Ask the Experts: A Monthly Garden and Landscape Q&A Series Sponsored by the UW-Madison Division of Extension Horticulture Program
Join our monthly online programs in 2024 for an opportunity to connect with plant health experts from the UW-Madison Division of Extension. Each session, held on Monday afternoons from 1:00-2:00 PM, is your chance to ask questions about your trees and shrubs, garden vegetables and ornamentals, lawns and more. Whether it’s about plant diseases, insects, or the selection and general care of plants in and around your home, our panel of seasoned experts will provide you with insightful answers. Don’t miss out on this opportunity to cultivate your knowledge and keep your plants thriving.
These online sessions are free but registration is required for each one that you would like to attend (see links below). Upon registration you will receive an email confirmation with the link for joining the session. All sessions are Mondays from 1:00-2:00 PM.
January 22, 2024 To register for this session, click here.
February 19, 2024 To register for this session, click here.
March 18, 2024 To register for this session, click here.
April 22, 2024 To register for this session, click here.
May 20, 2024 To register for this session, click here.
June 17, 2024 To register for this session, click here.
July 22, 2024 To register for this session, click here.
August 19, 2024 To register for this session, click here.
September 23, 2024 To register for this session, click here.
October 21, 2024 To register for this session, click here.
November 18, 2024 To register for this session, click here.
December 16, 2024 To register for this session, click here.
Note: As of late 2023, elm seed bug (ESB) has not yet been found in Wisconsin, but could show up in our area in the near future.
The elm seed bug (Arocatus melanocephalus| Hemiptera: Lygaeidae) is an invasive insect species native to parts of Europe. It was first detected in North America in 2012 in western Idaho and is now established in western parts of the continental US and Canada. In the eastern US, we haven’t seen much of this insect yet. It was technically spotted in the general Detroit area in Michigan in 2015 and reports continue to pop up in southeastern Michigan. This last summer, I helped confirm the presence of the elm seed bug (and the Asiatic garden beetle!) in the Twin Cities area for the Minnesota Department of Agriculture. Given the proximity to the Wisconsin state line, the elm seed bug could make an appearance in our state in the not-too-distant future.
Overall, elm seed bugs have habits similar to boxelder bugs and birch catkin bugs in that they feed on trees outdoors before invading structures later in the year. True to its common name, the elm seed bug is associated with elm trees and is especially fond of feeding on the seeds. They have little overall impact on the health of the trees. Later in the year, adult elm seed bugs seek out sheltered overwintering spots. In natural settings, they would typically overwinter beneath loose bark of trees or similar locations. However, they can readily invade homes and other structures in large numbers. Indoors, elm seed bugs are harmless to humans, but can be a general nuisance. Like brown marmorated stink bugs, elm seed bugs can also produce an unpleasant odor when crushed. Because ESBs are a nuisance invader like boxelder bugs and multicolored Asian lady beetles, management is going to be very similar and should focus mostly preventing these insects from getting indoors, e.g., physical exclusion and exterior crack and crevice treatments.
Infographic describing the main features of the elm seed bug (Arocatus melanocephalus). Infographic created by PJ Liesch, UW Insect Diagnostic Lab. Click for larger version.
Since we have not yet seen elm seed bugs in Wisconsin, having this insect on our radar and being able to recognize it are the most important things at the moment. Elm seed bugs are similar in body shape to boxelder bugs, but are slightly smaller at roughly ¼ – ⅓ inch long. The adults are a dark brownish-black color with rusty-colored patches behind the head. There is a blackish, triangular structure (scutellum) on the middle of the back which sits within a rusty-colored, square-shaped patch. The edge of the abdomen is marked with a series of small, pale spots and the underside of the abdomen is a rusty, reddish color as well.
Wisconsin residents believing that they’ve found elm seed bugs are encouraged to collect a sample and contact me at the UW Insect Diagnostic Lab to definitively confirm the identity of the specimens: insectlab.russell.wisc.edu.
Heading into the growing season, spongy moth (Lymantria dispar, formerly known as the “gypsy moth”) was poised to have a big year in Wisconsin.That prediction has held up and I’ve seen an influx of reports of spongy moth caterpillars and damage at the UW Insect Diagnostic Lab (IDL) this spring.In some areas, these caterpillars are causing conspicuous damage, which has also led to a flurry of questions from the public on what to do about them.Let’s take a look at how this season has shaped up, how the next few weeks could turn out, and what can be done.
What’s happened so far (as of mid-June)?
After a cool start to spring, we saw some unseasonably warm temperatures during the second week of May, which jump-started a lot of insect activity.I saw a distinct increase in diagnostic requests at the IDL around this time as well as my first reports of spongy moth caterpillars.
Unseasonably warm temperatures (90+˚F) for Madison, WI in early/mid May kicked off a lot of insect activity. Source: Weather Underground.
Initial sightings of small caterpillars mostly involved larvae dangling from trees and structures from silken threads—a dispersal mechanism down as “ballooning”.In other cases, thousands of tiny, dark caterpillars stood out against light-colored siding of homes. At first, these tiny caterpillars couldn’t cause much damage—with their small size, they simply don’t eat much.It isn’t until caterpillars are larger and more mature that they really start to chow down and damage increases dramatically. It’s estimated that 80-90% of the damage caused by these caterpillars is from the final two larval substages (instars). Reports of notable damage started to pop up a few weeks later in early June.
Based on the reports coming in to the UW Insect Diagnostic Lab, the heaviest spongy moth activity in 2022 spans from southeastern Wisconsin (Lake Geneva area) west through Rock, Green, and Dane Counties, and north to Sauk, Juneau and Monroe Counties.Overall, Dane and Walworth Counties stand out for the number of spongy moth sightings and reports of damage that I’ve received.
What will the next few weeks be like?
The end of caterpillar activity is in sight—but we’re not there yet.I’m still getting reports of spongy moth caterpillars and likely will for a few more weeks.In many cases, the caterpillars being spotted are now pretty large (1¾– 2 inches), meaning that they’re feeding voraciously and causing lots of damage to plants. If there’s a silver lining, it’s that these large caterpillars should also be pupating in the near future—putting an end to their damage for the season. However, I’ve been receiving reports of mixed caterpillar sizes, with some caterpillars only measuring ¾ – 1 inch long.These smaller “stragglers” will continue to feed and cause damage into July, meaning we’re not entirely out of the woods yet.
A large spongy moth caterpillar showing the distinctive color pattern (click for larger view). The larger, more mature caterpillars cause the bulk of the feeding damage. Photo credit: PJ Liesch, UW Insect Diagnostic Lab
Another variable that could be at play this year is a beneficial fungus known asEntomophaga maimaiga.This disease can specifically infect and kill spongy moth caterpillars and can play an important role in regulating their populations over time.Last year’s drought likely helped set the stage for 2022 by suppressing this beneficial fungus. This spring we’ve had pretty regular precipitation in many parts of the Midwest, which could help put a dent in spongy moth populations if this pathogen kicks in.
What can be done about spongy moth?
This has been one of the commonest questions I’ve been getting recently and have seen plenty of posts on social media sites like Facebook and Nextdoor asking this same question. Management of spongy moth really depends on the life stage of the insect. The UW-Madison Division of Extension Spongy Moth website has an excellent month-by-month discussion of management approaches.
For small numbers of yard trees, the burlap band method can be a way to remove larger caterpillars from the equation.However, it’s important to understand that this method can be time and labor intensive as you need to check bands daily and brush caterpillars into a container of soapy water to maximize effectiveness. [Note: don’t touch the caterpillars bare-handed, it hurts!].For large trees, there’s not much else that an individual homeowner can do other than discussing chemical treatment options with an arborist. Many of the online posts I’ve seen have had an element of panic, but it’s also important to keep in mind that trees that are in otherwise good health can generally tolerate defoliation and will push out another batch of leaves later this year.I start to worry more about plant health when trees are defoliated repeatedly, as that can lead to secondary issues over time.
Burlap band around an oak tree. Large spongy moth caterpillars feed mostly at night, so burlap bands offer a convenient daytime hiding spot. Caterpillars can then be brushed into a container of soapy water. Photo credit: Bill McNee, WI-DNR.
I’ve also seen a number of questions about aerial sprays for spongy moth.This year, the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) has been coordinating aerial spraying in the western parts of the state to slow the overall spread of this invasive species.The treatment used in early-season aerial sprays (Bacillus thuringiensis kurstaki) is most effective against small caterpillars. Later spraying will focus on disrupting the ability of adult moths to successfully find a mate. In theory, members of the public could band together to coordinate aerial spraying in their local area, but the planning process for this can take months.By the time folks were posting on social media expressing a desire for aerial treatments in their neighborhood, that option was no longer feasible.
One key thing to pay attention to later this summer will be the egg masses laid by adult female spongy moths. Each egg mass can contain upwards of 1,000 eggs, so surveying for egg masses can give insight into what the spongy moth situation could be like in 2023. Those egg masses will also remain in place for roughly nine months until they hatch next spring, which gives lots of time for a search-and-destroy scavenger hunt in your yard.
For additional information on managing spongy moths, check out the updated UW-Madison Division of Extension factsheet on this insect and the Extension spongy moth website with month-by-month recommendations.
The spongy moth, Lymantria dispar has recently been in the news because of its new name. If you haven’t heard of the “spongy moth” before, it’s probably because you learned of this insect as the “gypsy moth”. It’s the same exact creature, just with a new common name.
Why the change?The word “gypsy” in this insect’s name was originally a reference to persons of Romani descent—“the popular name of the gypsy was no doubt suggested by the brown, tanned kind of color of the male” [Forbush & Fernald, 1896]. In 2021, the Entomological Society of America’s Better Common Names Project started to review the common names used to communicate about insects. Common names that include derogatory or inappropriate terms are being assessed. After a lengthy review process, the term “spongy moth” was ultimately decided upon to describe Lymantria dispar—and fittingly so. The beige egg masses of this insect have a soft, spongy consistency. In French-speaking parts of its range, this species has long been known as La Spongieuse for this very reason. Thus, you’ll be hearing more about the “spongy moth” over time as the term “gypsy moth” is phased out from educational/government websites and other resources.
In addition to the name change, the spongy moth should be on our radar for other reasons. Despite being in Wisconsin for decades, this pest can still be a serious defoliator of hardwood trees, both in yards and forested areas. From the period of 2014 – 2020, spongy moths haven’t been much of an issue. An important reason for this is a beneficial fungus known as Entomophaga maimaiga. This fungus was introduced from Japan and it is strongly associated with the spongy moth. Although it took some time to make an impact in the US, this fungus is now viewed as an important “check” on spongy moth populations. Spring rains encourage this fungus, which can cause high mortality amongst spongy moth caterpillars. However, in many parts of Wisconsin we saw an unusually dry year in 2021 which likely curbed the impacts of this fungus. As a result, I saw an increase in cases and reports of spongy moth caterpillars and their damage, adults, and egg masses at the UW Insect Diagnostic Lab last year and Wisconsin also saw a subtle uptick in defoliation of forested areas.
Defoliation (acreage) due to the spongy moth in Wisconsin over time. Source: Wisconsin DNR Forest Health 2021 Annual Report
As illustrated in the chart above, spongy moth populations can be very dynamic and can explode under the right conditions—leading to extensive defoliation. The egg-laying strategy of this species plays an important role in this dynamic. Adult female spongy moths deposit egg masses that can easily contain upwards of 1,000 eggs. In late summer and fall of 2021, I saw plenty of reports where trees contained dozens of egg masses, which could turn into tens of thousands of hungry caterpillars this spring.
Adult female spongy moth depositing eggs. The spongy beige egg mass can easily contain 1,000 or more eggs. Photo credit: Ryan Hodnett via Wikipedia.
Luckily, there’s still a bit of time to take advantage of this knowledge as the young caterpillars typically don’t become active until late April or early May. In the meantime, removal or destruction of the egg masses could help reduce local populations. While often found on trees, the egg masses can also be located on just about any surface in a yard—stacked boards, sides of structures, piles of firewood, and even on vehicles. Don’t delay if you noticed spongy moth activity in your area last year, since it won’t be long before the caterpillars are out and active this spring.
Reference: Forbush, E. H. and C.H. Fernald. 1896. The gypsy moth. Porthetria dispar A report of the work of destroying the insect in the commonwealth of Massachusetts, together with an account of its history and habits both in Massachusetts and Europe. Boston, Wright & Potter. 495pp.
Will we see Brood X cicadas in Wisconsin or the upper Midwest this year? Read on to find out: Cicadas—they’re all over the news and soon to be out by the billions. All this buzz is about periodical cicadas, a group of species from the genus Magicicada which emerge once every 17 years (or every 13 years in some cases). Periodical cicadas are only found in the eastern United States and vary by location and the timing of their activity. To help categorize these insects, entomologists refer to each cohort of cicadas as a “brood” and have numbered them with Roman numerals. This year’s cicadas are referred to as Brood X (i.e., Brood ten) and last emerged in 2004.
Brood XIII periodical cicadas in Lake Forest, IL in June of 2007. Photo Credit: Janet and Phil via Flickr (CC).
Periodical cicadas are amongst the longest lived insects and their long life span and massive emergences are believed to be a survival strategy—by overwhelming predators with sheer numbers, they simply can’t all be eaten. But the wait for their appearance is a long one. Periodical cicadas spend 17 years below ground as juveniles (nymphs) feeding on the sap from tree roots, before making their way above ground. Their emergence is associated with soil temperatures, and when the soil has warmed to 64˚F, they emerge. This corresponds to parts of April, May, or June depending on the location on the map. Once they make their way above ground, the cicadas molt and transform into adults. Shortly thereafter, a raucous mating free-for-all commences. After mating, the females cut small slits into twigs of trees to deposit their eggs. The eggs hatch and the juveniles head to the soil for their lengthy development. Periodical cicadas don’t live long as adults (a matter of weeks), so it’s a long build up to a noisy grand finale.
Ground covered by periodical cicadas. When these insects emerge, it can be by the billions! Photo credit: James St. John, via Wikipedia (CC).
With all the attention in the news, many Wisconsinites and other Midwesterners are wondering if they’ll be able to see or hear Brood X cicadas in their area this year. For Wisconsin, Minnesota, Iowa, and most of Michigan and Illinois the answer is no—although they aren’t terribly far away either. Brood X cicadas can be found in over a dozen eastern states, but primarily emerge in three main pockets:
Indiana, Ohio and nearby slivers of eastern Illinois and southern Michigan
Southern Pennsylvania and parts of nearby Delaware, Maryland, Virginia, New Jersey, and New York
Eastern Tennessee and nearby parts of North Carolina and Georgia
Map of active periodical cicada broods of the United States. Map credit: USDA Forest Service. Click map for full size version and additional information.
While we won’t see Brood X cicadas here in Wisconsin, we will see other periodical cicadas in the not so distant future. Wisconsin is home to Brood XIII cicadas, which last emerged in 2007, meaning that the next big emergence in the Badger State is only a few years off in 2024. In the meantime, we’ll still see and hear plenty of our typical “dog day” cicadas during the warm days of summer. To learn more about Brood XIII cicadas in Wisconsin, check out this post from last year.
When it comes to insects that bite humans, there’s simply not a very long list of “common suspects”—especially during the cooler months. Things such as bed bugs, fleas, and lice are all fairly straightforward to confirm. However, I do occasionally bump into other creatures that can bite, such as bird mites, pirate bugs, and others. I also bump into cases where clients are experiencing biting or crawling sensations, but no insects of concern are found. One of my tasks at the UW Insect Diagnostic Lab is to evaluate a situation to see if any of the less-common possibilities might be at play. If not, then I start to suspect delusory parasitosis (aka Ekbom’s Syndrome), which entomologists encounter on a fairly regular basis. In one recent case, I was scratching my head for a while until I was able to confirm the presence of hackberry psyllids (Pachypsylla spp.)—tiny, jumping, biting insects that pop up under the right conditions.
A hackberry psyllid (Pachypsylla sp.). Several species in this genus cause galls on the leaves of hackberry trees. Photo credit: Katja Schulz, via Flick.
Hackberry psyllids (pronounced “sill-ids”) resemble miniature cicadas and are about 1/10th inch long. They have mottled grayish bodies and are sometimes called “jumping plant lice” or “hackberry nipple gall makers”. True to their name, these insects are associated with hackberry trees (Celtis occidentalis), which are commonly planted in the landscape as both yard and street trees.
In spring, overwintered psyllids lay eggs on emerging hackberry leaves. After the young psyllids emerge, their feeding causes unusual distortion of the leaf tissue, resulting in small “nipple-like” lumps (galls) on the leaves. Such galls are actually very common and most hackberry trees possess the characteristic galls to some extent. They may be alarming in appearance, but the galls are harmless to the trees and are essentially a minor “cosmetic” issue. The young psyllids feed and develop within the protection of their leaf galls. Eventually, they complete their development and the next generation of adult psyllids emerges from the galls.
Galls on the underside of a hackberry leaf caused by psyllids from the genus Pachypsylla. Photo credit: Beatriz Moisset via Wikipedia
At this point, you might be wondering how these tiny plant-feeding insects end up bugging humans. Similar to boxelder bugs and Asian lady beetles, hackberry psyllids seek out sheltered overwintering spots in the fall and can easily invade homes and other structures. With their tiny size, hackberry psyllids can be a bit harder to keep outdoors. They are often overlooked and can easily squeeze through most window screens. Indoors, these insects face death by desiccation due to the dry conditions, but can be a nuisance as they jump or fly around. Occasionally, they’ll invade in fall and their activity resumes during warm spells over the course of a winter.
In addition to being a nuisance, hackberry psyllids can “bite”. These insects feed on plants (hackberry trees), but they do have a habit of “testing” various surfaces they land on to assess if another food source has been found. If they happen to land on exposed skin, they’ll use their slender, beak-like mouthparts to probe, which can feel like a small pinch. When they do this, hackberry psyllids don’t feed on blood or inject any kind of venom, but it certainly can be unpleasant.
The good news is that unless you have a hackberry tree in your yard or very close by, you probably won’t bump into appreciable numbers of these tiny insects. If you do encounter them at your home, leaving windows closed on warm fall days (especially on south and west-facing sides of your house) or replacing window screens with a finer sized mesh can go a long way towards keeping them outside.
In the grand scheme of things, most insects (and spiders) are loners. Perhaps they set a good example for us in 2020 with their social distancing.
Of course, insects have to find a mate to reproduce at some point in their lives*, but out of the 1 million+ described insect species, being truly “social” isn’t the norm. There certainly are some well-known examples of insects that are eusocial—i.e., they live together as a colony. Examples include ants, certain types of wasps (such as yellowjackets and paper wasps), some bees, termites, and a few other interesting examples. However, there are many insects that are much more solitary in their habits. If you think of our bees in the Great Lakes region, we have roughly 500 species. Other than honey bees, bumble bees and a few others, the vast majority of these species are solitary creatures with each female doing her own thing.
Two herds of Cerastipsocus venosus barklice. Photo submitted to UW Insect Diagnostic Lab.
Interestingly, there’s a quirky insect that can be commonly encountered this time of the year and it missed the memo on social distancing. I’m referring to an interesting species of barklouse (Order Psocodea): Cerastipsocus venosus. Barklice are relatives of true lice (e.g., head lice and pubic lice) but they’re really quite harmless to humans and tend to be scavengers. Barklice make up an obscure group of insects and many entomology students simply identify them to “order” level as this group can be challenging to narrow down further to family, genus, or species.
Group of Cerastipsocus venosus juveniles. Note the striped abdomens which make them easy to identify. Photo submitted to UW Insect Diagnostic Lab.iny
If you haven’t encountered Cerastipsocus venosus (aka “tree cattle”) before, it might catch you off guard to find a group (formally known as a “herd”) of these small insects hanging out together on the bark of a tree or a rock in your yard. The tiny juveniles are particularly striking with yellow stripes on their abdomens. The adults are larger (up to 1/4″ long) and possess black wings.
A Cerastipsocus venosus adult. Note the black wings, which are only found in the adults. Photo submitted to UW Insect Diagnostic Lab.
Rest assured, these barklice pose no threat to trees or other plants in our yard and these native insects simply nibble on lichens, and pieces of dead tree bark. Every year I get many reports of these insects in mid- and late- summer at the UW Insect Diagnostic Lab and there’s no need to spray or do anything about these if you spot them in your yard. These barklice don’t seem to stay in the same place for very long, so perhaps their herds just move along looking for greener pastures.
*Some insects are able to reproduce asexually, and don’t technically have to find a mate…
A heavy infestation of elongate hemlock scales. Heavy infestations can have significant impacts on conifers. Photo Credit: Eric R. Day, Virginia Polytechnic Institute and State University, Bugwood.org.
Elongate hemlock scale attacks over 40 species of conifers—especially hemlocks which can be common throughout the Appalachian Mountains, and Fraser firs and balsam firs, which are commonly grown as Christmas trees. Certain types of spruces and pines can also be attacked. Established populations of elongate hemlock scale are not known from Wisconsin, but a recent detection of this pest in the state raises concerns for Christmas tree growers, the plant nursery industry, tree care professionals, and homeowners with conifer trees in their yards. Forested areas are also at risk, meaning the stakes are potentially high with this insect.
While insect activity is quiet in the Midwest this time of the year, we’re hearing about the elongate hemlock scale now due to its Christmas connection. Similar to 2018, the Wisconsin Department of Agriculture, Trade and Consumer Protection recently found that fir Christmas trees, wreaths, and other holiday decorations infested with EHS had been shipped to Wisconsin from North Carolina. The picturesque Blue Ridge Mountains of western North Carolina provide ideal habitat for Fraser firs—one of the most popular species of Christmas trees. North Carolina grows approximately a quarter of all the Christmas trees sold in the US each year and with elongate hemlock scale established in that state, it increases the risk of movement of this invasive insect around the country.
The Blue Ridge Mountains near the border of North Carolina and Tennessee—the native habitat of Fraser firs. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab.
Elongate hemlock scales look unusual as far as insects go. These insects have traded mobility for defense—they hunker down on plants and produce a waxy coating which helps protect them from predators and parasites. As a result, elongate hemlock scales aren’t easily recognizable as insects since the usual signs of segmentation—body regions, legs, antennae—are not readily visible. Instead, these insects have a vague, oblong appearance. Adult females are small (just under 1/10th of an inch long) and are covered with a waxy brownish coating. They are typically found on the undersides of needles. Males are slightly smaller and develop beneath pale whitish coverings. Mature males do emerge with wings but are weak fliers and travel short distances to mate with the wingless, immobile females.
Two adult female elongate hemlock sales on the underside of a fir needle. Females are approximately 2 mm long. Photo Credit: Lorraine Graney, Bartlett Tree Experts, Bugwood.org
Under their protective coatings, these insects use needle-like mouthparts to suck fluids from plants. With their small size, damage occurs when large numbers of individuals infest plants. Their waxy coverings also limit the effectiveness of insecticides, making EHS a challenging pest to control if they become established.
Because elongate hemlock scale has been detected in Wisconsin this year in Christmas trees and other holiday decorations, a key objective at this point is to prevent this insect from getting a foothold in the state. By all means, continue to enjoy your holiday decorations, but when you’re ready to remove these materials, take the following steps to help prevent this insect from becoming established in Wisconsin:
1) If your Christmas tree or natural wreaths, garlands, or other decorations are from a local Christmas tree farm or elsewhere in Wisconsin, no special precautions are needed for elongate hemlock scale. Because EHS is not established in the state, these materials can be removed as usual at the end of the holiday season.
2) If your Christmas tree or natural wreaths, garlands, or other decorations are from a big box store, grocery store, or similar vendor, or if you are not sure of the origins of these materials, it is advised to check these materials for signs of elongate hemlock scale (i.e., brown spots on the undersides of needles). The Wisconsin Department of Agriculture, Trade, and Consumer Protection is advising that infested or suspect materials preferably be burned (check with the DNR for any burning restrictions in your area). Alternatively, such materials could be bagged and discarded as waste. Infested or suspect materials should not be composted or used for wildlife habitat in your yard.
For additional information on elongate hemlock scale, visit the WI-DATCP EHS page and the recent press release about the 2019 EHS detection.
Author’s Note: Original post updated in January, 2019 due to a confirmed report in Waupaca Co. and suspected report in Oneida Co.
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, 28 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 eight new counties in 2018 alone—Eau Claire, Jackson, La Crosse, Marquette, Monroe, Richland, Trempealeau, and Waupaca counties.
Distribution of the brown marmorated stink bug in Wisconsin—updated January 4th, 2019. BMSB has been confirmed in 28 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.
Keep and eye out for BMSB in your area—reports to the UW Insect Diagnostic Lab are encouraged from counties where BMSB is relatively new or has not yet been found (see map above)
Like a kid watching a summer thunderstorm slowly rolling in and wondering how long until the rumbles would be directly overhead, I’ve had a morbid fascination with watching the progression of the emerald ash borer in the Midwest for over a decade. Although emerald ash borer wasn’t found in Wisconsin until 2008, my connection with EAB precedes that by a few years. It turns out my first job as a budding entomologist was as a summer intern for UW-Extension looking for signs of the insect in the state during the summers of 2005 and 2006. Fast forward twelve years and that storm is finally overhead, at least in my neck of the woods. I knew such a time would come, but it really hits close to home when the sounds of chainsaws mark the final days of your neighborhood’s ash trees—at least the ones that aren’t being treated.
EAB Detection and Quarantines as of May 19, 2017. Click for larger version. Image source: WI-DATCP.
At the time of writing, 42 counties in Wisconsin have been quarantined for EAB. While the southeastern part of the state has already been hit hard (green on the map above), a large chunk of the state has not yet seen the emerald ash borer or has only seen light pressure (click the map above to see more details on this topic). Unfortunately, this means that the emerald storm will only be getting worse over the coming years. Along these lines, when EAB first arrived in Wisconsin, spread was slow and the annual number of new community-level detections was small. However, as the populations of this insect have built up in the state, the number of new detections has increased dramatically as illustrated below:
Chart created using data from WI-DATCP on May 22, 2017. Click for a larger version.
Unfortunately, the outlook for the Midwest’s ash trees doesn’t look good and we’ll still be dealing with this insect for years to come. Ironically, this isn’t the first time that we’ve watched a scenario like this play out. As the baby boomer generation grew up, they watched as elms were devastated by the likes of Dutch elm disease. As with emerald ash borer, Dutch elm disease had significant impacts on forested and urban areas and led to irreversible changes in the landscape around us.
With all this Doom-and-Gloom, is there a light at the end of the tunnel? Possibly—but it may be a ways off. For the time being, there are insecticide treatments available that can maintain the health of ash trees, although treatments are costly and are only feasible for relatively small numbers of trees. Biological control is being explored as a potential way to control EAB populations, although results have been limited thus far. However, with any biological control program, it can take years to work the kinks out of the system and see results.
A long-term plan may be to develop varieties of ash trees that are resistant to attack by the emerald ash borer. In several locations in Ohio and Michigan, scientists have found a small percentage of “lingering” ash trees that have survived the initial onslaught of EAB and are monitoring those trees over time for continued survival and genetic traits that may help stave off infestations. Interestingly, one particular species of ash (blue ash, Fraxinus quadrangulata) may hold important clues for long-term ash survival. In some spots in Michigan, >60% of blue ash trees have survived in areas attacked by emerald ash borer. While tree breeding programs may ultimately develop a resistant ash variety, this is likely years away and for the time being we’ll have to face the emerald storm.
Larval tunnels of the emerald ash borer beneath the bark of an ash tree. This damage disrupts the flow of water and nutrients and ultimately kills the tree. Image source: PJ Liesch, UW Entomology.
