Yet another invasive insect.

I've written before about the impact of the Emerald Ash Borer on forests in southwestern Ohio.  My introduction to the pest I'm profiling this time came last summer when I found my tomato, pumpkin, cucumber, acorn squash, watermelon, and summer squash vines infested with a strange brown bug with an oddly shaped abdomen: Halyomorpha halys (Stål), the brown mamorated stink bug.

Picture from http://www.stopbmsb.org/stopBMSB/assets/Image/BMSB-on-bark-istock350w.png

If you're like me, you've found these bugs everywhere over the past year—especially in your house over the past winter.  The biggest question I've been asked beyond "What is it?" is "How do we get rid of it?"  The answer?  Well, at this point, we don't—all we can do is keep them out of houses.

Native to Asia, these bugs feed on a variety of trees, ornamental plants, and crops.  This generalist feeding strategy is what makes them so problematic outside of their natural range.  They impact a wide variety of species, making their impact harder to detect and harder to control.  So far, they are known to feed on 170 species of trees, shrubs, vegetables, and crops in North America, including several other invasive species such as the invasive tree species Tree-of-heaven (Ailanthus altissima) or Russian olive (Elaeagus angustifolia), both also from Asia.  Unfortunately, most of the tree species I study are on that list, especially the maples (Acer sp.), as are several vegetables I grow.  Fruit farms have been especially hit hard, with some growers reporting total losses.

So how did they enter North America?  No one really knows.  What is known is that they were first found in Allentown, PA, in 1996.  They have spread explosively from that origin and are now found in 40 of the 50 states.

Map from http://www.stopbmsb.org/where-is-bmsb/state-by-state/
Given the distribution, H. halys is likely in several other states (Oklahoma, Arkansas, Lousiana, Nevada, Colorado) but just haven't been detected yet.

What's the impact on natural ecosystems?  Quite frankly, no one knows yet.  Given the wide variety of species targeted, showing significant impacts in the wild will be difficult.  The only impacts that have been noticed so far are impacts to fruit farms and crops and the annoyance of finding stink bugs in buildings.  H. halys overwinters in leaf litter and inside buildings, sometimes by the thousands as was the case for one Maryland homeowner.  Controlling H. halys invasions of a building usually means sealing cracks in the building so the insects cannot get in, treating vegetation around the building with insecticides, and/or using foggers and sprays to kill those inside the building (more information here).

Control options for farmers and gardeners are limited.  H. halys is fairly insecticide-resistant, with only two commercial insecticides known to be effective and only approved on an emergency basis.  Organic farmers are at a particular disadvantage, with only one organic insecticide available—and it's not really known yet if that particular insecticide is effective.  With no real natural enemies here in North America, there is little to control their population size and spread.  Biological control research for this pest is in its infancy.  There is a parasitoid wasp in Asia which preys on H. halys eggs as well as a fungus from Japan but much more research will need to be done before either is a viable option in North America.  The big question is whether or not those potential biological controls will attack other North American species if released here, especially our native stink bugs.

As for the future, expect H. halys to stick around.  The cold winter in North America that we just endured may knock their numbers down a bit but like other insect pests (i.e. Emerald Ash Borer), it won't be enough to destroy them.  Their native range in Asia already includes cold climates, so H. halys is well adapted to surviving cold winters.  And in a warming world where winter temperatures have risen faster than other times of the year, winters cold enough to depress insect populations are becoming sporadic.  That's bad news for plants, as warmer winters means insect populations will be higher in the spring leading to greater insect damage throughout the the growing season.

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