Ask the Experts: A Monthly Garden and Landscape Q&A Series Sponsored by the UW-Madison Division of Extension Horticulture Program
Join our monthly online programs in 2024 for an opportunity to connect with plant health experts from the UW-Madison Division of Extension. Each session, held on Monday afternoons from 1:00-2:00 PM, is your chance to ask questions about your trees and shrubs, garden vegetables and ornamentals, lawns and more. Whether it’s about plant diseases, insects, or the selection and general care of plants in and around your home, our panel of seasoned experts will provide you with insightful answers. Don’t miss out on this opportunity to cultivate your knowledge and keep your plants thriving.
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If you’re seeing insect damage on your roses this spring, you aren’t alone and there are a number of early-season insect that can catch our attention. For example, a number of caterpillars can occasionally be spotted on roses in spring, such as the rose plume moth (Cnaemidophorusrhododactyla).There’s also the non-native rose leafhopper (Edwardsianarosae) which can cause faint speckling on leaves. Later in the growing season, rose chafers (Macrodactylus subspinosus) and the notorious Japanese beetle (Popilliajaponica) can be a concern.
Perhaps the most noticeable damage to roses in spring is caused by the larvae of sawflies.These insects cause two types of damage: “windowpane” damage when they only feed partway through foliage and leave the upper leaf surface intact or small holes or notches when larger larvae chew entirely through the leaves.In the Midwest, there are three different species of sawflies that can commonly be encountered on roses in spring: the roseslug sawfly (Endelomyiaaethiops), the curled rose sawfly (Allantus cinctus), and the bristly roseslug sawfly (Claudius diffiformis).To the naked eye, the larvae (up to ~ ½ inch long, pale greenish, and caterpillar-like) and the adults (~ ⅓ inch long, dark-colored, and wasp-like) all look similar.However, determining the exact species under magnification can be helpful to understand the potential impacts on your roses.
Classic “windowpane” damage caused by sawfly larvae on roses. This damage occurs when small sawfly larva only feed partway through the leaves. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.
The roseslug sawfly (Endelomyiaaethiops) is the commonest of the three sawflies that I see samples of at the UW Insect Diagnostic Lab.The larvae of this species have a smooth texture and brownish head capsule; their bodies are translucent and they usually have a pale greenish color due to ingested green leaf material. Some good news about the roseslug sawfly is that this species only has a single generation in spring.Their damage tends to be mostly just a minor cosmetic issue.As the plants really take off in late spring, they tend to “shrug off” this damage and it’s quickly covered up by new growth.
Larva of the roseslug sawfly (Endelomyia aethiops) feeding on the underside of a rose leaf. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.
The curled rose sawfly (Allantus cinctus) goes through two generations early in the growing season.Similar to the roseslug sawfly, their feeding damage tends to be minor and plants are usually able to chug along just fine.The larvae of the curled rose sawfly also are pale green with a brownish-orange head capsule.They do have tiny spots on their bodies, but these are only visible under high magnification. This species tends to feed while curled up and they also chew notches on the edges of leaves which can help distinguish this species from the other two sawflies.
Larva of a curled rose sawfly (Allantus cinctus) on the underside of a rose leaf. Note the notches on the edges of leaves which can serve as a clue to help identify this species. A rose leafhopper nymph is also present to the left of the larva. Photo credit: PJ Liesch, UW Insect Diagnostic Lab
The third sawfly commonly seen on roses also tends to be the most problematic—the bristly roseslug sawfly (Claudius diffiformis).Unlike the first two sawflies, this one can continue to reproduce throughout the growing season.Because they go through many generations per year, their damage can accumulate over time and tends to be more notable. Like the other two sawflies, the larvae of this species are also pale green with a brownish head capsule, but they are covered with fine, hair-like bristles when viewed under magnification. Very few sawflies have a hairy or bristly appearance like this, which helps distinguish this species on roses.
Larva of the bristly roseslug sawfly (Claudius diffiformis). Note the fine hair-like bristles which help identify this species as seen in this magnified photo. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.
If you do bump into these sawflies on your roses in spring, they’re pretty easy to deal with.Options for managing them include:
Do nothing. Since damage from the roseslug and curled rose sawflies tend to be minor, established plants often tolerate these insects with little/no intervention.
Squishing, hand-picking or knocking them into a container of soapy water (be mindful of thorns…)
Insecticidal soap or horticultural oils such as neem oil. Make sure to achieve good spray coverage.
Pyrethrins or spinosad—both are organic spray options. Note that Bacillus thuringiensis kurstaki (which works well against caterpillars) does not work against these sawflies.
Conventional sprays from the hardware store/garden center labelled for use on ornamental shrubs and landscape plants. Use caution since these products tend to have broader-spectrum of activity and can pose greater risks to bees and other pollinators such as butterflies, moths, beetles, and many flies.
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.
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
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…).
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.
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.
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.
Is the invasive spotted lanternfly (Lycormadelicatula) poised to be a problem in Wisconsin? Only time will tell, but the threat is definitely real.
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 (Ailanthusaltissima), 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, 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.
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.
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!
A heavy infestation of elongate hemlock scales. Heavy infestations can have significant impacts on conifers. Photo Credit: Eric R. Day, Virginia Polytechnic Institute and State University, Bugwood.org.
Elongate hemlock scale attacks over 40 species of conifers—especially hemlocks which can be common throughout the Appalachian Mountains, and Fraser firs and balsam firs, which are commonly grown as Christmas trees. Certain types of spruces and pines can also be attacked. Established populations of elongate hemlock scale are not known from Wisconsin, but a recent detection of this pest in the state raises concerns for Christmas tree growers, the plant nursery industry, tree care professionals, and homeowners with conifer trees in their yards. Forested areas are also at risk, meaning the stakes are potentially high with this insect.
While insect activity is quiet in the Midwest this time of the year, we’re hearing about the elongate hemlock scale now due to its Christmas connection. Similar to 2018, the Wisconsin Department of Agriculture, Trade and Consumer Protection recently found that fir Christmas trees, wreaths, and other holiday decorations infested with EHS had been shipped to Wisconsin from North Carolina. The picturesque Blue Ridge Mountains of western North Carolina provide ideal habitat for Fraser firs—one of the most popular species of Christmas trees. North Carolina grows approximately a quarter of all the Christmas trees sold in the US each year and with elongate hemlock scale established in that state, it increases the risk of movement of this invasive insect around the country.
The Blue Ridge Mountains near the border of North Carolina and Tennessee—the native habitat of Fraser firs. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab.
Elongate hemlock scales look unusual as far as insects go. These insects have traded mobility for defense—they hunker down on plants and produce a waxy coating which helps protect them from predators and parasites. As a result, elongate hemlock scales aren’t easily recognizable as insects since the usual signs of segmentation—body regions, legs, antennae—are not readily visible. Instead, these insects have a vague, oblong appearance. Adult females are small (just under 1/10th of an inch long) and are covered with a waxy brownish coating. They are typically found on the undersides of needles. Males are slightly smaller and develop beneath pale whitish coverings. Mature males do emerge with wings but are weak fliers and travel short distances to mate with the wingless, immobile females.
Two adult female elongate hemlock sales on the underside of a fir needle. Females are approximately 2 mm long. Photo Credit: Lorraine Graney, Bartlett Tree Experts, Bugwood.org
Under their protective coatings, these insects use needle-like mouthparts to suck fluids from plants. With their small size, damage occurs when large numbers of individuals infest plants. Their waxy coverings also limit the effectiveness of insecticides, making EHS a challenging pest to control if they become established.
Because elongate hemlock scale has been detected in Wisconsin this year in Christmas trees and other holiday decorations, a key objective at this point is to prevent this insect from getting a foothold in the state. By all means, continue to enjoy your holiday decorations, but when you’re ready to remove these materials, take the following steps to help prevent this insect from becoming established in Wisconsin:
1) If your Christmas tree or natural wreaths, garlands, or other decorations are from a local Christmas tree farm or elsewhere in Wisconsin, no special precautions are needed for elongate hemlock scale. Because EHS is not established in the state, these materials can be removed as usual at the end of the holiday season.
2) If your Christmas tree or natural wreaths, garlands, or other decorations are from a big box store, grocery store, or similar vendor, or if you are not sure of the origins of these materials, it is advised to check these materials for signs of elongate hemlock scale (i.e., brown spots on the undersides of needles). The Wisconsin Department of Agriculture, Trade, and Consumer Protection is advising that infested or suspect materials preferably be burned (check with the DNR for any burning restrictions in your area). Alternatively, such materials could be bagged and discarded as waste. Infested or suspect materials should not be composted or used for wildlife habitat in your yard.
For additional information on elongate hemlock scale, visit the WI-DATCP EHS page and the recent press release about the 2019 EHS detection.
A perk of being an entomologist is being able to better understand the world through the tiny creatures around us.However, this can also be a bit disheartening at times.While vacationing in Florida several years ago, I remember visiting the beach and the first three arthropods I encountered were out of place—a honey bee (originally arrived with Europeans), a millipede from Caribbean islands, and a weevil from Sri Lanka.I doubt any other beachcombers recognized the international gathering amongst the dunes that day.
A honey bee (Apis mellifera) on a Florida beach. Honey bees arrived in North America with Europeans and aren’t native to our area. Photo credit: PJ Liesch, UW Insect Diagnostic Lab
Seeing the world this way really reinforces the notion that humans play a critical role in the movement of species around the planet. Scientists can make their best predictions about invasive species, but there are plenty of surprises in terms of when and where a given species will turn up.For high priority invasives, designated surveys and inspections are conducted by government agencies to help monitor the situation.The general public can also play an important role in documenting the presence and distribution of invasive plants, insects, and other organisms.In Wisconsin, for example, the Wisconsin First Detector Network (WIFDN) uses a network of citizen scientists and a smartphone app to document invasive species.
White-spotted caterpillar of the purple carrot seed moth (Depressaria depressana) found in Middleton, Wi in July, 2019. Photo credit: PJ Liesch, UW Insect Diagnostic Lab
In some cases, invasive species are simply stumbled upon.Back in July, I bumped into the first case of the purple carrot seed moth in Dane county while riding some local mountain bike trails. Along these lines, my wife and I were walking our dogs in early November when I spotted some suspicious damage on a row of viburnum shrubs.A closer look revealed the distinctive feeding holes and egg pits of the invasive viburnum leaf beetle—the first evidence of an established infestation in Dane County.
Egg pits of the viburnum leaf beetle. Females chew small depressions in twigs of viburnum shrubs, lay several eggs, and cover the eggs with pits of chewed plant materials. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.
The first established case of the viburnum leaf beetle in Wisconsin occurred in 2014 in northern Milwaukee county and a more detailed account of this species can be found in the original post on this blog.Unfortunately, this invasive beetle has made some dramatic jumps on the map over the last few years—likely due to human movement of infested plant materials.Back in 2017, VLB was detected in Oshkosh (Winnebago Co.). In June of 2019 viburnum leaf beetle was spotted in Hurley (Iron Co.) in far northern Wisconsin and was detected across the border in Ironwood, Michigan shortly thereafter. Other detections in 2019, include Racine and Walworth counties.
Known distribution of the invasive viburnum leaf beetle in Wisconsin as of November 2019. Counties shaded in light blue had infestations known prior to 2019. VLB was detected in dark blue counties for the first time in 2019. Map: PJ Liesch, UW Insect Diagnostic Lab.
The viburnum leaf beetle can cause significant damage to viburnum shrubs and is already wreaking havoc in the greater Milwaukee area.Viburnums, including American cranberrybush viburnum, arrowwood viburnum, and others are widely distributed in both urban and natural settings, meaning that Wisconsinites now need to keep an eye out for this damaging insect in new parts of the state.
To learn more about the appearance, damage, and biology of the viburnum leaf beetle, visit the original post and this factsheet.
Author’s Note: Post updated in October, 2019 with the first confirmed report of lily leaf beetle in Pierce County, WI
It’s been a big year for the lily leaf beetle (Lilioceris lilii) in Wisconsin. The lily leaf beetle (or scarlet lily beetle) is an invasive Eurasian species that made its first appearance in the state back in 2014. This species originally showed up in North America around the time of World War II, arriving in eastern Canada with shipments of plant materials. It eventually spread into New England in the 1990’s and has been moving westward ever since. True to its name, this species has a fondness for lilies and can cause significant damage to true lilies (Lilium spp.), including both native lilies and cultivated types. Fritillaries (Fritillaria spp.) can also be attacked by the lily leaf beetle, as well as lily of the valley (Convallaria majalis) and Solomon’s seal (Polygonatum spp.) to lesser extents. Daylilies (Hemerocallis spp.), canna lilies (Canna spp.), and calla lilies (Calla palustris) are not attacked. The damage caused by lily leaf beetle can be severe. Since its arrival roughly five years ago, some commercial flower growers in parts of Wisconsin have stopped growing and selling lilies altogether.
A plant severely damaged by feeding activity of the lily leaf beetle. Photo credit: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
Adult lily leaf beetles are only about a quarter of an inch long but pack a punch when they chew irregular holes and notches in lily leaves, stems, and developing buds. If there’s a redeeming quality of this invasive insect, at least the adults are a conspicuous bright red color. However, when disturbed the beetles readily tumble from plants, and land upside down on the ground where they play dead. Their dark-colored underside makes them much harder to spot when this occurs.
Adult lily leaf beetle (Lilioceris lilii) and damage. Photo Credit: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
If it weren’t for their destructive nature, one might even consider the vibrant red beetles rather pretty. It’s hard to say the same of the larvae though. Lily leaf beetle larvae are a pale yellowish color with a black head capsule and approach nearly half an inch long. However, as a defensive behavior, the larvae typically camouflage themselves with their own excrement and look more like slimy greenish slugs or ooey-gooey animal droppings than insects. Just like the adults, the larvae cause significant damage as they chew holes and notches in lilies.
A slimy, excrement-covered larva of the lily leaf beetle. The larvae can cause significant damage to true lilies. Photo credit: Richard A. Casagrande, University of Rhode Island, Bugwood.org
While pests like the Japanese beetle don’t make their appearance until well into summer, the lily leaf beetle can be a threat throughout the entire growing season. This insect overwinters in the adult stage and the bright reddish beetles can emerge and start feeding early in the spring. After mating, female lily leaf beetles lay tiny reddish eggs on the underside of leaves. Eggs are often laid in batches of a dozen or fewer, but the long-lived females can lay hundreds of eggs in their lifetimes. The emerging larvae start feeding and can be common during spring and early summer. After gorging themselves for a few weeks, larvae eventually wander from plants to pupate in the soil. The next batch of adults will be present through the summer and fall months.
Map of Wisconsin with confirmed detections of the lily leaf beetle. Counties that are dark blue had their first official confirmed detection in 2019.
If you haven’t encountered this insect yet in Wisconsin, it’s not too surprising. The majority of the state has yet to see the lily leaf beetle—but that will likely change in the coming years. When it was first detected in the Wausau area in 2014, lily leaf beetle was found nearly simultaneously in a number of spots around the county, suggesting that it may have been spread by the movement of infested plant materials. Human movement of these insects remains an important factor today. Since its introduction, the lily leaf beetle has steadily been spreading around central Wisconsin through both human and natural movement. Alarmingly, in the summer of 2019, the lily leaf beetle made some significant “jumps” and was detected in Dane and Door counties. In early October, colleagues at DATCP confirmed the first detection of LLB from Pierce County. This discontiguous pattern on the map points to human movement as a likely cause. Unfortunately, these detections represent new footholds in Wisconsin and residents of those areas now need to be on alert for this invasive beetle.
In this post, we’re continuing to count down the University of Wisconsin Insect Diagnostic Lab’s top arthropod trends of 2018. This is the second half of a two part series; the first half can be found here.
5) White-Lined and Other Sphinx Moths:
The white-lined sphinx moth (Hyleslineata) can be a common species, so encountering one of the 3 inch long hornworm caterpillars isn’t unusual. However, these caterpillars can also be encountered in massive road-traversing hordes if the conditions are just right. From midsummer onwards, large numbers of these caterpillars were observed around the state—in some cases by the tens of thousands. If you didn’t spot any of the caterpillars themselves, you might have encountered the large adult moths with their hummingbird-like behaviour in late summer. Several other sphinx moths species also had a strong presence in 2018, such as the clearwing hummingbird moths and the tobacco and tomato hornworm caterpillars which can regularly be encountered in gardens as they munch away on tomato and pepper plants.
Large, dark-colored hornworm caterpillar of the white-lined sphinx moth. Photo submitted by Ted Bay, UW-Extension
4) Sawflies:
Sawflies, the caterpillar copycats of the insect world, are a diverse group, so they’re always present to some extent. Last year saw an unexpected abundance of two particular types in Wisconsin—the dogwood sawfly and the non-native Monostegia abdominalis, which feeds on creeping Jenny and related plants from the loosestrife group (Lysimachia species). While sawflies are plant feeders, dogwood sawflies can also damage the soft wood of a home’s siding or trim when these insects excavate small chambers to pupate in. The UW Insect Diagnostic Lab saw a distinct bump in reports of wood damage from the dogwood sawfly last year.
Larva of a dogwood sawfly showing the whitish, waxy coating. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab
3) Armyworms:
True armyworms (Mythimna unipuncta) can be a dynamic and sporadic pest in the Midwest. This species doesn’t survive the cold winters of our area, so adult armyworm moths must invade from the south each spring. Depending on national weather patterns, the arrival of the adult moths can vary significantly from year to year. If an early mass arrival is followed by abundant food and ideal conditions for the ensuing caterpillars, large populations can result. Once they’ve arrived, true armyworms can go through 2-3 generations in the state and this second generation of caterpillars made an alarming appearance in mid-to-late July. Under the conditions last summer, massive hordes of these caterpillars decimated crop fields before marching across roads by the tens or hundreds of thousands to look for their next meal. In some cases, that next meal included turfgrass, meaning that some Wisconsinites came home from work to biblical hordes of caterpillars and half-eaten lawns in late July.
Caterpillar of the True Armyworm (Mythimna unipuncta). Photo Credit: Lyssa Seefeldt, University of Wisconsin-Madison Extension
2) Monarch Butterflies:
Much to the delight of fans and conservationists, the iconic monarch butterfly (Danaus plexippus) appeared to have a banner year in the Midwest in 2018. Reports and observations of high numbers of monarchs poured into the Insect Diagnostic Lab during the summer months. As comforting as these reports were, the butterflies still faced a perilous 2,000 mile journey to reach their overwintering grounds in Mexico. The most consistent measurement of the eastern monarch population comes from estimating the area occupied by the densely-packed overwintering butterflies. In late January the latest count was released with encouraging news—the eastern monarch population is up 144% over last year and is estimated to be the largest in over a decade. In contrast, the western monarch population overwinters in southern California and has recently dipped to alarmingly low numbers. Regardless of the winter assessments, monarchs face tough challenges and Wisconsinites are encouraged to help conserve this iconic species. The Wisconsin Monarch Collaborative recently launched a website with resources for those wishing to join the effort.
Multiple monarch butterflies nectaring on a single plant in August. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab
1) Floodwater Mosquitoes:
Mosquitoes snagged the top spot on 2018’s list for good reason. The upper Great Lakes region is home to over 60 different mosquito species, but one subset—the “floodwater” mosquitoes—drove the storyline last year and impacted outdoor activities through much of the spring and summer months. Mosquitoes in this group, such as the inland floodwater mosquito (Aedes vexans), flourish when heavy rains come. Last year’s mosquito season kicked off in force with a batch of pesky and persistent floodwater mosquitoes just before Memorial Day weekend. Mosquito monitoring traps in southern Wisconsin captured record numbers of mosquitoes shortly thereafter. Later in the year, the Midwest experienced an unprecedented series of severe rainstorms, setting the stage for an encore performance of these mosquitoes. It was this second explosion of mosquitoes that caught the attention of anyone trying to enjoy the outdoors in late summer—a time of the year when mosquitoes are typically winding down in the state.
Ephemeral pools of water created ideal conditions for floodwater mosquitoes in late summer. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab
