouse to begin the cycle anew. It’s easy to see how aphids can quickly infest entire crops. They spread viruses, too.

Aphids attack nearly all vegetables, sucking the juices out of the plants. You’ll find them feeding on buds, stems, or, most commonly, on the undersides of leaves. If your plants are wilting, if they have malformed buds, stunting, yellowish leaves, and a sticky, shiny substance on the leaves (the aphid excreta), then you’ve probably got an aphid infestation to deal with.

One method of managing aphids is to spray your plants with cold water, preferably in the morning. The jet will blast many aphids off the plants and drown a good deal of them. If that fails, you may need to spray with Trounce or House & Garden Protector.

Cabbage and onion maggots will also cause you a good deal of grief if they get into your vegetable patch. The adult flies resemble small houseflies, about 5 mm long and gray. They emerge in late May to early June and will start laying eggs near the base of the host plant after a rain, when the soil is moist. (Egg laying coincides with the flowering of Saskatoon bushes.) When the eggs hatch, the maggots that emerge will burrow into the roots of the host, where they feed. Cabbage maggots primarily attack plants in the mustard family—cabbage, cauliflower, broccoli, radish, and turnip. Onion maggots, naturally, like onion, but they will also infest garlic, leek, and chives. Damage symptoms include wilting and yellowing of the outer leaves. Cabbage and onion maggots like moist soil, and they’re less of a problem in drier years.

One of the best control methods is to lay down newspapers or commercial root maggot collars around the base of the plants. The adult flies will lay their eggs on the surface, where they will dry out and die. Keeping the garden free of weeds will also help. 

If your vegetable leaves have dozens of holes in a “shotgun” pattern, you may have flea beetles. Flea beetles attack potato, cabbage, turnip, cucumber, lettuce, cauliflower, radish, bean, tomato, or pepper. Adult beetles are quite small, about 1-2 mm long. They are dull black to metallic blue, or orange and black.

The best way to fight flea beetles is to control weeds that act as spring hosts—stinkweed, shepherd’s purse, and wild mustard. If chemical controls are used, spraying should be done when the plants are emerging from their hills and have reached a few centimetres in height, usually around the end of May or the beginning of June. If you spray, use House & Garden Protector. Also, check the label (on any pesticide) to see how many days you should wait before it’s safe to eat any fruit or vegetables you harvest.

Tarnished plant bugs are flat, oval-shaped insects about 4-6 mm long; their larvae resemble aphids. They attack alfalfa, canola, and most vegetables, fruits, and flowers. The adults emerge in the spring, feeding on weeds at first and then migrating to crops and gardens in mid-May to mid-June. In addition to eating your plants, they will also lay eggs on leaves and stems. Tarnished plant bugs may cause plant leaves to become deformed, stems to be scarred and discoloured, and buds and fruit to be dwarfed or pitted.

Removal of broadleaf weeds will help to reduce the build-up of this pest. Also, be aware of any alfalfa or canola crops grown near your garden; a large influx of these pests can occur after such crops are sprayed or harvested. House & Garden Protector will kill tarnished plant bugs.

The best way to control insect pests is to take good care of your garden. That means regular, consistent watering, careful weeding, rich soil, proper fertilizing, and a good location with plenty of sun and good air circulation. Insects are less likely to attack healthy, hardy plants.

Insects might not be pretty, but they are important. So the next time you’re tempted to squash one, remember that you just might be stepping on a friend.