June 16, 2004 | By: Ellen Brightwell
LEXINGTON, Ky.

“Ugh. Look at those ugly bugs on that plant. Better go get the insect spray.”

Don’t reach for the spray can so fast. What if those bugs are beneficial insects that do good things in the garden, like eat the bad bugs that chew on the plant?

“The term ‘beneficial insect’ applies to species whose predatory or parasitic activities provide a direct benefit,” said Ric Bessin, Extension entomologist with the University of Kentucky College of Agriculture.

“Without beneficial insects, it would be impossible to grow and maintain gardens without plants being overwhelmed with insect pests,” he said. “These ‘beneficials,’ or ‘good bugs,’ are a cheap, constant source of insect pest control, and often reduce the need for insecticide use. Beneficials also pollinate flowers, vegetables and crops, help decompose organic matter in compost piles and are members of wildlife food chains.”

Bessin said many insects people notice in late summer are beneficials whose populations have grown from feeding on pests during the season.

“We need to encourage beneficials, because without these resources we would be plagued with insect pests throughout growing seasons,” he said. “It’s as important to identify beneficials as it is to recognize insect pests. The local Extension office can help you make the distinction before you apply an insecticide.”

Green lacewings, most lady beetles, spiders, praying mantids, parasitic wasps and bees are among the beneficial insects in Kentucky, according to Bessin.

Although green and brown lacewings inhabit Kentucky, the green ones are by far the most often encountered.

Lacewings are among the most important predatory insects because they feed on many soft-bodied insects such as aphids and mites. Adult lacewings have golden eyes, lacy wings, green (or brown) bodies and are about three-fourths inch long. Larvae are brown and white and resemble tiny crocodiles with sickle-shaped jaw bones.

Because they feed on pest eggs and larvae and soft-bodied species, most lady beetles are the first line of defense against many common pests. Sometimes called “ladybugs” or “ladybug beetles,” adults are red or orange with black or brown spots. Larvae usually are brown or black with orange, red or tan makings and look like very small alligators.

“However,” Bessin said, “the Mexican bean beetle is a pest of bean crops and sometimes vegetable gardens. Adults are brown with three rows of eight black spots on wing covers. Unlike other lady beetles, larvae are bright yellow with black branched spines.”
Spiders capture flies and moths that land in their webs. These beneficial arthropods do not feed on or harm plants.

The term “mantid” refers to the whole group of “praying” beneficial insects. Only some praying mantids belong to the “mantis” genus, according to Bessin.

“Mantids are very efficient, deadly predators that capture and eat a variety of insects and other small pray,” he said. “Their camouflage colors enable mantids to blend into the background while waiting on twigs and stems to ambush prey. While hunting, mantids fold their two front legs under their heads in a ‘praying’ position, then use these legs to strike out and capture prey.

“Broad-spectrum insecticides drastically reduce the number of mantids in the garden. To encourage them, use selective insecticides that contain Bacillus thuringiensis and insecticidal soap, and allow some vegetation to grow to provide cover for mantids,” Bessin said.

Some insects have a dual role as beneficials and pests, according to Bessin.

“Honeybees pollinate many food crops, flowers and vegetables that bring us pleasure,” he said. “However, they become a pest when nests are disturbed and guard bees attack unsuspecting people. These stings are a serious threat to people with allergic reactions. The Asian lady beetle devours aphids and scale in our gardens in the summer, but is considered an indoor pest during the fall and winter. Black swallowtail butterflies are prized in the garden. Yet, they are adults of the parsley worm that feeds on carrot and parsley tops."

Beneficial insects are a valuable environmental resource. Without them, we would be plagued with insect pests just about every day this time of year. So think twice before spraying unidentified insects; you might be eliminating ‘good bugs.'

Contact: 

Writer: Ellen Brightwell 859-257-4736 ext. 257
Source: Ric Bessin 859-257-7456