BY MARY JO GIBSON
PENN STATE EXTENSION MASTER GARDENER OF COLUMBIA COUNTY
As much as I love bugs, I admit that many are unwelcome when they invade our homes. Bugs that make offensive odors are high on everyone’s list of undesirable guests. Just the name “stink bug” makes them sound objectionable. However, what is a stink bug?
Well, if it is dark brown, long, slender and tiptoes along, then that stinkbug is really a garden millipede. These thousand-leggers coil for protection when frightened. Sometimes they give off a powerful scent that contains cyanide for protection from predators. Only an inch or so long and less than one-eighth inch thick, these small creatures are commonly found under rocks and flower pots. They usually feed on dead and decaying plant material.
Occasionally, they are greenhouse pests that feed on seedlings. While harmless, millipedes may migrate into our homes during times of drought or excessive rainfall. Because they require high levels of moisture to respire, they usually die before they wander too far indoors. The best treatment is simply to sweep them away. If your home is under siege and feel that you must do something, a perimeter spray of insecticide or food grade diatomaceous earth dust controls millipedes.
What other stinkbugs are there? The true stink bug, correctly written as two words, is a shield-shaped insect of the insect order Hemiptera. Its relatives include cicadas, bed bugs, assassin bugs, leafhoppers and aphids. Stink bugs have piercing-sucking mouthparts that they use to feed.
They are less than one inch long and about two-thirds as wide, in some shade of brown or green. Stink and shield bugs have been in North America for thousands of years; some are good and some are bad. The good ones, like the spined soldier bug, feed on other insects, especially pests. The bad ones feed on plants, especially our crops.
So, what’s the big deal? About 20 years ago, a sharp-eyed master gardener found a different species of stink bug in Lehigh County. This brown marmorated stink bug from Asia is dark, mottled brown. It is a little over a half-inch long, roughly the size of a dime. The last two antennal segments have alternating broad light and dark bands. The exposed abdominal edges also have alternating dark and light banding. They winter inside our homes, unlike our native stink bugs that spend winters outdoors under leaves and mulch. When the brown marmorated stink bugs share our homes, they do not bite our pets or us. They do not feed. They do not make a nest. They are not mating and they are not laying eggs. They do not cause any structural damage. They do not transmit any disease. They are just passing the winter with us. Unfortunately, they are giving off an aggregation pheromone that attracts males, females and nymphs. From their point of view, if one is good, more is better. Nuisance is an understatement.
However, they are much more than a stinky and annoying winter houseguest. The brown marmorated stink bug, Halyomorpha halys, is a voracious eater that damages fruit, vegetable and ornamental crops at other times of the year. Stink bugs feed by injecting their saliva to digest the plant material. While not harmful to people, this feeding method leaves a fruit with dried, corklike areas. Apples may be beautiful when picked, but shortly afterward, damaged spots appear and the fruit is no longer marketable as fresh produce. By 2010, the commercial growers suffered great economic losses due to brown marmorated stink bugs (BMSB). Home growers are devastated when stink bugs feed on their beloved tomatoes and peppers.
From June to August, female brown marmorated stink bugs lay clusters of 20-30 light green, elliptical-shaped eggs on the undersides of leaves. They usually produce one or two generations per year in our area. Newly hatched nymphs are yellowish, mottled with black and red. Older nymphs are darker with banded legs and antennae, like the adults. When disturbed or squashed, the bugs produce their characteristic unpleasant odor.
What can you do? Mechanical exclusion is the best method to keep all kinds of bugs from entering homes and buildings. Caulk cracks and openings everywhere. Repair or replace damaged screens on doors and windows. Use a vacuum cleaner to remove live or dead stink bugs, but be aware that the vacuum may take on the smell of the insects for a while. Most pesticides will not stop a home infestation, so we do not recommend that homeowners apply insecticides to kill stink bugs indoors. Some aerosol sprays and foggers are labeled for stink bugs, but they will not prevent more insects from emerging from cracks after the room has been aired out.
Brown marmorated stink bug traps are on the market. Some use pheromones, while others use blue or ultra-violet light to attract and trap the pests. These are useful for monitoring the outdoor population of stink bugs but may do little to reduce the population significantly. Some consumers think that indoor traps are successful when placed in suspended ceilings and attics. At least they do prevent a few stink bugs from buzzing around our reading lamps and televisions.
Broad-spectrum insecticides are effective for commercial growers, but they kill the beneficial insects also. This upsets the balance that growers try to achieve with integrated pest management and causes other pests to flourish.
As with most introduced species, our habitat lacks the natural predators and diseases of brown marmorated stink bugs. Researchers are studying tiny parasitic wasps that attack BMSB eggs. It takes time to determine the effects these parasitoids will have. There has been success planting a trap crop of sunflowers — a real BMSB magnet. Use a portable vacuum cleaner to suck the stink bugs from the sunflowers, then drop them into soapy water. The gentler insecticides like azadirachtin (neem oil) and pyrethrins are somewhat effective for home gardeners.
(Mary Jo R. Gibson has been a Penn State Extension Master Gardener of Columbia County since 2003.)