Learn Your Bugs: Beneficial Insects Can Help Control Garden Pests

June 27, 2001

COLUMBUS, Ohio - Garden lovers looking for a more natural way to control ornamental pests other than using insecticides may have to look no farther than their own backyard.

Predacious insects, also referred to as beneficials, can make quite a meal of garden pests as long as they are provided a suitable habitat and ample food and water, said Barb Bloetscher, an Ohio State University Extension entomologist.

"In order for a beneficial to stay in someone's landscape, it needs food, water and shelter," she said. "And you have to allow for the pest population to build up in high enough numbers for a beneficial to stick around. Which means keeping insecticide applications to a minimum."

So how does one separate a good bug from a bad bug? Know your insects, said Bloetscher. "There are tons of books available and lots of websites that explain beneficial insects," she said. "One doesn't have to be an insect expert in order to recognize the more common beneficials."

Predacious insects do exhibit some characteristics that help to separate them from other bug groups. They are usually solitary creatures; they either actively hunt for their prey or camouflage themselves and wait for prey to come to them; and they have mandibles, or piercing mouthparts, which could be considered fangs in animals.

For example, true bugs, like the ambush bug and assassin bug, have piercing mouthparts and sneak up on their prey. The aphid lion, larva of the green lacewing, actively hunts and attacks its prey by seizing it with large, sickle-shaped mandibles and injecting a paralyzing venom. The praying mantis and spiders, on the other hand, lie in wait and snatch up any unlikely prey that happen to cross their path. Names -- such as minute pirate bug, spined soldier bug, and ant lion -- also help reveal an insect's true nature.

But insects don't make it easy to weed out the good from the bad. Predacious insects come in all shapes and sizes, sometimes disguising themselves as the pest they are targeting. Bloetscher said a mealybug destroyer, a ladybug species, looks just like the mealybug, a small, white, soft bodied, cotton-like insect that sucks sap from a plant. Even a predacious insect's appearance, in both adult and larval form, can be odd, if not fearsome, and hence may be labeled a "bad" bug.

Bloetscher said the larvae of most predacious insects are more beneficial in controlling insect pests than the adult stage. And it's the larval stage that people know the least about since most larvae look nothing like the adults.

Most predacious insects will feed on aphids, spider mites, leafhopper nymphs, thrips, ants and scales. Other insects, such as spiders and praying mantids, are not quite so selective and will feed on other beneficial insects, as well as pests. Predacious insects run the gamut from ground beetles to parasitic wasps.

Probably the best-known predacious insect is the ladybug, or ladybeetle. "The ladybug has been getting a bad rap because of the multicolored Asian ladybug, which is the beetle that finds its way into people's homes," said Bloetscher. "But our native ladybug is not a pest like the Asian ladybug is."

There are thousands of different ladybug species, of which there are plenty of variations in size and color. "There are some with spots, some with no spots, and they range in color, from red, black, orange and yellow," she said.

Bloetscher said there is a move toward organic gardening. "People don't want to use chemicals," she said. "They can cut down on insect pests by planting smart and learning what beneficials they have in their landscape."

For more information on beneficial insects, log onto Ohioline's website at http://www.ag.ohio-state.edu/~ohioline/lines/pests.html#PST.7.

Author(s): 
Candace Pollock
Source(s): 
Barb Bloetscher