With the passing of the autumnal equinox last week, it’s time to turn our attention to the home invasion of stink bugs that has become a stinky annual tradition throughout much of the country. Brown marmorated stink bugs (BMSB) now occupy 44 states and four Canadian provinces in North America. In recent years they have also turned up in several European countries including Lichtenstein, Switzerland, France, Italy, Germany and Hungary. On warm afternoons last week dozens of stink bugs decorated fruits of a redbud tree in my yard and leered through my window screens. Why are stink bugs on the move?
For the past several month, stink bugs have been fattening up on corn, soybeans, garden vegetables, and fruit. But soon this cornucopia of earthly delights will disappear for BMSB and other herbivorous insects. In temperate locations like Maryland, winter halts the growth of deciduous trees and shrubs and withers herbaceous plants. Food for the plant and fruit-eating stink bugs all but disappears. With the arrival of cold weather, stink bug movement slows to a crawl and their development grinds to a halt. Prior to this inimical season, stink bugs seek refuge to chill-out where they will be protected from harsh weather and dangerous predators.
In the waning days of summer, stink bug nymphs fatten-up on delectable vegetables like this tomato.
Why do stink bugs enter homes and man-made structures? Many folks incorrectly believe these home invasions provide warm winter refuge for stink bugs. Bear in mind that millions of years ago when these creatures evolved, there were no mansions or man-made structures to invade. Until recently, the natural winter redoubts of these stinkers were largely unknown. However, a clever study revealed large, freshly deceased but still standing trees are a prime winter hideout for stink bugs in natural settings. The loose bark of these trees affords a fine location for stink bugs to crawl underneath and escape the ravages of winter. Rocky ridge tops can provide many dead trees and abundant places for stink bugs to chill-out.
Loose bark, rock crevasses, and homes provide overwintering refuge for the brown marmorated stink bug.
For many viewers of Bug of the Week, stink bugs on rocky ridge tops seems like a remote problem. However, the nuisance potential of BMSB is almost without equal. To a stink bug, a home provides a wonderful assortment of overwintering opportunities beneath siding, behind shutters, and in attics. The pending invasion some homeowners face is no trivial matter. In 2011, a homeowner in western Maryland captured more than 26,000 BMSBs from January through June as they moved about his home seeking egress from their overwintering refuge. Yikes!
While populations of BMSB continue to remain relatively low in Maryland compared to numbers seen a decade ago, to the south and west BMSB continues to be a major pariah. Why do populations of BMSB fluctuate so dramatically from year to year and place to place? Scientists at Virginia Tech and the USDA’s Appalachian Fruit Lab have evidence that visits from polar vortices in the winters of 2014 and 2015 put a beat-down on overwintering BMSB in our region. Fascinating studies at the University of Maryland suggest that our smoking hot summers kill some of the gut microbiota critical to the normal growth and development of stink bug nymphs. Mounting evidence from several universities and government laboratories in our region suggests that indigenous and introduced predators and parasites may be catching up with stink bugs and levying a toll on their populations (see Death of a stink bug, Part 1, Part 2, Part 3, and Part 4). My money is on the possibility that all of these factors, and perhaps some still unknown, conspire to reduce stink bug numbers in our region.
Assassin bugs, including the fierce wheel bug, are part of Mother Nature’s hit squad putting the beat down on invasive stink bugs.
To learn how to keep BMSB out of your home and what to do when they get in, please watch the following video: https://www.youtube.com/watch?v=0kG-2fetbZA
Bug of the Week thanks Doo-Hyung Lee, Doug Inkley, Tracy Leskey, Galen Dively, Tom Kuhar, Chris Taylor, Paula Shrewsbury, and other members of the BMSB Working Group for providing information and inspiration for this episode. Interesting studies including one by D. B. Inkley “Characteristics of home invasion by the brown marmorated stink bug (Hemiptera: Pentatomidae)” were also consulted. Support for our research and outreach on BMSB comes from USDA-NIFA SCRI Award #2011-51181-30937.
To learn more about BMSB biology, distribution and management, please visit the following web site: Stopbmsb.org