Category Archives: Invasive Species

Elm Seed Bug: A New Pest to Watch for in Wisconsin

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.

Elm Seed Bug Infographic
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.

2023 Spongy Moth Season Kicks Off in Wisconsin

Spongy moth (Lymantria dispar) season has officially begun here in Wisconsin. Earlier this week (May 3rd), the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) Pest Survey Program reported caterpillars emerging from an egg mass in far southwestern Wisconsin. Based on forecasting models from the USA Plant Phenology Network, we should expect to see caterpillar emergence begin across much of southern Wisconsin over the next week. As things continue to warm up, the pattern will push further north in the state.

Forecasting map from USA National Phenology Network for predicting hatching of Spongy Moth eggs. Source: USA-NPN (www.usanpn.org)

We may be facing a challenging year from this invasive insect. Dry conditions suppressed a beneficial fungal disease (Entomophaga maimaiga) the last two years and allowed spongy moth populations to build up. Along these lines, DATCP reported a 102% increase in male spongy moths caught in trapping surveys last year.  Likewise, the Wisconsin Department of Natural Resources (DNR) Forest Health Team reported a significant uptick in defoliation last year—from 294 acres defoliated in 2021 to over 85,000 acres defoliated in 2022.

At this point in the season, it’s hard to know how much damage will ultimately occur on yard and forest trees in 2023. However, you can get an estimate of potential defoliation in your own yard by counting egg masses.  Each overwintered spongy moth egg mass contains upwards of 1,000 eggs, so a yard with dozens of egg masses could soon face tens of thousands of hungry caterpillars in the near future.

Dozens of spongy moth egg masses on a tree trunk. Photo credit: Karla Salp, Washington State Dept. Agriculture via Bugwood.

Over the next few weeks, we can expect spongy moth caterpillar activity increase. These small caterpillars will cause a trivial amount of damage at first but will gradually become larger, hungrier, and more damaging over time. Keep an eye out for activity in your yard. If you are inundated with caterpillars, consider using sticky barrier bands and burlap barrier bands to trap them as described on the UW-Madison Extension Spongy Moth website.

Looking at the bigger picture, Mother Nature could hold a trump card for our spongy moth situation. If we end up having a rainy spring, damp conditions could encourage the fungal disease Entomophaga maimaiga to kick in and crash spongy moth populations (this halted outbreaks in SE Wisconsin in 2004 and 2010) . However, if we experience another dry season, it could allow spongy moth populations to build further—stay tuned and hope for rain!

Spongy Moth: 2022 Late-Season Update

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. 

Daily temperatures for Madison, WI in earyl/mid May, 2022
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.

Small spongy moth caterpillars. Photo credit: PJ Liesch, UW Insect Diagnostic Lab

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 as Entomophaga 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. 

 

A New Tool To Help Track Invasive Insects in Wisconsin

The United States Department of Agriculture (USDAdeclared April to be Invasive Plant Pest and Disease Awareness Month. To support this effort, the University of Wisconsin Insect Diagnostic Lab recently launched a new Wisconsin invasive insect mapping page to help track invasive insects in the state.

If you’ve followed this blog for a while, you’ll notice that quite a few of my posts focus on invasive insects.  Why?  In part, it’s because these non-native insects tend to be new or emerging issues and a key role of the UW Insect Diagnostic Lab is to help identify and track new and trending insects in the state. In addition, these invasive insects can sometimes cause significant damage or capture our attention for other reasons.  In a typical year, I see 2-3 new non-native insects show up in Wisconsin, which really adds up over time.  For every species that has arrived here, many more are making progress towards the state (e.g., spotted lanternfly). In other cases, non-native insects show up completely out of the blue.

What’s the big deal with non-native insects?
Non-native insects can cause harm in many different ways:
Introducing the new mapping page:

Because of the impacts mentioned above, it’s helpful to track invasive species so we can better understand where they may be having impacts, and also to get the word out about new detections and allow folks to take appropriate action.  To help in this regard, the IDL’s new invasive insect mapping page hosts a series of maps showing the known county-level distributions of a select list of invasive species.

These particular species have been included due to their relatively recent arrival in Wisconsin, and the ability to track them on a county-by-county basis.  Keep in mind that many other non-native insects can be found in the state, but some of these have been around a long time, are now widespread, and tracking on a county-by-county basis is no longer feasible or helpful (e.g., Japanese beetle, European paper wasps, German yellowjackets, European earwigs, and many more).

The maps on this page will be updated when new detections occur, and additional species maps will be added over time.  If you believe that you’ve observed one of the listed insects in a county where it has not been documented or a new invasive insect species, please collect evidence (physical specimens and/or digital images) and contact me to work on officially confirming the detection.  An example entry from the map page can be found below:

Example entry from the new Wisconsin Invasive Insects Mapping page

Spongy moth: an old pest with a new name

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.

Spongy moth caterpillar. Photo credit: PJ Liesch, UW Insect Diagnostic Lab

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.

Looking back at 2021 at the UW Insect Diagnostic Lab

What a year it’s been. Things seemed like they were getting back to normal this past summer, only for the Omicron variant to pop up and say—not so fast. Despite all the ups-and-downs, services have carried on at the UW Insect Diagnostic Lab in one way or another through the second year of the COVID pandemic. Things have changed a bit and these days I’m on campus much more than a year ago. Throughout the pandemic, demand for services at the IDL has remained high with over 2,400 ID requests in 2021.

Early 2021—The UW Insect Diagnostic Lab was still mostly closed to visitors at the time. Campus services were mostly back to normal by the start of the fall semester on campus. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.

Since COVID first popped up, there have been some subtle shifts in lab statistics—an increase in the percentage of samples solely involving digital images (vs physical specimens) and an overall increase in the proportion of cases coming from the public. Considering the pandemic, this makes sense. Over the last two years, campus buildings and the IDL have been closed to visitors at various points, meaning that clients couldn’t drop off samples. In other cases, it might have been tough to make it to a post office or the UPS store to ship a sample in. Likewise, with many folks working from home, it likely led to more time out in yards and gardens, or visiting local parks or hiking trails—and more time to notice insects.

Looking back at the cases from this last year, 2021 was a unique year due to our unusually hot and dry weather conditions in Wisconsin. Based on data from the Wisconsin State Climatology Office, Madison was quite warm and saw an extra ~500 growing degree days in 2021, but was down about 15 inches of precipitation for the year. Some parts of the state were even hotter and/or drier than Madison and most of the state was categorized as either unusually dry or in some stage of drought during the year [US Drought Monitor].

Drought conditions in Wisconsin as of late December, 2021. It’s been an unusually dry year around the state. Map source: Drought Monitor, UNL.

The weather conditions this year led to some shifts in the insects and related arthropods seen at the UW Insect Diagnostic Lab. A pest that had been relatively quiet the last decade, Lymantria dispar (formerly known as the “gypsy moth”), thrived with the dry conditions this past spring. In “rainy” years, a beneficial fungus (Entomophaga maimaiga) can “kick in” to help keep their numbers in check. If 2022 is another dry year, we could be in store for even more problems from this invasive species. Certain mites also thrived this year and I saw a large number of cases of eriophyid mites causing damage to plants ranging from coneflowers to garlic. Springtails weren’t necessarily more abundant (they feed on decaying plant matter and thrive under damp conditions), but I suspect the hot & dry conditions sent them looking for any place darker, damper, and cooler.  This led to lots of reports as they were trying to invade structures.

We’ll likely continue to see the impacts of the 2021 drought for some time.  Plants, including established trees and shrubs, also suffered from the drought and this will likely lead to an increase in reports of “secondary” insect pests in the next few years. Certain insects can be generally “well behaved” and leave healthy plants alone, only to attack stressed and weakened plants.  As an example, cases of the two-lined chestnut borer (a notable pest of oaks) often increase 1-3 years after a drought, and I’m expecting to see more cases in the coming years.

In the realm of medical entomology, it was a good year for ticks both in Wisconsin and other parts of the US. Black flies (Family Simuliidae) had another strong year in many parts of the state, although calls about these were shifted a bit earlier than in previous years (likely due to an “early” spring). If there’s a silver lining to the drought, it’s that mosquito pressure was down in Wisconsin for much of the summer. As we received a bit more rain in the latter half of summer we saw some late season activity, but disease pressure remained low (only three  West Nile Virus cases in Wisconsin, compared to 50+ in a “bad” year). As recreational and work-related travel increased a bit more in 2021 compared to 2020, I did see an uptick in reports of bed bugs.

With the Asian giant hornet garnering attention in the news for the second year in a row, I continued to see lots of reports of cicada killer wasps, pigeon horntails, great golden digger wasps, and other large insects.  Unfortunately, with the sensationalized hype about “murder hornets” (ahem—New York Times…) I had plenty of reports of other large harmless insects that were killed simply because they “looked big and scary” (one particular photo of a tomentose burying beetle comes to mind…).  Overall, the Asian giant hornet story was really pretty quiet this year, with a limited amount of activity in a small part of the Pacific Northwest.  As of December 2021, the Asian giant hornet has not been found in Wisconsin or anywhere close to us.

Insects like the pigeon horntail (Tremex columba) may be large (as far as insects go), but are completely harmless to humans. I saw plenty of cases where members of the public contacted me after killing such insects simply because they looked “big and scary”.  When publishers such as the New York Times use sensationalized language (i.e., “murder hornet”) there are plenty of negative impacts. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.

I had plenty of reports of social wasps (yellowjackets, bald-faced hornets, and paper wasps) as well as bumble bees this year—including three reports of the endangered rusty-patched bumble bee in the same week in early August! We missed the Brood X “cicada craze” here in Wisconsin, but I still had plenty of questions about them from reporters. We will, however, see some periodical cicadas (Brood XIII) in 2024 in southern Wisconsin.

Some other IDL case highlights from 2021 include:
-An explosion of hackberry emperor butterflies in late spring in south central Wisconsin
-More black witch moths than I’ve ever seen before in a single year (over a dozen sightings!)
-First specimens of the invasive Asiatic garden beetle collected in Wisconsin
-An influx of fall armyworms in late summer, and finally
-Unexpected (live) European insect imported in a Jeep

Every year is a bit different here at the UW Insect Diagnostic Lab and 2021 was no exception.  I’ll be curious to see what 2022 has in store for insects in Wisconsin!

—PJ Liesch
Director of the University of Wisconsin Insect Diagnostic Lab

Asiatic Garden Beetles Collected in Wisconsin for the First Time

Serendipity can play a big role in being an entomologist or any kind of naturalist. Sometimes, you’re simply in the right spot at the right time to make an interesting observation or scientific discovery. There’s lots to learn about the natural world around us and plenty of room for discoveries.

Think about birds for a moment. According to the Wisconsin Society for Ornithology, there are 441 species of birds known from the state. Birders can spend an entire lifetime learning about the biology and habits of these species and how to identify them by sight, song, and other features. Now, think about insects. Here in Wisconsin, our best estimate is that we have somewhere in the ballpark of 20,000 insect species in the state (let alone all the other arthropods!). During talks to the public, I often joke that birders have it easy—with so many insects out there, you could have ten lifetimes and still have plenty to learn and discover!

With that said, there’s lots to be discovered in the world of insects. Even though I’ve been collecting and studying these creatures for over 15 years, I still make discoveries on a regular basis. This often requires hours of diligent observations and the ability to focus on the tiniest of details, but in other cases it comes down to plain old luck. For example, I’ve written about discovering and collecting specimens of the rare fly, Asteia baeta, in my house after setting up a Christmas tree (no such luck this year…).

Photo of adult Asiatic garden beetles
Asiatic garden beetle adults. Photo credit: Emmy Engasser, Wichita State University, Bugwood.org.

A more recent example of entomological serendipity occurred this last July in my own backyard in Dane County. I was enjoying a cold beer on our back deck one warm evening  when I noticed a few small scarab beetles on our window screens. Since I keep a lookout for invasive species as part of my job at the UW Insect Diagnostic Lab, I always have a list of species in mind that I’m keeping an eye out for. In this particular case, the beetles piqued my interest due to their resemblance to the non-native Asiatic garden beetle (Maladera formosae), although we have native species in the genus Serica that can look similar to the naked eye. Just a few weeks before this, I had identified some specimens of the Asiatic garden beetle from a suburb of Chicago, which placed the species on my immediate radar.

Hold my beer, I’m getting some vials. I collected all the specimens I could spot (4), and was able to confirm their identity as the Asiatic garden beetle after tracking down appropriate keys and dissecting out the male genitalia—a surprisingly common and delicate entomological task used to distinguish certain insects that look similar. While I’ve seen a possible report of the AGB on iNaturalist, the specimens from my back deck marked the first specimens of the Asiatic garden beetle collected and confirmed from the state of Wisconsin.

Adult Asiatic garden beetles colleted in Wisconsin.
A few of the Asiatic garden beetle specimens known from Wisconsin. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.

The Asiatic garden beetle first showed up in the United States in New Jersey in the early 1900’s and has spread westward ever since. This species is a notable pest and feeds on a wide range of plants. The adult beetles are “sneaky”—hiding by day and causing most of their damage after dark. They are primarily active on warm evenings (>70˚F) and can be strongly attracted to lights. In this case, not only was I enjoying a cold beer on a warm summer night, but the string of patio lights over our deck likely attracted the beetles from the nearby area. The larvae (white grubs) can be pests of turfgrass, home gardens, and agricultural crops such as corn and potatoes.

Adult Asiatic garden beetle and plant damage.
An adult Asiatic garden beetle and feeding damage on a landscape plant. Photo credit: Whitney Cranshaw, Colorado State University, Bugwood.org.

At this point, I have many more questions than answers about the Asiatic garden beetle and what the future holds for this species in Wisconsin. To date, only a handful of specimens have been collected (four in July and another specimen in mid-September) and no plant damage has been observed. However, I’ll be keeping a close eye on this species, since reports from nearby states suggest that we may be seeing more of this species and damage in the coming years.

Spotted Lanternfly: The Next Big Pest in Wisconsin?

Is the invasive spotted lanternfly (Lycorma delicatula) poised to be a problem in Wisconsin? Only time will tell, but the threat is definitely real.

Spotted lanternfly adult
Adult spotted lanternfly. Photo credit: Emelie Swackhamer, Penn State University, Bugwood.org

What is the spotted lanternfly?
If you haven’t heard of the spotted lanternfly (SLF) before, it may be because this insect hasn’t been spotted in the upper Midwest yet. This invasive planthopper is native southeast Asia and was first spotted in the US (eastern Pennsylvania) in 2014. It has since spread to nearby states in the eastern part of the country. This plant-feeding pest poses significant concerns for both agricultural producers and the general public.

What do spotted lanternflies look like?
Spotted lanternfly adults and juveniles have a unique appearance and can easily be distinguished from our native insects. Adults are roughly 1 inch long with grey and black spotted forewings and bright pink patches on the hindwings; their abdomen is black and yellow. Although they have wings, adults are generally weak fliers and tend to walk or hop. The wingless juveniles (nymphs) are smaller than adults and are mostly black with white spots. When nearly mature, juveniles are red and black with white spots.

In contrast to the conspicuous adults and juveniles, the eggs have a subdued appearance. The small, brownish, seed-like eggs are laid in batches of 30-50 and are covered with a grayish putty-like material. These egg masses can resemble dried mud.

 

What is the life cycle of the spotted lanternfly?
The spotted lanternfly has one generation per year. In late summer, SLF females deposit egg masses containing 30-50 seed-like eggs on trees or other objects. After making it through the winter, the eggs hatch in late spring and juveniles emerge. Juveniles can’t fly, but can walk or hop on plants. The juveniles feed and grow over the course of two months before transforming to adults in mid-summer. Adults are present into the fall as they feed, mate, and lay eggs.

What do spotted lanternflies feed on?
Spotted lanternfies are plant feeders. Their preferred host plant is the invasive tree-of-heaven (Ailanthus altissima), which occurs in its native range in China. However, this pest is known to feed on over 100 different plants. Certain agricultural crops can be attacked, including: hops, pome fruit (apples, pears, etc.), stone fruit (peaches, plums, cherries, etc.), nut trees, grapes, and others. The spotted lanternfly can also feed on a wide range of landscape and forest trees and shrubs which can pose concerns for plant nurseries, homeowners, landscapers, and tree care professionals. Tree and shrub species known to be attacked include: maples, oaks, hickories, walnuts, cherries, catalpa, willows, serviceberry, roses, lilacs, and many others. Spotted lanternflies can feed gregariously and hundreds or thousands of individuals are sometimes spotted on tree trunks or branches.

What type of damage to they cause?
When SLFs feed, they use needle-like mouthparts to pierce plant structures to drink sap. Not only does this wound plants and create potential entry points for disease pathogens, but wounds may continue to ooze for some time—creating an unsightly mess. Significant feeding could cause dieback of branches of trees or shrubs and reduce yields of agricultural crops. The presence of SLF adults at the time of harvest could also pose a potential contamination concern for certain crops. In addition, spotted lanternflies excrete honeydew (undigested sugars) in their waste, which can lead to the growth of black sooty mold on the trunk or base of trees.

Aggregation of spotted lanternfly adults and damage at base of tree
Aggregation of spotted lanternfly adults, oozing feeding wounds, and growth of black sooty mold at base of a tree. Photo credit: Emelie Swackhamer, Penn State University, Bugwood.org

What’s the invasion risk from spotted lanternfly?
There’s significant concern about the spread of the spotted lanternfly. Since the first detection in Pennsylvania in 2014, this insect has already spread to many other states in the eastern US. Overall, spotted lanternflies mostly walk or hop (adults are weak fliers), but they are good at “hitchhiking” which may contribute to their spread; eggs are of particular concern. Egg masses are often laid on plant materials (e.g. tree trunks), but they can also be laid on man-made objects such as pallets, crates, automobiles, trailers, and other items. With their subtle appearance, egg masses can easily be overlooked and could be transported long distances. The movement of eggs could end up playing an important role in the spread of this insect over time.

A 2019 study evaluated potential spotted lanternfly habitat in the United States. The Midwest (including parts of Wisconsin) is expected to be good habitat for this invasive insect, highlighting the importance of early detection of this pest. If you suspect you’ve found the spotted lanternfly in Wisconsin: please take pictures, save any specimens you find, and contact me at the UW Insect Diagnostic Lab.


For additional information about the spotted lanternfly, check out these resources from the UW-Madison Division of Extension and the Wisconsin Department of Agriculture, Trade and Consumer Protection.

Hindsight: 2020 Trends at the Wisconsin Insect Diagnostic Lab

When the COVID situation reared its head back in March of 2020, I wasn’t sure how it would impact activities at the UW Insect Diagnostic Lab.  While there was a shift to handling diagnostics mostly remotely, in the end, 2020’s caseload of 2,533 ID requests was just shy of 2019’s all-time record of 2,542 cases.  

With Governor Evers’ Stay-at-Home Order last spring, our attentions were occupied by the unraveling pandemic and caseload at the UW Insect Diagnostic Lab was lighter than usual around that time.  However, as Wisconsinites shifted to working from home, it meant spending more time in yards and many Wisconsinites pulled out their green thumbs and established COVID “Victory Gardens”.  As a result, the diagnostic lab saw a record number of cases in July of 2020, with close to 600 ID requests that month alone. 

Monthly caseload at the UW Insect Diagnostic Lab in 2020. Credit: PJ Liesch, UW-Entomology.

Outreach activities of the lab saw a dramatic shift as well.  With in-person presentations and workshops off the table, virtual events afforded new opportunities—like a Japanese beetle seminar in July which drew nearly 900 participants. Regular events, like my appearances on WPR’s The Larry Meiller Show also continued through 2020, although I fielded calls from my home’s “reading nook” rather than the WPR studio.  

One of the biggest insect stories of 2020 was the Asian giant hornet.  Last May we learned that Asian giant hornets had survived the winter in the Pacific Northwest.  This of course led to a distinct increase of so-called “sightings” of that insect in Wisconsin, although every  “sighting” ended up being common insects from our area.  Last year, I saw dozens of ID requests for insects which ended up being look-alikes such as cicada killer wasps, pigeon horntails, and great golden digger wasps.  To date, the nearest sighting of the Asian giant hornet is well over 1,000 miles from us here in Wisconsin and poses no immediate threat to the upper Midwest.  Further reading: 6 Things to Know about the Asian Giant Hornet.

Some invasive pests had big years as well.  The viburnum leaf beetle, lily leaf beetle, purple carrot seed moth, and brown marmorated stink bug all increased their footholds in the state. Japanese beetle numbers varied a lot depending on where you were located in Wisconsin.  Some areas saw little pressure during droughty periods, while other parts of Wisconsin saw high Japanese beetle activity.  Gypsy moths had been quiet in Wisconsin for several years, but increased their numbers last year.  I saw a distinct increase of gypsy moth cases in 2020, and I’ll be keeping a close eye on that species in 2021.   

Come fall, we saw some stretches of unseasonably pleasant temperatures in October, November, and December.  During those periods, multicolored Asian lady beetles—which had been lurking in the background for several years—returned to the spotlight.  The multicolored Asian lady beetle activity around Wisconsin was some of the highest of the last decade.  Not to be left out of the fun, minute pirate bugs were abundant in some parts of the state and made warm, sunny fall days a little less pleasant due to their biting habits.  Speaking of biting insects, black flies were abundant in 2020 and made outdoor activities more challenging in June and July.  Mosquito activity varied around the state, although we did see a few cases of the Eastern Equine Encephalitis in 2020.

While we won’t see a big emergence of 17-year periodical cicadas in Wisconsin until 2024, small numbers of out-of-sync “stragglers” did emerge in southeastern Wisconsin last summer. 

A female Dryinid wasp. The forelegs are highly modified into scythe-like claws used to grasp other insects. Photo credit: Ty Londo.

No two years are the same at the UW Insect Diagnostic Lab and that includes some of the “X-Files” type cases as well.  Some of my favorite cases from 2020 include identifying phorid flies from dead radioactive cats (it’s a long story…), a grim-reaper-esque dryinid wasp, several massive black-witch moths from Central America, and a case involving a black widow spider found in a head of broccoli from the grocery store.  Never a dull moment at the UW Insect Diagnostic Lab!

—PJ Liesch
Director, UW Insect Diagnostic Lab

6 Things to Know About The Asian Giant Hornet

Asian giant hornets have hit the news recently, sometimes going by the name of “murder hornets”.  Below are six key things to know about these insects and the situation in North America:


1) What is the Asian Giant Hornet?
The Asian giant hornet (Vespa mandarinia), which is also known as the “great sparrow bee” in its native range (or recently sensationalized as the “murder hornet”) is a wasp species native to parts of southern and eastern Asia. The Asian giant hornet is amongst the world’s largest wasps, with queens approaching a length of 2 inches (typically ~1.5 inches). Workers and males are smaller, but still measure over an inch long. Asian giant hornets have a distinctive appearance with a bright yellowish-orange head, a dark body, and alternating dark and yellowish stripes on the gaster (“abdomen”). This species creates subterranean nests, which commonly have a peak workforce of around 100 workers.

A distinctive Asian giant hornet adult. Photo Credit: Washington State Dept. Agriculture, Bugwood.org

Asian giant hornets pose threats as an invasive species in North America. These insects are efficient predators with complex hunting behaviors. While Asian giant hornets prey upon a wide range of insects, they are capable of attacking honey bees. Under the right conditions, Asian giant hornets can decimate hives of European honey bees (Apis mellifera) within a few hours.  Their potent stings can also pose medical concerns for humans.


2) What’s the risk in the Midwest?
Based on the current situation, the risk from Asian giant hornets in Wisconsin and the Midwestern US is extremely low. To date, Asian giant hornets have never been found in Wisconsin or surrounding states. A very small number of Asian giant hornets were spotted in southwestern British Columbia and northwestern Washington state in the second half of 2019. For Wisconsin, these sightings have been roughly 1,500 miles from us. At the time this article was written (early May 2020), Asian giant hornets had not been spotted in North America in 2020. Update 5/27/20: we recently learned that AGHs have made it through the winter in North America.  This species recently resurfaced, as reported in the New York TimesDespite this recent finding, all confirmed sightings of the AGH are from the Pacific Northwest and these insects pose little risk for the Midwest at this time. Update 12/20: No substantial changes by the end of 2020—in North America, AGHs are still only known from far northwestern Washington State and nearby parts of British Columbia.  This insect has not been documented anywhere outside of that range. 


3) What’s the timeline of the Asian giant hornet story?
Asian giant hornets have gotten a lot of attention in the news recently, but these stories really missed the main “action”, which occurred roughly half a year ago. (Imagine if Sport Illustrated took half a year to write about the Super Bowl’s winning team!). The story of the Asian giant hornet in North America began in August of 2019 when a beekeeper in Nanaimo, British Columbia (SE Vancouver Island) spotted these wasps. Three specimens were collected at the time and their identity was confirmed.

Also in August of 2019, a beekeeper in Northern Bellingham, Washington (US) observed Asian giant hornets, but no specimens were collected. Back in Nanaimo, British Columbia, an Asian giant hornet nest was located and eradicated in an urban park (Robin’s Park) in September. A month later (late October, 2019) a specimen was photographed in nearby mainland British Columbia (White Rock, BC). Around that time, the same beekeeper in Northern Bellingham, Washington observed Asian giant hornets attacking a hive. The last sighting of the Asian giant hornet occurred near Blaine, Washington in December of 2019, when a dead specimen was collected and a live specimen was spotted at a hummingbird feeder.

Update June, 2020: Small numbers of AGHs have been reported in North America—but only in the pacific Northwest. 


4) Have Asian giant hornets become established in North America?
The ability of the Asian giant hornet to survive and spread in North America is not understood at this time. In its native range, the Asian giant hornet is associated with forested and low mountainous areas with temperate or subtropical climates.  A key unanswered question at the moment is: have the Asian giant hornets successfully overwintered in North America? Update 5/27: we recently learned that AGHs have made it through the winter.  This species recently resurfaced, as reported in the New York Times.

Asian giant hornets overwinter as queens.  If previously fertilized, queens attempt to establish nests during the spring months. Established nests won’t produce the next batch of queens to carry on their “blood lines” until mid-fall, meaning that responders monitoring the situation in the Pacific northwest will have roughly half a year to hunt down any nests. For this reason, 2020 will be a critical “make or break” year in the story of the Asian giant hornet in North America.

Responders in the Pacific Northwest have plans to monitor for Asian giant hornets with traps and visual methods. If spotted, individual hornets can potentially be tracked back to their nest to allow responders to eradicate the colonies. Full details of the USDA response plan can be viewed here.


5) Health risks to humans are low
By referring to the Asian giant hornet as “murder hornets”, recent news stories have given the false impression that these insects pose a regular threat to humans. Many stories have repeated the claim that Asian giant hornets kill around 50 people a year in Japan, where these hornets naturally occur. In reality, the actual numbers are much lower. Based on publicly available data from the Japanese e-Stat statistics portal, from 2009-2018 an average of 18 deaths were reported annually in Japan from hornets, wasps, and bees combined. For comparative purposes, roughly twice as many annual deaths (average of 35) were reported as the result of slipping and drowning in bathtubs over that same period of time.

Annual Deaths in Japan due to hornets, wasps and bees. Data source: Japan e-State website (https://www.e-stat.go.jp/en)

Nonetheless, Asian giant hornets do have potent venom and 1/4 inch-long stingers, which pack a punch.  Due to their large physical size, a relatively large volume of venom can be injected leading to painful stings. If many stings occur (such as if one were to disrupt a nest), medical attention is advised.


6) Are there any look-alikes?
While we don’t have Asian giant hornets in Wisconsin or the Midwest, we have plenty of other insects that are currently being mistaken for the Asian giant hornet or could be mistaken for these hornets later this year. Panicked individuals thinking they’ve found an Asian giant hornet might end up killing native, beneficial insects which pose little risk to humans—such as bumble bee queens, which are currently trying to establish their nests for the year.

Historically, the UW Insect Diagnostic Lab receives many suspected reports of Asian giant hornets every year—all of these have been misidentifications by the submitters. To date, no confirmed sightings of the Asian giant hornet have occurred in Wisconsin or the Midwestern US. However, with the media spotlight on the Asian giant hornet, an increase in false reports is expected at the UW Insect Diagnostic Lab this year.  Click the diagram below to view a full-size version.

Asian giant hornets and common look-alikes of the Midwest. Diagram organized by PJ Liesch, UW Insect Diagnostic Lab. Click for larger version.

Some of the commonest look-alikes include:

Cicada Killer Wasps (Sphecius speciosus) These are the closest match in terms of size. However, these solitary ground-nesting wasps are really quite harmless, unless you happen to be a cicada... Because these insects don’t have a colony to defend, they are very unlikely to sting.  This is the top look-alike reported to the UW Insect Diagnostic Lab every year. For additional details see this post: Asian Giant Hornets—Nope!

Great Golden Digger Wasps (Sphex ichneumoneus) These solitary ground nesting wasps capture and feed katydids and related insects to their young.  Because these insects don’t have a colony to defend, they tend to be docile.

Pigeon Horntails (Tremex columba) These primitive wasp-like insects develop inside of decaying trees as larvae and can be common.  They are not capable of stinging, but females do possess a prominent egg-laying structure (ovipositor).

Elm Sawflies (Cimbex americana) These plump, wasp-like insects cannot sting. The caterpillar-like larvae can feed on elms, willows, birches, and other hardwood trees.

Bumble Bees (Bombus spp.) The Midwest is home to over 20 species of bumble bees. These beneficial pollinators play important roles in the ecosystem. Bumble bees do live together as colonies and can act defensively if the nest is directly disturbed, but these important pollinators are generally docile. Annual colonies reach maximum size in late summer and naturally die out in the fall.

Yellowjackets (Vespula spp. & Dolichovespula spp.) The Midwest is home to more than 10 species of yellowjackets. Common species, such as the German yellowjacket (Vespula germanica) are typically around ½ inch in length. Yellowjackets are social insects and depending on the species, nests can occur in the ground, in hollow voids (such as soffit overhangs or wall voids), or as exposed as papier-mâché type aerial nests. Annual colonies reach maximum size in late summer and die out naturally in the fall.

Bald-Faced Hornets (Dolichovespula maculata) Our largest social wasp in the Midwestern US, reaching lengths of approximately ¾ inch. Bald-faced hornets are technically a type of “yellowjacket” but have a distinctive black and white appearance. These insects create large papier-mâché type nests, which can approach the size of a basketball. Annual colonies reach maximum size in late summer and die out in the fall.