Mortality of stink bugs was high in my brother’s unheated garage.
Bug of the Week returns from tropical adventures where we last met wonderful insects such as treehoppers, tarantulas, army ants, and morpho butterflies. This week the news was replete with stories of the home invading Brown Marmorated Stink Bug (BMSB) suffering a major beat-down administered by the wicked winter weather of 2014. In previous episodes, we met this native of Asia that first appeared in the United States in the middle 1990’s near Allentown, PA and is now found in more than 40 states from coast to coast, border to border.
Brown marmorated stink bug nymphs suck the juices from an unfortunate gardener’s tomato.
This stinker has caused significant losses to peaches, pears, and apples with regional losses to apples in 2010 exceeding 37 million dollars. Organic vegetable growers, community gardeners, and homeowners have also been vexed when hordes of stink bugs lined ripening tomatoes, poked holes in the skin, and then drained the juicy tissues below, leaving speckled, puckered, and pockmarked fruit. We have also learned in the last few years that BMSB dine on more than 150 different varieties of trees and shrubs used in landscape plantings. In autumn, they move to tree trunks and plunge their beaks through the tree bark to extract nutrients from underlying tissues. This insult creates weeping wounds and the sugary exudates attract a variety of disagreeable stinging insects, including paper wasps and yellow jackets.
For many visitors to Bug of the Week, stink bugs in apple orchards or corn fields probably seem like a remote problem. However, the nuisance potential of BMSB is almost without equal. After the autumnal ravaging of crops and trees, these stink bugs seek shelter in homes. This pending assault 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. Why do stink bugs enter homes and man-made structures in the first place? Many folks incorrectly believe they enter to be warm for the winter. Bear in mind that millions of years ago when BMSB evolved, there were no mansions or man-made structures to invade. In chilly locations where winter halts the growth of deciduous trees and shrubs and withers herbaceous plants, food for the plant-eating stink bug all but disappears. Cold temperatures slow their movement and bring their development to a standstill. During this inimical season, BMSBs seek refuges under the bark of dead trees and other landscape features to chill-out, protected from the harsh weather and dangerous predators.
Chances are good that hemlock woolly adelgid took a beat-down in cold locations along the Appalachians.
Insects that overwinter in temperate climes have evolved clever strategies to withstand the cold. One such strategy is to produce cryoprotectant chemicals such as glycerol that prevent the formation of lethal ice crystals within the insect’s cells. These chemicals act much the same way as the anti-freeze added to the radiators of cars. How clever! But these cryoprotectants can only stop cells from freezing to a certain point. As record cold arrived in January in the form of the Polar Vortex, we began to hear reports that bone-chilling temperatures may have put the kibosh on many insect pests. There is good evidence that pests such as the hemlock woolly adelgid, mimosa webworm, gypsy moth, and even the dreaded emerald ash borer may have suffered significant mortality in the icy grip of Mother Nature’s arctic blasts.
Temperatures of –25 to –30 degrees Fahrenheit in Minnesota may have killed emerald ash borer larvae beneath tree bark.
A few weeks ago, researchers at Virginia Tech discovered that BMSBs wintering in artificial shelters outdoors experienced mortality a.k.a “kill rates” in excess of 90%. This prompted media sources and the public to wonder if BMSBs would be extirpated at best or diminished at least as a result of the frigid weather. The short answer to this is that it is simply too early to tell how significant the carnage has been. On several days in January, temperatures in Blacksburg, VA reached - 5 degrees Fahrenheit and cold of this magnitude proved lethal to BMSBs in this study. Other scientists in West Virginia found kill rates in the order of roughly 50% for collections of BMSBs that overwintered outdoors. In addition to the depth of cold experienced by overwintering BMSBs, the quality of their refuge also is likely to affect their survival. Each day for the past several weeks, I have noticed stink bugs wandering about my desk or ascending the windows in my living room. Clearly, my home and many others provided sufficient refuge for BMSB to escape the thermal massacre. Scientists also believe that the nutritional status of stink bugs entering the winter may affect their survival. Those well fed with sufficient fat reserves may be more likely to survive than those with insufficient reserves.
The reality is this; we simply lack sufficient information to accurately predict how record cold in many parts of the BMSBs range in the US will affect the status of the pest in spring and summer. Scientists throughout the land are pursuing answers to this and many other mysteries of BMSB. But as Mother Nature sends another snowy blast to the mid-Atlantic this first week of March, perhaps we can be cautiously optimistic for the arrival of a spring with fewer stink bugs than we have seen in recent years. Time will tell.
In protected locations like boxes stored in my attic, stink bugs survived the Polar Vortex.
References
We thank Tom, Tracy, Ivan and several members of the media for proving inspiration for this week’s episode. To learn more about BMSB and the Polar Vortex, please click on the following links: