Tag Archives: In the News

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. 

 

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.

Fall Armyworms: A Late Summer Surprise in Wisconsin

It’s been hard to miss the recent news headlines about fall armyworms “FAW” (Spodoptera frugiperda). States east of the Rockies have seen historical outbreaks of this insect in 2021, including a bit of fall armyworm activity here in Wisconsin. In some cases, the caterpillars have decimated entire crop fields or home lawns overnight before marching onwards in search of “greener pastures”.

We usually don’t see much of the fall armyworm in Wisconsin and it’s primarily a pest of warmer areas, such as the gulf coast states.  The FAW is native to tropical and subtropical parts of the western hemisphere and the larvae (caterpillars) can feed on dozens of different types of plants—ranging from field crops to fruits and vegetables and even turfgrass. They can be particularly important pests to crops such as corn, grains, and alfalfa.

Fall armyworm caterpillar
Fall armyworm caterpillar. Photo credit: Frank Peairs, Colorado State University, Bugwood.org.

The fall armyworm can’t survive the winters in the US, other than the southernmost areas (e.g., southern Texas and Florida). However, in spring and summer the adult moths migrate northwards and lay eggs. Over the course of many generations and subsequent northward migration, fall armyworms can make it to the upper Midwest and even parts of southern Canada. Historically, fall armyworm has rarely been a notable pest in Wisconsin or the upper Midwest—it simply arrives too late or in too small of numbers to be a concern. To a certain extent, every year is a roll of the dice, but the odds are usually in our favor in Wisconsin and other northern states.

Fall armyworm adult moth
Fall armyworm adult moth. Photo credit: Lyle Buss, University of Florida, Bugwood.org.

This year has been different though, with large numbers being spotted northwards and reports of significant damage coming in from nearby states such as Illinois, Indiana, Iowa, and Ohio. Many other states ranging from Kansas to the mid-Atlantic region have also been impacted in the later parts of summer. While there have been scattered reports of fall armyworm damage to field crops in southern parts of Wisconsin, the lateness of this pest’s arrival and our declining temperatures have likely spared us from the widespread damage seen in other states.

Under hot conditions (e.g. temps in the 90’s), the life cycle of the fall armyworm—from eggs to adult moths—can take only a few weeks. However, fall armyworms are “cold blooded” creatures and cooler temperatures slow down their growth and development. Depending on how chilly it is, their life cycle can be “stretched out” to take 60 days or longer—leaving them much more vulnerable to predation, parasitism, or exposure to frosts.

Eggs of the fall armyworm
Fall armyworm eggs from a residential yard. Photo submitted to UW Insect Diagnostic Lab in September, 2021.

One study* found that fall armyworm eggs didn’t hatch at all if temperatures were cool enough (though not particularly chilly by Wisconsin standards). That particular study simulated daytime/nighttime temperatures of 21˚C (70˚F) and 8˚C (46˚F)—temperatures that are “in the ballpark” for many parts of Wisconsin by mid-September and are often considered downright “pleasant” by Wisconsinites.  Eggs held at warmer temperatures in the experiment hatched just fine.

For eggs that did hatch this year in Wisconsin, cool temperatures also could have helped us out by slowing down their development. As they grow, fall armyworms pass through six sub-stages (instars). The early instar caterpillars are so small, they simply can’t eat much and cause little damage. It’s not until FAW caterpillars become more mature fifth and sixth instars that they really start to chow down and cause significant damage to plants. Thus, falling temps could help prevent the fall armyworm caterpillars from making it to the destructive late instar stages and could also leave them more exposed to a variety of threats.

Chart showing quantity eaten by fall armyworm larval instars.
Graphic representation of the amount eaten by fall armyworm caterpillars in an early USDA experiment. Early instar caterpillars eat little compared to late instars. Cool temperatures limiting their development could help prevent damage by the FAW. Credit: USDA Technical Bulletin No. 34

The fall armyworm outbreak of 2021 could very well be a “once every few decades” type of event, and our northern location likely helped us avoid the significant problems seen in other states. However, if changing climate gives the fall armyworm a “head start” by overwintering farther north, it’s possible that we could see more of this pest in Wisconsin in the future.


*Barfield, Mitchell, and Poe. 1987. A Temperature-Dependent Model for Fall Armyworm Development.  Annals of the Entomological Society of America. 71(1): 70-74.

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.

Brood X Cicadas in the Midwest?

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.

Two periodical cicadas on a rock
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
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 noalthough 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:

  1. Indiana, Ohio and nearby slivers of eastern Illinois and southern Michigan
  2. Southern Pennsylvania and parts of nearby Delaware, Maryland, Virginia, New Jersey, and New York
  3. Eastern Tennessee and nearby parts of North Carolina and Georgia
Periodical Cicada Brood Map from US Forest Service
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.

The Monarch’s Precarious Position

Endangered. It’s an imposing term and not one to be taken lightly. Monarchs have been in a perilous spot for years and there have been rumblings of potentially listing monarch butterflies (Danaus plexippus) as endangered by the US Fish & Wildlife Service. After delays, we finally received a decision in December of 2020—“warranted but precluded”.

Monarch butterfly on the UW-Madison Campus. Photo Credit: PJ Liesch, UW Entomology.

In a technical sense, labeling a species as endangered isn’t as simple as merely placing it on a list. There’s a lengthy review process and potential species are evaluated in terms of how pressing their situation is. In the case of monarchs, the “warranted” part of the decision indicates that monarchs are indeed in need of protection. The alarming part is the “but precluded” statement—it essentially means that other species are facing even more pressing situations and are ahead in line. Some consider us to be in the midst of the “sixth” major extinction event on planet earth, although this one differs in that it’s caused by humans. In short, there are a lot of species that will be facing declines and extinction. At the time of the monarch’s decision from US FWS, there were currently 161 other species listed ahead of monarchs in the priority queue.

Unfortunately, since the US FWS decision last December, we’ve had some alarming news come out about monarch populations. First, it’s helpful to understand monarchs in the US as we actually have two main populations: a western population and an eastern population.

The western population can be found in states such as California, Oregon, Washington, Idaho, Nevada, and Utah west of the Rocky Mountains (a natural barrier to dispersal). While we may think of monarchs migrating to the area outside of Mexico City, this western population heads from their summer grounds to overwinter in parts of southern California. Unfortunately in January of 2021, the Xerces Society reported that only 1,914 total overwintering monarch butterflies were counted—a 99.9% decrease over the last 30 years. For comparison, a similar assessment conducted  in 1997 estimated over 1.2 million overwintering monarchs. Experts have estimated a critical “extinction threshold” of 30,000 monarchs for this western population to hang on. With fewer than 2,000 monarchs spotted in late 2020, the western monarch’s situation can’t get any more urgent.

In the Midwest, we see the eastern monarch population which ranges over much of eastern North America east of the Rocky Mountains. These are the monarchs that make the long perilous flight to overwinter in the mountains outside of Mexico City. While the eastern monarch population’s situation isn’t necessarily as dire as out west, it’s still tenuous to say the least. An assessment of the eastern population is usually released in late winter and the most recent estimate found a 26% drop in overwintering monarch populations compared to last year. Over the last 20 years, the eastern monarch population has declined by approximately 90%. With larger numbers of butterflies in the eastern population, scientists don’t count individual butterflies to gauge their numbers. Instead they estimate the area occupied by densely-packed overwintering monarchs clustered together by the thousands on pine trees at their overwintering habitat in Mexico. The recent assessment found monarchs packed into an area of 2.1 hectares (5.2 acres). While this may sound like a big area packed to the gills with butterflies, it’s estimated that 6 hectares (14.8 acres) of overwintering monarchs is a “critical mass” needed to maintain the eastern population. Unfortunately, the news of both the eastern and western monarch populations comes as a punch to the gut since their numbers have been trending downwards over time.

Assessment of overwintering monarch butterflies, released 2021. Source: MonarchWatch.  Click for more detail.

While monarchs may be in a tight spot, they aren’t gone yet. With the “warranted but precluded” finding, the US Fish & Wildlife Service now considers monarchs a “candidate” species for listing and will continue to assess the situation as higher priority species are added to the endangered species list. In the meantime, if you’re looking for ways to help monarchs, the Wisconsin Monarch Collaborative was created in 2018 to coordinate conservation efforts of this species in our state—check out their website to see what you can do to help the monarchs: https://wiatri.net/Projects/Monarchs/.

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

Busy beetles: lady beetles take to the air and our homes

The spectacular fall weather this week has made it hard to work indoors. As Midwesterners, we know to appreciate the current warm spell as winter is just around the corner. If you’re like me, you’ve probably made it outside to take care of yard work, hike, grill out, or simply enjoy the fall colors. Speaking of colors, you’ve probably notices flashes of orange on the side of your home—multicolored Asian lady beetles (Harmonia axyridis). This fall, we’re seeing surprisingly high numbers of these lady beetles across Wisconsin.

An adult multicolored Asian lady beetle (Harmonia axyridis). Note the black “W” pattern just behind the head which helps identify this species. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.

Just like us, the final warm days of autumn have worked these lady beetles into a frenzy of outdoor activity and our recent weather patterns are the key to this phenomenon. While not native to North America, the Asian lady beetle is an adaptable species and has a good feel for the seasons—it also knows that winter is coming. An important cue for lady beetle activity is the first frost or period of near-freezing temperatures in fall. This sets the stage and when the temperatures creep back up into the mid-60’s or 70’s, it initiates a massive game of hide-and-seek-shelter for these insects.

A group of overwintering Asian lady beetles beneath the loose bark of a dead tree. Photo credit: PJ Liesch, UW Insect Diagnostic Lab

But why our homes? It turns out that Asian lady beetles don’t necessarily want to invade our homes—they simply look for sheltered spots to spend the winter. In more natural settings, I’ve found dozens of these beetles beneath the loose bark of dead trees or in firewood piles during the winter months.

In their native range of eastern Asia, multicolored Asian lady beetles are cliff dwellers. These beetles use visual cues to actively seek out conspicuous, exposed rock faces with cracks to squeeze into. They’re particularly fond of south or west facing cliffs, which get warmed by the sun in the afternoon when they’re most active. The lady beetles fly to these rock outcrops and examine the cracks and crevices to see if a suitable overwintering site has been found.  To us, our homes don’t necessarily resemble cliffs, but to the Asian lady beetles, the basic formula is there: large contrasting objects that stand out in the landscape with an abundance of vertical and horizontal lines resulting from modern design and construction methods. To the beetles, this looks close enough that they’ll fly to structures and wander around seeking out nooks and crannies to slip into as shown in the video clip below from the UW-Madison campus.

From the lady beetle’s point of view, these insects would really prefer to slip into a sheltered crack or crevice, hunker down for the winter, and leave again in the spring. However, when these insects get beneath siding or into a soffit area of our homes, they can accidentally pop out in the living quarters of the home—much to the dismay of the human inhabitants. This isn’t ideal for the insects either, which can face death by desiccation in the dry winter air indoors.

Enjoy these final warm days of autumn, because we’ll all be bundled up inside soon enough—with or without a bunch of lady beetles.


My final two cents: One of the best, long-term approaches to prevent nuisance issues with multicolored Asian lady beetles and other insects (like boxelder bugs and brown marmorated stink bugs) is to have good physical exclusion. This refers to making sure that potential entrance points on structures are sealed up due to good construction methods, caulk, expanding insulation foam, weatherstripping, or similar means.

Given their small general size, multicolored Asian lady beetles can squeeze through cracks or gaps as small as ⅛ inch in size. For perspective, this is about the same height as two pennies stacked atop one another. With that said, if you can easily slide two stacked pennies into a crack or crevice on the side of your house—it’s a big enough opening for multicolored Asian lady beetles to potentially get in!

 

Cicada Mania in Wisconsin?…Not ‘Til 2024

Perhaps you’ve heard some buzz about periodical cicadas (Magicicada spp.) lately. These insects resemble our typical “dog day” cicadas, which we see in mid-to-late summer in Wisconsin, but they are orange and black with vibrant reddish eyes instead of a dull greenish color. Parts of the US are currently seeing mass emergences of periodical cicadas, which appear by the millions every 13 or 17 years depending on the species. I’ve had a number of questions this last month asking if this was “the year” for us to see them in Wisconsin, but it’s not time for the big show…yet.

Left: A common “dog day” cicada; photo credit: PJ Liesch, UW Insect Diagnostic Lab. Right: A peridoical cicada; photo credit: Jay Sturner, via Wikipedia

Periodical cicadas are sorted into cohorts known as “broods”, which occur in particular geographic areas and emerge at specific points in time. For the most part, these insects are excellent timekeepers and some broods have been documented as far back as the 1600’s in the eastern US. There are entire websites and apps dedicated to these insects and their schedules, and scientists have labelled broods with Roman numerals to help differentiate the cohorts.

Map of active periodical cicada broods of the United States. Map credit: USDA Forest Service. Click map for full size version and additional information.

With all the broods out there, some parts of the US do see these cohorts overlap in space, but these can be separated by the years in which they emerge.  In Wisconsin, the situation is fairly straightforward as we only see a single brood: Brood XIII. Brood XIII’s 17-year cicadas last emerged in 2007, meaning that we’ve got four more years to wait until their mass emergence in 2024.

Interestingly, I’ve received a number of photos and reports of periodical cicadas in Wisconsin over the last month or so. I’ve had several confirmed reports from the Lake Geneva area (Walworth County) a confirmed report from southeastern Dane County, and a suspected report from Sauk County.  While most periodical cicadas stick to the schedule, occasionally some of these insects veer off course. These out-of-sync individuals are referred to as “stragglers” and it turns out that Brood XIII has a history of these stragglers. In the late 1960’s, large numbers of stragglers were documented in the Chicago area. Likewise, many of the Chicago suburbs are seeing a similar phenomenon this year. With that said, we did technically see some periodical cicadas this year, but we’ll have to wait a few more years before the real “fireworks”.

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.