Category Archives: Shrubs

2018 Update: Brown Marmorated Stink Bug in Wisconsin

One of the most concerning invasive insects to appear in Wisconsin in the last decade is the brown marmorated stink bug (Halyomorpha halys).  This Asian species delivers a double-whammy of not only damaging crops and other plants, but also being a significant nuisance when it sneaks into buildings in the fall. Since its initial detection in the state in 2010, populations of this insect have built up slowly but steadily. 

Brown marmorated stink bug adult on the side of a building in fall. This is becoming a common site in some parts of the Midwest. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab.

What’s the current status of BMSB in Wisconsin?

As of late 2018, 27 counties have confirmed reports of the brown marmorated stink bug and a handful of other countries have suspected sightings.  This insect has a strong foothold in the state and was confirmed in seven new counties in 2018 alone—Eau Claire, Jackson, La Crosse, Marquette, Monroe, Richland, and Trempealeau counties. 

Distribution of the brown marmorated stink bug in Wisconsin as of late 2018. BMSB has been confirmed in 27 counties. Map Credit: PJ Liesch, UW Insect Diagnostic Lab.

Two core areas currently stand out for brown marmorated stink bug activity in Wisconsin: the Highway 41 corridor from Fond du Lac up to Green Bay and southern Wisconsin from Dane and Rock Counties east to the Milwaukee metro area.  These two areas have the longest history of BMSB in the state and account for the majority of reports thus far. 

Much of the state has yet to encounter this insect or truly experience its impacts.  When the brown marmorated stink bug is first detected in an area, there’s a proverbial “calm before the storm”.   The pattern observed in the state thus far has been a few “quiet” years where low initial populations of this insect result in only a few sightings annually.  However, after a few years in a given area, BMSB populations build up to the point where nuisance problems around structures are noted and reports of potential plant damage begin to trickle in.

What’s the Outlook for BMSB?

Unfortunately, Wisconsin has yet to see the full impact of this invasive insect.  Observations over the last few years have found that BMSB is able to survive our winters and reproduce in the state, so this adaptable pest will most likely continue to build its numbers in the coming years. 

Over time, the brown marmorated stink bug is likely to emerge as one of the top structure-invading pests in the state alongside the likes of boxelder bugs and multicolored Asian lady beetles.  In the eastern US, where BMSB has been established for over a decade in spots, problems can be significant.  In some cases these malodorous insects have been documented invading homes by the tens of thousands

Several brown marmorated stink bug juveniles on a dogwood shrub. Ornamental trees/shrubs, vegetables, and fruit crops can all be attacked by this insect. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab.

While widespread crop damage has not yet been observed in Wisconsin, it may only be a matter of time as population of this insect continue to build in the state.  Agricultural problems have also been significant in the eastern US, giving us a glimpse into what could potentially happen in coming years.  For example, brown marmorated stink bug caused $37 million dollars in losses to apples in the mid-Atlantic states in 2010 alone.  

Having been detected in Portage County in 2017, brown marmorated stink bug may soon start to pose a threat to vegetable production in central Wisconsin.  Similarly, specimens confirmed from Door County in 2017 are forcing fruit growers in that part of the state to keep a close watch on their orchards and vineyards.  With the recent detection of BMSB in several western Wisconsin counties, we’ll likely see BMSB populations slowly build in that part of the state over the next few years as well. 

What should you do?

The “New” Japanese Beetle in the Midwest

Move over Popillia japonica, there’s a new “Japanese beetle” in town.

As is typical in a given year, Wisconsin sees a few new invasive species in the state each year.  In 2016, one of the surprises was the arrival of the “two banded Japanese weevil” (Pseudocneorhinus bifasciatus), often simply called the “Japanese weevil”.  Weevils themselves are technically a type of beetle from the hyper-diverse family Curculionidae, which contains a plethora of weevils, curculios, and multitudes of bark beetles.  When talking to the public, it’s amazing how often the Japanese beetles feeding on landscape plants during the summer are mixed up with the Asian lady beetles (Harmonia axyridis), which invade homes in the fall.  Given the name of this new “Japanese weevil”, I’m expecting this creature to confuse the situation even more.

What is the Japanese Weevil?

The Japanese weevil (P. bifasciatus) is a non-native beetle that feeds on a wide variety of landscape plants, particularly shrubs.  Adult Japanese weevils are ~ ¼” long with a gray or brownish, pear-shaped body with black bands across the wing covers (elytra).  The pale larvae (grubs) live in the soil and feed on roots of suitable host plants.  We haven’t had this pest in Wisconsin long enough to fully understand the local life cycle, but given the pattern in other states, this insect will most likely complete one generation per year, with adult presence and feeding damage occurring during the summer from late June through August.

Photo Credit: Michael C. Thomas, Florida Department of Agriculture and Consumer Services, Bugwood.org
The invasive two banded Japanese weevil (Pseudocneorhinus bifasciatus). Photo Credit: Michael C. Thomas, Florida Department of Agriculture and Consumer Services, Bugwood.org

Where’s the Japanese weevil from?

Very similar to the Japanese beetle (Popillia japonica), the Japanese weevil is native to Japan and first popped up in the US in 1914, via the transport of infested nursery stock.  Like the Japanese beetle, the Japanese weevil feeds on a wide range of landscape plants.  When it first showed up in Wisconsin in 2016, the Japanese weevil was found on a variety of ornamental plants in Madison, WI.  How this species got to Wisconsin remains a mystery, but the movement of infested potted plants is the most likely explanation, as this insect is not capable of flight.  While the Japanese beetle is common across many parts of eastern North America, the Japanese weevil has a much more scattered distribution and can be found primarily in the Mid-Atlantic region with scattered cases in the Illinois, Iowa, Wisconsin and Oklahoma.

What does this insect mean for Wisconsin?

Luckily, it seems that the Japanese weevil may not be nearly as big of a threat to landscape plants as the Japanese beetle.  When lots of Japanese beetles are present, entire trees can have their leaves nibbled into a lace-like skeleton.  In contrast, when the Japanese weevil feeds, it tends to cut notches out of the edges of leaves.  This damage can resemble the feeding of many caterpillar species, and healthy plants should be able to tolerate the feeding.  Reports from other states suggest that this insect unlikely to cause very severe damage.

The invasive two banded Japanese weevil (Pseudocneorhinus bifasciatus). Photo Credit: Michael C. Thomas, Florida Department of Agriculture and Consumer Services, Bugwood.org
The invasive two banded Japanese weevil (Pseudocneorhinus bifasciatus). Photo Credit: Michael C. Thomas, Florida Department of Agriculture and Consumer Services, Bugwood.org

Think you’ve found the Japanese weevil?

If you come across any beetles in Wisconsin feeding on landscape plants that resemble the Japanese weevil, send digital images and/or physical specimens to the UW Insect Diagnostic Lab for confirmation, so we can track this new arrival in the state.

Wisconsin’s Top Insect Trends of 2015 (#5 – #1)

In this post, we’re continuing to count-down 2015’s top insect trends in the state.  This is the final post in a three part series.  Part I (2015’s diagnostic lab statistics) can be found here and Part II (Top Insect Trends Numbers 10-6) can be found here.

5) Pollinators
With all the headlines about bees, it’s not surprising to see pollinators in the top insect stories again in 2015.  Similar to other years in the recent past, honeybees and other pollinators have been facing declines.  Unfortunately, Wisconsin saw some of the highest honeybee losses in the country, with over 60% colony loss during the 2014-2015 period.  Some good news over the past year has been the development and release of pollinator protection plans.  A federal pollinator protection plan was released in May with the goals of reducing honeybee losses, increasing the population of Monarch butterflies, and increasing pollinator habitat.  In addition, a Wisconsin pollinator protection plan was announced in 2015, and was just released in January of 2016.   Due to the recent declines and their importance to agriculture in the state and nation, pollinators will continue to be in the spotlight in the future.

A ground nesting bee (Colletes sp.) near the stump of the former President's Oak on the UW-Madison campus. Photo Credit: PJ Liesch
A ground nesting bee near the stump of the former President’s Oak on the UW-Madison campus. Photo Credit: PJ Liesch

4) Spring caterpillars
An unexpected insect trend in the spring of 2015 was the surprising abundance of a number of caterpillar species feeding on plants in the landscape.  Caterpillar species, such as the humped green fruitworm, speckled green fruitworm, eastern tent caterpillar, forest tent caterpillar, gypsy moth caterpillar, and the euonymous caterpillar are typically present to some extent, although their numbers have been low the past few years.  For a number of potential reasons, these species had a great spring and during a period in May and June, caterpillars made up roughly 30% of the cases coming in to the diagnostic lab.  Weather patterns (i.e., rainy weather) and natural predators/parasites/diseases can have significant impacts on caterpillar populations each year, so it’ll be interesting to see if we’re faced with a plethora of caterpillars again in 2016.  Additional details of this story were featured in a blog post last June.

3) Viburnum Leaf Beetle
In terms of a new emerging pest with the potential to impact a commonly planted landscape shrub, Viburnum Leaf Beetle is near the top of the list.  As of late 2014, we only knew of a single infested viburnum bush in northern Milwaukee County, which raised the question: is the infestation small enough to contain and/or eradicate?  Some ground truthing this past spring identified many new infestations in SE Wisconsin, in many cases miles from the original site.  At the moment, the viburnum leaf beetle seems to be centered around the four county area where Milwaukee, Waukesha, Washington, and Ozaukee counties meet.  While this insect only feeds on viburnums (and related plants like Arrowwood), the damage can be significant.  It may be some time before this pest spreads elsewhere in the state, but if you have viburnum plants in your yard in SE Wisconsin, be weary!  Additional details of this case were featured in a post last June.

VLB Damage
“Skeletonizing” feeding damage from adult viburnum leaf beetles. Photo courtesy of Paul Weston, Cornell University, Bugwood.org

2) Brown Marmorated Stink Bug
Populations of the invasive Brown Marmorated Stink Bug increased dramatically in 2015 and this insect takes the overall #2 spot in this list (up from #8 last year).  This invasive species was first spotted in the state in 2010, and each year a handful of lone adults have been found in Wisconsin.  In the fall of 2015, we had more sightings of BMSB (30+), than in the past 5 years combined! (Spoiler: this trend has continued into early 2016)  At this point, the “hot spots” in the state are: Dane County, the greater Milwaukee area, and the Fox River Valley.  In addition to being an indoor nuisance pest, BMSB can also feed on and damage a wide variety of plants in home gardens, agricultural fields and orchards.  In other places in the country, the first reports of plant damage have typically been noted ~3-5 years after the initial detection of this species.  With that said, 2016 could be the year that BMSB really takes off and starts wreaking havoc for gardeners and agricultural growers alike.  Additional details of this case can be found in this post from last October.

1) Magnolia Scale
While scale insects have already been mentioned in the “sucking insects” section (#9 on the list), one species in particular, the Magnolia scale (Neolecanium cornuparvum), seemed to stand out amongst all other insects in 2015.  This species is often present in low numbers in the state, but the conditions must have been perfect for their populations to explode last year.  During the months of June and July, reports of Magnolia scale were coming in on almost a daily basis.  Being one of the unusual scale insects, Magnolia scale adults look more like a fungus than an insect (note the whitish blobs in the image below).  Not only did this bizarre looking species pummel Magnolia shrubs and trees in many parts of the state, but the honeydew produced by these insects rained down below, attracting ants and yellowjackets and leading to the growth of unsightly black sooty mold.  A number of predators, parasites, and diseases typically keep Magnolia scale in check, but with the extremely high infestations noted last year, it’s likely that we’ll continue to see some Magnolia scale activity into 2016.  If you experienced magnolia scales first hand, there’s a helpful factsheet available here.

Magnolia twig coated with whitish, fuzzy magnolia scale adults.