Category Archives: Outdoor Insect Invaders

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?

Wisconsin’s Top Insect Trends of 2016 (#5 – #1)

In this post, we’re continuing to count-down 2016’s top insect trends in the state.  This is the final post in a three part series.  Part I (2016’s diagnostic lab statistics) can be found here and Part II (Top Insect Trends Numbers 10-6) can be found here.

#5: The spread of the emerald ash borer increased dramatically in the state last year. Photo Credit: Howard Russell, Bugwood.org.
#4: Fall invading insects, such as boxelder bugs are well known, but the strawberry root weevil and other weevils can sneak indoors during the summer months. Photo Credit: Whitney Cranshaw, Bugwood.org.
#3: Several scarab beetles, including the rose chafer caused notable plant damage last year. Photo Credit: Clemson University Extension, Bugwood.org.
#2: An elusive adult rabbit bot fly. Photo Credit: Quentin Sprengelmeyer.
#2: An inch long bot fly larva from a mouse. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab.
#1: Fierce mosquito pressure in many parts of the state combined with the Zika stories in the news gave mosquitoes the top spot in 2016's insect trends. Photo credit: Susan Ellis, Bugwood.org.

 

5) Metallic Wood Boring Beetles
Two different metallic wood boring beetles (Family Buprestidae) had strong years in 2016. The first, the emerald ash borer, is no stranger to Wisconsinites these past few years. While there were only 3 new counties (Portage, Wood, Sawyer) added to the state quarantine map in 2016, there were over 80 municipalities with their first confirmed EAB infestation last year (out of 227 municipalities with documented EAB finds at the end of 2016). With that said, EAB has greatly picked up steam these past few years and is attacking ash trees at a rapid rate in Midwest.

Another metallic wood borer that seemed to have a good year was the twolined chestnut borer. Unlike the invasive emerald ash borer, the twolined chestnut borer is is native to North America and tends to attack stressed trees (oaks). In these cases, trees might be stressed by factors such as disease, drought stress, winter injury, or damage from other insects. The UW Insect Diagnostic Lab noticed a distinct increase in cases of the twolined chestnut borer this past summer, although the underlying stress might have begun affecting trees several years ago. With the high value of oak trees in the landscape, this insect is definitely a pest that tree care companies should have on their radar for the near future.

4) Home-Invading Weevils
Many Wisconsinites experience or at least are familiar with insects that sneak indoors in the fall, such as boxelder bugs and multicolored Asian lady beetles. There’s also a group of broad-nosed weevils that happen to sneak indoors during the summer months. Species in this group include the strawberry root weevil, the imported longhorned weevil, and others. Once indoors, these weevils tend to stumble around in a slow, somewhat tick-like manner, causing concern to homeowners. But fear no weevil, for these insects are completely harmless. A broom or vacuum cleaner are often the best tools to deal with them. While broad nosed weevils can be somewhat common, reports coming in to the UW Insect Diagnostic Lab suggest that numbers of these home-invading beetles were up in 2016.

3) Scarab Beetles
A number of scarab beetles had noteworthy activity in 2016, including several important landscape pests. Scarab beetles can be an extremely common group of insects, with well over 100 species in Wisconsin alone. Perhaps the best known (and most infamous) member of this group would be the Japanese beetle (Popillia japonica), which seemed to rebound last year after a few quiet years. In parts of the state with sandy soil, the rose chafer was present in high and damaging numbers. Similar to Japanese beetles, rose chafers are fond of feeding on a wide range of plants from landscape shrubs to fruit trees.

Two other scarab beetles were noteworthy in 2016: the Northern masked chafer and the European chafer. This past year marked the first year that the larvae of these beetles (white grubs) had been found damaging turfgrass in the state: Rock County (NMC) and Door county (EC). Previously, turfgrass managers only had to contend with the white grubs of Japanese beetle and the occasional May/June beetle.

2) Bot Flies
[Disclaimer: bot flies are not for the faint of heart! If you’re preparing to eat lunch, you may want to skip down to #1.]
Bot Flies-Click to Read

If you’re not familiar with bot flies, these creatures may seem like something out of a science fiction movie. In their simplest terms, bot fly larvae are essentially large, flesh-inhabiting maggots. When fully mature, the maggots can be over an inch long and are covered with tiny backward-facing spines, making removal nearly impossible from their host. Adult bot flies are very short lived and somewhat resemble bumble bees or certain horse flies in their size and coloration. In a typical year, the UW Insect Diagnostic Lab might receive 1-2 reports. For whatever reason, bot flies had a great year in 2016 and several dozen reports came in to the lab. The common species observed in Wisconsin last year were from the genus Cuterebra and parasitize small mammals such as: mice, chipmunks, squirrels, and rabbits.  The maggots live and feed beneath the skin of their mammal host for weeks before popping out to pupate.  The mammal hosts generally seem to tolerate their companions, although the concept of bot flies may give you a creepy-crawly feeling.
[Bonus material: there is a bot fly (Dermatobia hominis) in South and Central America that affects humans]

 

1) Mosquitoes
With all the stories about the Zika virus in the news, it was difficult to avoid hearing about mosquitoes in 2016. In addition, with the heavy rains many parts of Wisconsin received last year, it was equally challenging to venture outdoors and avoid mosquitoes. In many parts of the state, mosquito pressure was severe last year, giving mosquitoes the top spot on the 2016 list. If there’s a silver lining to the mosquito story last year, it has three parts:

  • The mosquitoes that were dreadfully abundant last year (floodwater mosquitoes) aren’t important vectors of human disease. Yes, they might have ruined that evening cookout, but at least they weren’t making anyone ill.
  • Reports of mosquito-borne diseases (such as West Nile Virus) were relatively low in the state last year.
  • Zika virus was not a major issue in Wisconsin, as the mosquito species responsible for that disease haven’t been found here [Read more about this topic in this post]

Conifer Seed Bugs

Since last week’s press release on the Brown Marmorated Stink Bug by the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) and my own blog post on this invasive pest, I’ve been getting many reports of this insect from Wisconsin residents.  It’s always great to get reports from the community as it helps us keep track of this invasive pest.

Brown Marmorated Stink Bug ID
Identifying features of the Brown Marmorated Stink Bug; click for larger version. Photo Credit: PJ Liesch, UW-Entomology

Interestingly, there have also been many cases of an insect that somewhat resembles BMSB: the Western Conifer Seed Bug.  Both insects try sneaking into buildings to look for shelter and possess “checkerboard” patterns at the back of the body.  However, when you have the insects side by side, they can be easily separated.  The western conifer seed bug is longer and more slender in appearance, has dull reddish and orange patches on the body, and has distinctly dilated hind legs (think “bell-bottoms”).  In addition, these insects possess a unique zig-zag (“lightning bolt”) pattern on each wing, which can easily be seen with the naked eye as illustrated in the ID guide below.

Western Conifer Seed Bug-ID Guide_opt
Distinguishing features of the Brown Marmorated Stink Bug and Western Conifer Seed Bug; click for larger version. Photo Credit: PJ Liesch, UW-Entomology

While the western conifer seed bug  can sneak into buildings in the fall, they tend to invade in relatively low numbers.  This species feeds on the seed cones of pines and other conifers, but doesn’t seem to cause much (if any) harm to the trees.  Overall, they can be a bit of a nuisance, but that’s about it, unlike BMSB, which can potentially damage many different types of plants.

Have western conifer seed bugs around the house and want to know more about their biology and management?  Check out this handy factsheet from UW-Extension.

Why Such a Stink About a Bug?

Every fall, residents throughout Wisconsin and many other parts of the country face an invasion by a number of insects: boxelder bugs, multicolored Asian lady beetles, western conifer seed bugs and cluster flies, to name a few.  With the coming frosts, these insects are simply trying to find a sheltered location to settle for the winter.  Out in nature, many of these insects would simply crawl into a rock pile or beneath the loose bark of a dead tree to overwinter.

MALB Overwintering_opt
Multicolored Asian Lady Beetles often spend the winter in sheltered spots, such as beneath the bark of dead trees. However, they can just as easily sneak into buildings. Photo Credit: PJ Liesch, UW-Entomology

But why rough it out in nature if there are perfectly good buildings to sneak in to?  Next time you’re cleaning the gutters, take a moment to peek around the outside of your house.  Small gaps in siding, soffit areas, around door and window frames, and cracks in the foundation are all potential spots for insects to sneak through.  And if they make it through?  Well, you could be in for some extended visitors. . .

In addition to the usual fall invaders, a relative newcomer starting to pop up in Wisconsin and other parts of the Midwest is the invasive Brown Marmorated Stink Bug (Halyomorpha halys).  Like the boxelder bugs and multicolored Asian lady beetles, brown marmorated stink bugs (BMSB) like to find their way indoors for the winter.  This Asian species was first detected in Wisconsin back in 2010 and for reasons we don’t fully understand, their numbers have been quite low the past few years.  As of late 2014, BMSB has been confirmed or suspected in 10 Wisconsin counties, with most of the reports coming out of the Madison and Milwaukee area.  A handful of sightings each year has been the pattern.

Unfortunately, we may be at the beginning of a shift in BMSB populations in the state.  In early 2015, there were at least 6 specimens found in Wisconsin by early March.  Despite the quiet summer, the sightings have started popping up again in late September and October of this year.  What’s more concerning is that we’re starting to see groups of these insects clustered together (previous sightings had consisted almost exclusively of lone individuals).

Not only are these unwanted houseguests a nuisance, but quite frankly, they smell bad.  True to their title of “stink bug”, brown marmorated stink bugs possess glands that can emit a pungent odor.  Some consider the odor to be coriander-like, while others  say it resembles musty gym socks.  Invasive species [check].  Nuisance invader [check].  Smells bad [check].  That’s all, right?  Unfortunately, not quite.  Just like a bad late-night infomercial: Wait! There’s more!

Bad Bug Checklist-Upload

It turns out that brown marmorated stink bug has the potential to be quite a nasty plant pest and rivals the Japanese beetle in the breadth of its palate.  Brown marmorated stink bug seems to feed on just about anything under the sun: field crops like corn and soybeans, vegetables like tomatoes and peppers, and even ornamental trees and shrubsFruits like apples and grapes can be hit especially hard.  In some cases, the mere presence of BMSB can be a problem: imagine being a vintner and having your batch of wine tainted by the presence of a few squished stink bugs!  In the eastern U.S. there are regular reports of agricultural problems and growers have to spray to control these insects.  We haven’t had any reports of plant damage in Wisconsin yet, but that could change over time if BMSB populations continue to climb.

So what can you do about brown marmorated stink bugs?  For starters, learning to tell them apart from our native stink bugs is relatively easy.  Look for the alternating “checkerboard” pattern along the back edge of these half-inch long insects and the two light bands on the otherwise brown antennae.

Brown Marmorated Stink Bug ID
Identifying features of the Brown Marmorated Stink Bug; click for larger version. Photo Credit: PJ Liesch, UW-Entomology

With relatively few sightings in Wisconsin at this point, we’re still trying to get a feel for where this insect is.  If you suspect that there may be brown marmorated stink bugs around your house, take a picture of the insect and email it to me at (pliesch@wisc.edu) for identification.  Another option is to collect a physical sample and mail them in to the Insect Diagnostic Lab for identification (instructions on how to submit samples can be found here).

If brown marmorated stink bugs or other fall invading insects are trying to get into your house, one of the best things to do is to inspect the outside of your home and physically seal up cracks and crevices where they’re trying to sneak in.  Once fall invaders are indoors, hauling out the hose attachment on the vacuum cleaner is often one of the best steps to remove them.

 

Hedgehogs of the Microscopic World

The case load is generally pretty quiet around the UW-Madison Insect Diagnostic Lab during the first few months of the year. There are still the cases of conifer seed bugs or multicolored Asian lady beetles which are the norm for January, February and March. Occasionally I get some interesting specimens (like the cedar tree borer) which emerge from firewood that had been brought in and stored next to the fireplace. My most interesting case lately has been a sample which I was convinced contained small, hairy carpet beetle larvae. I placed the specimen under the microscope to confirm my suspicions, only to be surprised to find that it had a lot more than six legs. With that one glance, the mundane had become the bizarre.  I vaguely recognized the creatures I was staring at through the microscope, as I must have seen them in a book once before.

A few minutes of digging and I had my ID: an unusual type of millipede called a “duff millipede” or “dwarf millipede” from the genus Polyxenus. At only a millimeter or two long, these millipedes are hardly noticeable unless they’re moving against a light colored background. Typically, when I hear of millipedes, I think of the slow-moving, dark-colored, creatures that curl up when disturbed and are frequently associated with moisture and decaying organic matter. When it comes to duff millipedes, you have to take most of your preconceptions about millipedes and throw them out the window. Not only are they incredibly small, but their armature of spines makes them resemble a miniature hedgehog (cuteness, included) or some kind of character from the Muppets.

Polyxenidae
A “duff millipede” (Polyxenus species). Photo Credit: PJ Liesch

So what do these little spine-balls do anyways? If you dug into the literature, you’d find that they’re often associated with tree bark, leaf litter, or old stone walls and are thought to feed on algae. Other than that, there isn’t much known about them—except for their fascinating defensive mechanisms. Most millipedes rely on chemical defenses to keep predators at bay (including the ability to secrete cyanide).  Some polyxenids take a very different approach and use a physical defense consisting of detachable, barbed spines reminiscent of those novelty “finger trap” toys from childhood. Thomas Eisner and colleagues found that these detachable spines can get hooked on the bodies of would-be predators (such as ants), allowing the millipede to escape while the hungry predator attempts to extricate itself. Like the “finger trap” toys, the more the predator struggles to free itself, the more entangled the barbs become. In some cases, the predators can even die from this entanglement.  [You can read a detailed description of this defensive mechanism here: http://www.pnas.org/content/93/20/10848.full.pdf]

Entanglement by microscopic millipedes: what a way to go. . .

Wisconsin’s Top 10 Insect Stories of 2014 (Part II)

Below you’ll find the second part of a three part series describing the Top 10 insect-related stories of 2014 from Wisconsin. Part three will be released next week.


7) Missing Pests: As every landscaper and farmer knows, there’s a certain batch of insect pests that tend to pop up consistently each year. One of the biggest stories of 2014 was the scarcity of some of these “regulars” like the gypsy moth and the Japanese beetle. The reason behind this? We likely have Mother Nature to thank. Gypsy moth populations fare poorly during periods of wet weather due to the proliferation of a fungal disease that kills the caterpillars. We certainly had abundant and consistent rainfall in 2014, and several images of diseased insects made their way into the lab. In addition, gypsy moth numbers have been in a general decline for several years in the state, which is good news for oak trees.

If there’s one good thing that came out of the brutally cold winter of 2013-14, there’s the fact that it may have helped knock down the Japanese beetle populations. Japanese beetles overwinter as white grubs in the soil and tend to move just deep enough to avoid the frost line. With the pipe-bursting cold and deep frosts of last winter, it seems that the deep freeze knocked their numbers down. As a result, reports of damage from Japanese beetles were scarce this past summer. While it’s too early to tell, it’s possible that it may only be a one-year reprieve. Turfgrass researchers have reported decent grub numbers in turfgrass areas this fall, which could mean that Japanese beetle numbers could creep back up in the future.

A female Japanese beetle digging into the turf to lay her eggs. Photo Credit: PJ Liesch.
A female Japanese beetle digging into the turf to lay her eggs.
Photo Credit: PJ Liesch.

Agricultural pests were also down in 2014, with no major pest outbreaks. Two of our best known corn pests, the European corn borer and corn rootworms, had very slow years. Even migratory crop pests, such as the potato leafhopper and black cutworm, which overwinter in the gulf coasts states and migrate northward in the spring failed to take off in 2014.  (A full summary of agricultural pests can be found here.)

6) Interesting “Structural Pest” Trends: Two of our insects that commonly invade homes in the fall (boxelder bugs and multi-colored Asian lady beetles) had drastically different trends this year. Box elder bugs thrive under dry conditions, like we had in the latter parts of 2012 and 2013. Similar to the gypsy moth mentioned above, the damp conditions in 2014 likely helped keep the box elder bug number in check and prevented the widespread numbers that we’ve seen the past few years.   While the numbers of box elder bugs were low this fall, the multicolored Asian lady beetle, which had been low for the past few years, started popping up in decent numbers in certain parts of the state. One warm October day, I wandered out to the front of the entomology department building on campus to view thousands of the lady beetles flying around looking for overwintering spots.

5) Invasion of the Copper Underwing: Most folks have never heard of a moth called the copper underwing. Rightly so, as it tends to be a fairly obscure species. The caterpillars are commonly called the green humped fruitworms and can feed on fruit trees and other trees. When adults rest on trees, their grayish appearance isn’t much to write home about. However, when they display their hind wings, you’d notice the brilliant copper color and understand the common name of the insect.

Copper Underwing
Copper Underwing (Amphipyra pyramidoides); Photo credit PJ Liesch

For whatever reason, 2014 seemed to be perfect for this species. Perhaps I should have suspected that the few adults I spotted at my porch lights in late spring were the beginning of a trend. As the summer went on, I started getting reports of large numbers of these moths congregating on the sides of homes, sneaking under siding, and even leaving excrement stains on siding. All in all, I had reports of “home invasions” from over a dozen counties, mostly in the southwestern part of the state. Because this species tends to be present in low numbers, I suspect that we won’t see them amassing by the thousands again anytime soon.

Part 3: Coming soon