Good Bugs — Bad Bugs
There’s an old garden saying: Plant it and they will come. They come crawling, flying, jumping, burrowing, and walking to the buffet we have created in our landscape gardens. Their numbers are staggering; it’s estimated that at any given time there are 10 quintillion (that’s a lot of zeros – 10,000,000,000,000,000,000) insects living on earth. Sometimes I believe that most of them have journeyed down the pathway to my garden.
Fortunately, the good news is that out of the 800,000 – 1,000,000 species of insects that have been identified/described so far, not more than 1,000 (about 1/10 of 1%) can be regarded as serious pests, and less than 10,000 (about 1%) are even occasional or sporadic pests. This 1% gives the majority of the insects in the garden a bad name. The remaining 99% are either harmless or beneficial. The harmless insects add a little color and diversity to the garden without threatening our plants. The beneficial insects pollinate our flowers or eat pests. However, at some point, bad bugs will show up in the garden, usually accompanied by lots and lots of hungry friends. Some insects bore into roots, seeds, or stems. Many suck large quantities of plant sap. Others destroy plants and crops by chewing on the succulent foliage, stems, or fruits. Adding to the challenge, some insects, such as the cucumber beetle, transmit diseases that can be fatal to plants.
As frustrating as an insect infestation can be to a gardener, insects perform many activities beneficial to our gardens and to the environment. Insects are an important source of food for many animals, including birds, fish, and frogs. Insects are vital as pollinators, and pollination is essential for most food crops and flowering plants. Many insects are important predators of pests in our backyard gardens. Part of the reason many other insects don’t become pests is because there are good insects in the environment preventing an infestation. Also, insects play a critical role in recycling and eliminating waste materials, which helps keep soils healthy.
Good bug or Bad Bug?
In the world of nature, an insect is neither good nor bad. Each insect has an essential role in maintaining a healthy and balanced ecosystem. As gardeners, however, we don’t always see the complete picture. We typically define an insect as good or bad according to whether or not the insect assists us in meeting our human goals.
Is it a good bug or a bad bug? Well, it all depends. I am delighted when I see an assassin bug stalking a tomato hornworm caterpillar on one of my prized heirloom tomato plants. On the other hand, a butterfly enthusiast observing an assassin bug attacking a caterpillar in a butterfly garden may have a different perspective. It’s also a question of the right bug in the right place. If I mow over a nest of yellow jacket wasps buried in the lawn in mid August and get attacked by a zillion unhappy stinging warriors, I tend to forget that wasps are an ally. Their appetite for reducing the number of flies doesn’t seem all that important.
One of the big challenges of the garden is to identify the good guys from the bad guys so that you can gauge how the “war” against the bad guys is going in your landscape. Who are the good guys that wage war on the bad guys in the landscape?
Predators eat other insects. Examples of predators include the lady beetle (Hippodamia convergens), assassin bug (Redruviidaye), damsel bug (Nabidae), big-eyed bug (Lygaeidae) and green lacewing larvae. Two very important groups of predators that that are not insects include spiders and mites. Spiders are very effective predators that are general feeders. They are often destroyed because people fear being bitten. Although many spiders bite humans and other animals, they do so for protection, not for food. Parasitoids are insects that lay eggs in or on other insects, resulting in the death of the host insect. Examples of parasitoids include many wasps such as the Thichogramma wasp (Trichogrammatidae). Without pollinators, fruits and vegetables and the production of seeds would be greatly reduced. The best-known pollinator is the honeybee, but our gardens also benefit from other native pollinators such as bumblebees and mason bees. It is estimated that some 400 different species of bees reside in Virginia. In addition, adult parasitic insects such as small wasps feed on pollen and nectar and are also considered to be pollinators. And let’s not forget butterflies and moths.
The following are just a few of the more common good and bad bugs I encounter each year in my gardens.
The Praying Mantis is one of the easiest insects to recognize and is an indiscriminate predator. You would not guess by looking at it, but the swizzle stick-thin mantis is a voracious eater and is not fussy about what it catches and eats. It uses those “praying” hands to pin down its victim and then shreds it alive with its powerful mouth.
The Assassin Bug is a great example of a creepy-looking bug that is harmless to you (if you leave it alone) and good for your garden. It subdues its prey in a particularly inventive — albeit ghastly — manner. Like a movie hit man, the assassin bug is equipped with a specialty-killing tool. Projecting from its head is a long skewer (the entomological term is “rostrum”) that is part suction tube and part syringe. The assassin bug uses this rostrum to inject a venom which first immobilizes its victim and then liquefies its victim’s insides—which the assassin bug then sucks out!
Ladybug. Everybody loves ladybugs. Both the adult and the larvae eat other insects that we don’t care to have around our gardens. Ladybugs are especially fond of the aphids that like to wreck our Crape Myrtle trees.
The Lacewing Fly is easy to identify because of its long, translucent wings. Adults feed only on nectar, pollen, and aphid honeydew, but the larvae are active predators that eat the eggs and immature stages of many insect pests including aphids, spider mites, and mealybugs
Distinctive strands of eggs are a sure sign that lacewings are on duty in your garden. The lacewing lays its eggs on long threads that seem to sprout from a leaf so that predators can’t eat them.
Damsel Bugs are dull brown, tan, or gray with narrow bodies that measure about ¼” long. Damsel bugs help control aphids, asparagus beetles, cabbage worms, spider mites, and whiteflies, and have been observed feasting on Colorado potato beetle eggs and larvae.
Hover or Syrphid Flies resemble tiny wasps, with a black-and-yellow- or white-striped abdomen. They will hover like a hummingbird as they drink nectar from flowers. Adults range in size from ¼” to ½”. Hover flies are important pollinators and predators. They help control aphids, cabbage worms, and mealybugs. Don’t panic – hover flies are true flies and don’t sting like bees or wasps. They belong in the fly family Syrphidae and some folks refer to them as syrphid flies. Hover flies are the gentle gents of the garden. According to Cornell University, a hover fly larva can consume up to 400 aphids before it becomes an adult fly. They truly are a gardener’s friend.
Parasitoid Wasps range in size from a flake of pepper to nearly 3 inches. They have slender, elongated antennae and are found throughout Virginia. These tiny, non-stinging wasps are know to parasitize over 200 species of pests and may be the gardener’s most important biological control method. Although there are tons of different species of parasitic wasps, they all work by preying upon one or more pest insects. Depending on the species of parasitic wasp, they help rid your garden of: aphids, beetle larvae, bagworms, cabbage worms, Colorado potato beetles, corn earworms, cucumber beetles, cutworms, gypsy moth caterpillars, Japanese beetles, leaf miners, mealybugs, Mexican bean beetles, moth caterpillars, sawfly larvae, scale, squash vine borers, tent caterpillars, tobacco budworms, tomato hornworms, and whiteflies.
Parasitoid wasps are very sensitive to insecticides, so avoid or limit the use of chemical sprays. Most adults feed on plant fluids and sugars, so provide flowering plants that provide nectar sources. The best nectar sources are flowers with wide or shallow corollas that allow the wasps to easily reach nectar; members of the carrot (umbelliferae) and cabbage (cruciferae) families are examples of good nectar sources. Plants with floral nectaries (nectar-producing glands) are also important sources of food, as are aphids and other honeydew-producing sucking insects. Plants that provide shade on hot summer days are a big help to parasitoids. Trichogramma wasps and those that attack scale insects, filth flies, aphids, and other insects can be purchased commercially for release, but it’s important to procure the right species to control the pest you have.
Tachinid Flies (family Tachinidae) are by far the largest and most important group of parasitic flies, with over 1,300 species in North America. All species are parasitic in the larval stage and many are important natural enemies of major pests. Many species of tachinids have been introduced into North America from their native lands to suppress populations of alien pests. Tachinid flies differ in color, size, and shape, but many somewhat resemble houseflies. They usually are gray, black, or striped, and often have many distinct abdominal bristles. Their bodies measure anywhere from 1/3” to ¾”. Tachinid fly larvae attack many different caterpillars, Colorado potato beetles, corn earworms, cucumber beetles, cutworms, Japanese beetles, and squash bugs. Many resemble house flies in size and color. They have robust bodies; are usually gray, black, or striped in color; and have stout, hairy bristles protruding from the tip of the abdomen. The feather-legged fly is bright orange with a velvety black head and thorax; dark legs (hind legs have a fringe of short, black hairs); yellow feet; large, brown eyes; and brown and black wings. Tachinid flies are found throughout the garden and landscape and are frequently mistaken for houseflies. Feather-legged fly is commonly found in the garden laying pale, oval eggs on the side of squash bugs. Istocheta aldrichi, may be seen in lawns and shrubbery attaching eggs to the thorax of newly-emerged adult Japanese beetles. The most obvious sign of tachinid fly activity may the presence of oblong, white eggs glued to the top of the head or body of a host insect. Most adult tachinid flies feed on nectar and pollen, especially from flowering umbelliferous plants such as carrot, dill, and other herbs; composite flowers such as asters and rudbeckias; and other flowering plants. They also feed on aphid honeydew, so having non-crop plants infested with aphids will support tachinid flies.
Ground Beetles. There are hundreds of kinds of ground beetles, and most eat other insects. Both adults and immature ground beetles are predators and they feed on caterpillars, cutworms, root maggots, spiders, snails, slugs, mites, and other beetles. They can be found under logs and debris. Ground beetles are indeed another friend found in our garden.
Starter List of Bad Guys:
Tomato Hornworms are common caterpillars in the garden and landscape. They can be found feeding on tomatoes, potatoes, and eggplants. They are called hornworms because they have a “horn-like” tail. Tomato hornworms are huge caterpillars and will become sphinx moths.
There are many natural enemies of the tomato hornworm. Various general predatory insects such as lady beetles and green lacewings often prey upon the egg stage and on young caterpillars. Another important predator is the paper wasp, Polistes spp. This common wasp feeds on many types of caterpillars, including those found in gardens.
Tomato hornworms are also parasitized by a number of insects. One of the most common is a small braconid wasp, Cotesia congregatus. Larvae that hatch from wasp eggs laid on the hornworm feed on the inside of the hornworm until the wasp is ready to pupate. The cocoons appear as white projections protruding from the hornworm’s body. If such projections are observed, the hornworms should be left in the garden to allow the adult wasps to emerge. When these wasps emerge from their cocoons, they will kill the hornworms and then seek out other hornworms to parasitize.
Cabbage Loopers are another common caterpillar. Cabbage loopers attack cabbages and other members of the cabbage family such as Brussels sprouts, broccoli, and cauliflower. Cabbage looper adults are nocturnal moths with a 1½” wing span. They have mottled, grayish-brown wings with a small silvery white figure 8 in the middle of each of the front wings. Eggs are creamy white, aspirin-shaped and about the size of a pin head. Eggs are easily seen and most often laid on the underside of the lower leaves. The caterpillars are pale green with narrow white lines running down each side. Since cabbage looper caterpillars have no legs in their middle sections, they have a characteristic looping motion as they move across vegetation, giving them the name cabbage loopers. Full grown caterpillars are about 1½” in length.
The cabbage looper has many enemies that are both native to our area and naturally occur in our gardens. These enemies include predators such as paper wasps, and parasitic flies and wasps, e.g., the parasitic wasp, Cotesia glomerata.
Some wasps and flies parasitize the caterpillars while others attack the pupae. As the wasps or flies develop within the caterpillar or pupae, they eventually kill their hosts. Some wasps also parasitize the eggs of these caterpillar pests. These wasp and fly parasites are small and do not sting or bite people.
Aphids. Most mature aphids are about 1/8″ long and are yellow or light green. A few are black, brown, white, grey, or shades of red. Aphids may be winged or wingless. Each aphid has six thin legs, two antennae on the head, a pair of tubes on the back, and a slender “beak” which is pushed into plants to suck sap. Most aphids prefer to feed on buds and the underside of terminal leaves; however, some species are adapted to feed on roots. Aphids are a huge pest on roses, other flowers, vegetables, shrubs, and trees. Enemies include assassin bugs, damsel bugs, ladybugs, spiders, and hover flies.
The Colorado Potato Beetle, Leptinotarsa decemlineata , is a major potato pest throughout North America. It was first recognized as a potato pest in 1859 in Colorado when the beetle switched from its normal host, buffalo bur, a relative of the potato, to cultivated potatoes brought into the region by early settlers. Once beetles began feeding and reproducing on cultivated potatoes, they were able to migrate eastward, feeding on potatoes grown on farms and in gardens throughout the Great Plains and the Ohio River Valley. On average, the Colorado potato beetle expanded its range eastward approximately 85 miles per year, reaching the East Coast by 1874.
Adult Colorado potato beetles are 1/3″ long with hard, rounded wing covers that are black-and-tan striped. The fat, reddish-pink larvae are 1/2″ long, have rows of black dots on their sides, and a small black head. Colorado potato beetles are very common across the U.S., except in the Pacific Northwest and the Deep South. They feed on all members of the tomato family, though potatoes are by far their favorite food. Enemies of the Colorado potato beetle include: assassin bugs, praying mantises, parasitic wasps, tachinid flies, and damsel bugs.
Cucumber Beetle. Both the striped and spotted cucumber beetle is a serious pest in Virginia. Both species measure about ¼” long. Cucumber beetles feed on cucurbits such as cucumber, melon, squash, watermelon, and pumpkin and are considered to be one of the most destructive insect pests of these crops. The striped cucumber beetle may also feed upon asters, roses, potatoes, corn, and peanuts, particularly when cucurbit plants are unavailable. Adult cucumber beetles chew ragged holes in foliage and can completely defoliate and destroy young seedlings. The striped cucumber beetle also can transmit a deadly bacterial wilt and mosaic virus. In addition to leaf feeding, adults can chew the stems, flowers, and rinds of fruit. Predators of the cucumber beetle include assassin bugs, parasitic wasps, tachinid flies and parasitic nematodes.
Mexican Bean Beetle adults are coppery brown with black spots. They look very much like large lady beetles and in fact are closely related, but unlike lady beetles, they feed on leaves, not on other insects. Shortly after adults arrive in the bean patch, they lay yellow-orange egg masses on the underside of bean leaves. These eggs hatch into bright yellow, spiny, oval larvae which feed; molt several times as they grow; and pupate on the underside of leaves. Feeding damage from adults and larvae can reduce yield and injure pods if numbers are high. A parasitoid wasp Pediobius foveolatus has been found to be an effective biological control.
The Japanese Beetle is a major pest of lawns and ornamental plants in Virginia. Adult beetles feed on more than 275 species of plants but especially like plants in the rose family. Grubs (larvae) feed on the roots of turf grasses such as Kentucky bluegrass, fine fescue, ryegrass, and bentgrass.
Bagworm Caterpillars make distinctive 1.5 to 2 inch long spindle-shaped bags that can be seen hanging from the twigs of a variety of trees and shrubs. Sometimes the bags are mistaken for pine cones or other plant structures. Bagworms are perennial pests of juniper, arborvitae, spruce, pine, cedar and other conifer species. They also attack deciduous trees. Female moths cannot fly but the larvae can disperse. Very small caterpillars can spin strands of silk and be carried by wind, an activity called “ballooning.” Larger larvae may crawl to adjacent plants. Bagworms construct protective bags for overwintering and from which young larvae will crawl out next year.
Eastern Tent Caterpillars (Malacosoma americanum) have been numerous and obvious the past few weeks in Iowa. I have noted large numbers of them on ornamental shrubs planted along the interstate highways.
Eastern tent caterpillars make “tents” of silk in the crooks of branches of the tree or shrub they are feeding on. The caterpillars use the tent for protection from weather, predators and parasites and move out of the tent to feed on the leaves during the day. Tents start out very small but enlarge as the caterpillars feed and grow and add to the tents, making them more obvious in the landscape.
Caterpillars feed on the buds and foliage of a variety of trees and shrubs but prefer apple, crab apple, wild plum, cherry, and similar trees.
The Brown Marmorated Stink Bug (BMS) arrived in this county from Asia in the 1990s and has become both a nuisance in the home landscape and a problem for plants. It feeds on many fruits, vegetables, berries, grapes, roses, and more. Presently there are no known native predators. For more information check out our article, “Brown Marmorated Stink Bug,“ in the November 2016 issue of The Garden Shed.
The Diversified Garden
A colony of aphids, cutworms, or squash bugs may appear overnight but it takes time to build up an army of beneficial insects, and this build-up has to start early in the gardening season. The results are not instantaneous but the benefits in the garden are cumulative over time. As the plantings mature and resident populations of beneficial insects become established, the need for chemical pesticides and other aggressive insect control techniques will diminish. One of the gardener’s most difficult challenges is to resist the urge to spray or dust insecticides until the particular pest problem has been identified. Now when I go on patrol in the vegetable garden, I will go armed with a hand lens and an insect reference book. Before I squash that bug between my forefinger and thumb or that egg mass attached to a leaf, I will want to know if it is a foe or a friend. And this is not as easy as it sounds. There are several bad insects that are very similar to beneficial insects. Two that come to mind are the Mexican bean beetle (bad) and the ladybug (good); the brown marmorated stink bug (bad) and the spined soldier bug (good).
Remember what we discussed at the start of this article: In nature there is no such thing as a good bug or bad bug; it’s all about balance. When a pest infestation breaks out and overwhelms our landscape, something has been thrown out of balance. This balance can be attributed to the loss of native habitat (both our friends and foes need a home); non-native (alien) pests being introduced; and the regular use of synthetic, broad-spectrum pesticides that are very efficient in killing beneficial insects and pollinators. In general, using fewer, more controlled chemical solutions results in a more diverse population of beneficial insects. Sometimes in the heat of battle I forget that if we nuke all the bad bugs, there is nothing to sustain the good bugs so that they can attack the next bad bug infestation.
The good bug and bad bug balance can also be negated by the introduction of alien pests that have no native adversaries. The brown marmorated stink bug, the Asian gypsy moth, the emerald ash borer, and the hemlock ash borer are just a few alien pests that come to mind.
An excellent way to attract beneficial insects into your landscape is to provide some elements of a native habitat in and around your landscape. This will improve the abundance and diversity of both pollinators and the natural enemies of pests. A garden with a good diversity of local and native flora will soon attract a good diversity of insects. Check out our article “Insectary” in the April 2015 issue of The Garden Shed.
Often when we think about a pending insect infestation, we overlook a very important component — the plant itself. The first line of defense in warding off a bad bug attack is having a healthy plant. Insects are attracted to a weakened or stressed plant. This weakened condition can be the result of a lack of water and/or a lack of nutrients. A strong, unstressed plant has a greater chance of surviving an insect attack.
Thanks for joining us in The Garden Shed and we look forward to your visit next month.
“Insects as Pests,” North Carolina State University, https://projects.ncsu.edu/cals/course/ent425/text18/pestintro.html“
“Number of Insects (Species and Individuals),” Smithsonian, https://www.si.edu/Encyclopedia_SI/nmnh/buginfo/bugnos.htm
“The Importance of Pollinators,” USDA, https://www.nrcs.usda.gov/wps/portal/nrcs/detail/pa/plantsanimals/?cid=nrcs142p2_018171
“Good Bugs, Bad Bugs: The Insects that Impact the Food We Eat,” Cornell University, http://blogs.cornell.edu/naturalistoutreach/files/2013/09/Good-Bug-Bad-Bug-1l3rl5c.pdf
“Fanatical Botanical: Save the (native) Bees,” The Roanoke Times, http://www.roanoke.com/life/home_garden/fanatical-botanical-save-the-native-bees/article_135ca2bd-8f21-541e-b056-a613b1035a86.html
“Hover flies: Garden Warriors,” University of Illinois, http://news.aces.illinois.edu/news/hover-flies-garden-warriors
“Parasitoid Wasps (Hymenoptera),” University of Maryland Cooperative Extension, https://extension.umd.edu/hgic/insects/parasitoid-wasps-hymenoptera
“Colorado Potato Beetles in the Home Garden,” University of Minnesota Extension, https://www.extension.umn.edu/garden/insects/find/colorado-potato-beetles/,
“Cucumber Beetles,” Virginia Cooperative Extension Publication 2808-1009, https://pubs.ext.vt.edu/2808/2808-1009/2808-1009.html
“Pediobius foveolatus – A parasitoid of the Mexican bean beetle,” Virginia Cooperative Extension Publication ENT 170,https://pubs.ext.vt.edu/ENTO/ENTO-170/ENTO-170.html