Spring Fever: Restless Brown Marmorated Stink Bugs Stumble Forth

Halyomorpha halys is the brown marmorated stink bug (BMSB), a name which is usually simplified to stink bug. Native to mainland eastern China, Japan, Korea, and Taiwan, these insects are in the family Pentatomidae (Greek: pente “five” + tomos “section”). This family is so named because their antennae have five segments.

Halyomorpha halys slipped into the United States sometime in the 1990s, probably in shipping crates. Sightings were first reported by college students at Muhlenberg College in Allentown, Pennsylvania in August 1998. The first collection of a specimen occurred in Allentown the next month, September 1998. In all likelihood the first sightings did not constitute the first appearance.

The introduction, albeit accidental, has mushroomed into an invasion. As of September 2010, BMSBs have been noted in 37 of Pennsylvania’s 67 counties. Nevertheless, the Pennsylvania State University College of Agricultural Sciences considers it “probable that they are in all counties” (Steve Jacobs, April 2011).

What BMSBs look like

Adult BMSBs are about two-thirds of an inch (17 millimeters) in length.

Their typical shield shape makes their width almost equivalent to their length.

Their antennae, which are in five segments, are black with a white band.

Their underside is pale while the shield part of their body is mottled brown-grey.

Alternate bands of black and white on the laterotergites (abdominal flanges) protrude around the wings, along the lower sides of the dorsal shield, from behind their back legs almost to the membrane, the bug’s pointed tip.

Its generally dark legs are banded in faint white.

Instars: five stages from egg mass to adult

Halyomorpha halys goes through five nymphal stages, called instars, in their growth from newborn to adult. Length through the stages ranges from 0.1 inches (2.4 millimeters) to about 0.5 inches (12 millimeters).

Instars, which are brightly colored, are more vulnerable than adult BMSBs, which, with their barklike coloring, disappear into their surroundings. Instars have dark reddish eyes. Their yellowish-red abdomen has black striping.

Nevertheless, their legs and antennae, with their black and white banding, resemble those of the adult.

Why they are called stink bugs

The unflattering epithet is derived from the pungent odor that is emitted by the scent glands of Halyomorpha halys. The stench is a defense mechanism to dissuade birds and lizards from devouring them, but BMSBs sometimes release the malodor when they are being touched, moved, or squished.

Proliferation factors

Without any known natural enemies in the United States, BMSBs proliferate easily and remain unvanquished.

Unseasonably warm seasons, as occurred in Pennsylvania in 2010, promote the development of two or three generations, instead of the normal one generation per year. In contrast, four to six generations per year are recorded in subtropical parts of China. As Penn State entomologist Steve Jacobs observed:

“. . .this year’s warm spring and early summer allowed the stink bug to reproduce at a faster pace. Normally, you’d see one generation of stink bugs per growing season, but this year, we’ve had three generations, leading to higher and faster-spreading populations.”

Decimation by pesticide/insecticide application is not recommended for many reasons. Importantly, these compounds do not evince significant residuality, which means that immigrants after spraying are unaffected and therefore rapidly repopulate.

The brown marmorated stink bug population is controlled in Asia by a natural enemy, a parasitic wasp that attacks stink bug eggs. Introduction of this natural control from Halyomorpha halys’ native region in Asia into their naturalized range in the United States entails a lengthy process of quarantine and study and may not prove desirable or viable.

Favorite foods

It is estimated that BMSBs gorge on 300 host-plant species that range from apples and peaches to blackberries to corn, lima beans, green peppers, soybeans, and tomatoes.

Cat-facing insects

Cat-facing insects such as Halyomorpha halys cause “unsightly dimpling, deformity, and scarring” by feeding on the surface of crops, especially fruits.

“The name ‘cat facing’ comes from the distorted fruit shape that resembles the puckered cheeks of a cat.” (Diane Alston et al, October 2010)

Cat facing occurs because of their piercing-sucking style of feeding. Piercing the skin of the crop with their mouthparts, they then inject saliva and suck out the juices. Although their direct contact with the crops and the salivary orts that they leave apparently are innocuous to humans, the external injury as well as the internal dehydration prohibit marketability as produce. Damaged fruit can be downgraded for processing as juice, for example, but the sale price drops dramatically to one-third to one-tenth of the value that is achieved with whole, undamaged fruit.

BMSBs are considered to be serious agricultural pests, attacking crops vigorously in mid-summer to early fall (July to September) as the crops near maturity. The Mid-Atlantic region has expressed concern over damage to crops from marauding brown marmorated stink bugs.

BMSB lookalikes

The term “stink bug” is not exclusive to BMSBs. It is applied to similar looking, native species. BMSBs are differentiated from lookalikes by the black and white banding on their abdomen along the wings, by their white-striped antennae, and by their speckling.

Homesteading cycle

From September through mid-October, adult BMSBs search for their winter lair. Popular overwintering sites for them are inside homes, where they snuggle invisibly for the cold months.

Spring fever

In late April to mid-May adults emerge, somewhat sluggishly, from their hiding spots. Spring is in the air, and they have spring fever. They are anxious to shake off winter’s inactivity, to identify plentiful food sources, and to think about upcoming mating and depositing eggs, which occupies them from May through August.

BMSBs are being seen increasingly as spring progresses. Just as they are responding to spring’s siren call, so all of the rest of nature, in its floral and faunal forms, is awakening. Of particular interest to BMSBs are the floral rebirths and renewals, for therein lies their food supply.

Inside homes or outside, Halyomorpha halys adults are restless and hungry, and they are throwing caution to the wind. They do not seem to care who sees them at this time of year.

Alston, Diane, Michael Reding, and Marion Murray. “Cat-facing Insects.” Fact Sheet Series:  Insects – Tree Fruit. Utah State University Extension and Utah Plant Pest Diagnostic Laboratory, October 2010. http://extension.usu.edu/files/publications/factsheet/cat-facing.pdf

“How to Identify the Brown Marmorated Stink Bug.” Rutgers New Jersey Agricultural Experiment Station. http://njaes.rutgers.edu/stinkbug/identify.asp

Jacobs, Steve. “Brown Marmorated Stink Bug: Halyomorpha halys.” Penn State Fact Sheet. Pennsylvania State University College of Agricultural Sciences. Updated April 2011. http://ento.psu.edu/extension/factsheets/brown-marmorated-stink-bug

Maguire, Ken. “Move Over, Bedbugs:  Stink Bugs Have Landed,” The New York Times, September 26, 2010.

“Researchers Seek Elusive Answers to Stink-Bug Infestations.” Penn State Fact Sheet. Pennsylvania State University College of Agricultural Sciences. September 29, 2010. http://live.psu.edu/story/48793

My special thanks to talented photographers who make their fine work available on the internet:

* David R. Lance, U.S.D.A. APHIS Plant Protection and Quarantine Program, for “Brown marmorated stink bug adult” (September 5, 2005)

* Pennsylvania Department of Conservation and Natural Resources – Forestry Archive for “Halyomorpha halys (adult); family Pentatomidae” (March 19, 2008)

* Gary Bernon, U.S.D.A. APHIS for “Hatching Halyomorpha halys” (March 21, 2008) and for “Brown marmorated stink bug (Halyomorpha halys)(adult) on a peach (Prunus persica); family Pentatomidae” (March 21, 2008)

* Rutgers New Jersey Agricultural Experiment Station for “First Instar,” “Fourth Instar,” and "Photo of an adult brown marmorated stink bug with white stripe on antennae and black and white banding on abdomen highlighted"

Copyright Tuesday, April 18, 2011 by Derdriu