Category Archives: Invasive Species

Elongate Hemlock Scale: The Grinch Trying to Ruin Christmas

Christmas has come and gone in 2019, but an uninvited Grinch may still be lurking to steal the holiday spirit. The Grinch in this case isn’t the green gremlinesque being of Dr. Suess, but a tiny invasive insect known as the elongate hemlock scale (EHS). The elongate hemlock scale (Fiorinia externa) is native to Japan and was first detected in the US in Queens, New York over a century ago. Since that time, EHS has spread to 15 states in the eastern US.

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.
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.
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.

Insects on the Move: Viburnum Leaf Beetle

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.
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 beetlethe first evidence of an established infestation in Dane County

Egg pits of the viburnum leaf beetle on a viburnum twig.
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. 

Map of the the viburnum leaf beetle in Wisconsin.
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.

Red Alert for the Lily Leaf Beetle

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.

Severely damaged lily plants
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.

Lily leaf beetle adult
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.

Lily leaf beetle larva
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.

Wisconsin map showing counties with known lily leaf beetle activity
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.

Spring’s Coming…and so are the Insects

With daylight saving time beginning over the weekend and warmer temperatures knocking at our door, spring is finally crawling our way.  Last winter is one we won’t soon forget—the season started out mild before temperatures plummeted with January’s polar vortex.  During the coldest stretch, our coping strategy might have involved layers of blankets and reruns on Netflix, but what about the bugs? Questions regarding the winter impacts on insects have been some of the commonest at the UW Insect Diagnostic Lab this year.  There will undoubtedly be some impacts of this year’s polar vortex, although many insect species are well-equipped to deal with the cold.  Before we know it, overwintering insects will become active again in the Midwest and many species will simply shrug off the polar vortex as if it hadn’t happened.  For insects that didn’t fare as well in the cold, high reproductive capacities will likely allow their numbers to bounce back relatively quickly.

Thus, 2019 isn’t going to be insect-free by any means and intuitively this makes sense.  We know that every year insects make it through the winter months and become active as temperatures creep up in spring.  Looking at an evolutionary time scale, this year’s cold snap wasn’t the first time that the species in our area have encountered frigid temperatures before, and many creatures are adapted to survive surprisingly cold conditions.   We might have chosen to block it out of memory, but the Midwest experienced a very similar situation a mere five years ago.  Weather patterns in January of 2014 saw temperatures dip to -20˚F and colder in some spots of the Midwest.  The following summer, we still had plenty of insect activity in the region.

Thermometer from a cold and crisp Wisconsin morning. Photo credit: PJ Liesch, UW Insect Diagnostic Lab

Since we don’t see insects bundling up with tiny mittens and scarves, how do they make it through the winter?  It turns out that insects and other arthropods have a number of strategies to help them survive.  For starters, insects typically have a particular life stage (e.g., egg or pupa) that is more tolerant of adverse environmental conditions, such as freezing or desiccation.  Passing through the winter as a more resilient life stage is a good starting point.

Some of the other strategies are surprisingly similar to humans.  Just like snowbirds heading to warmer states for the winter, certain insects like monarch butterflies and green darner dragonflies migrate southward to avoid the coldest temperatures.  Our official state insect (the honey bee) doesn’t migrate, and instead chooses to remain active.  Honey bee colonies shiver together as an insect version of central heating to keep the inside of their hive a constant temperature.  Other insects simply seek shelter and overwinter in protected locations to avoid the worst of the cold.  Insects like the multicolored Asian lady beetle, boxelder bugs, and the invasive brown marmorated stink bug are fond of sneaking into man-made structures to spend the winter.  If insulation and central heating make homes warm enough for us, it’s plenty warm to prevent insects from freezing.  In more natural settings, such insects might end up sheltering in rock piles or beneath the loose bark of a dead tree.  Those locations might not be as toasty as a house, but they can still provide adequate respite from the cold—meaning that insects using this strategy should have been well protected from this year’s cold spell.  Similarly, many insects and other arthropods spend the winter below ground or on the surface of the ground amongst a layer of insulating leaf litter.  In addition, many parts of Wisconsin had a solid covering of snow by the time the polar vortex arrived, so creatures such as ticks had a thick layer of insulation from the coldest of the cold.

Another strategy utilized by insects is the production of natural antifreeze compounds (specific alcohols or proteins) which serve as cryoprotectants to help prevent freezing within their bodies.  We know that a cup of water will turn to ice at 32˚F, but dissolve salts or other substances in that same water and it will require colder temperatures to freeze it.  Insects producing high concentrations of these cryoprotectants can remains unfrozen at surprisingly low temperatures, similar to a bottle of high-proof spirits kept in a freezer.  Taking it even further, the common black and brown woolly bear caterpillars seem to embrace the cold and actually allow ice to gradually form within their bodies.  This may sound like a fatal mistake, but by regulating the formation of ice crystals on their own terms, woolly bear caterpillars are able to control where ice formation occurs and limit it to specific areas of their bodies to prevent damage.  If the same caterpillars were unprepared and froze rapidly, their cells might burst like a can of soda put into a freezer.

The ubiquitous woolly bear caterpillar (Pyrrharctia isabella) is well adapted to winter conditions. Photo credit: Dave Govoni via Flickr.

And then the ash borer
The insect I’ve gotten the most questions about lately has been the emerald ash borer.  While not native to our area, this invasive pest comes from similar latitudes of eastern Asia and the cold-hardy larvae are fortified with cryoprotectants as they spend the winter beneath the bark of ash trees.  These natural antifreeze compounds have their limitations though, and just like sidewalk salt failing to melt ice on a really cold day, the cryoprotectants only work down to certain temperatures before freezing (and death) occurs.  For emerald ash borer, the point at which freezing spontaneously begins to occur (the supercooling point) is when temperatures dip into the range of -13˚F to -23˚F.  This year’s polar vortex did see temperatures fall into and below that range, which would have killed plenty of emerald ash borer larvae, although the insulating effects of the tree bark likely provided some buffering.

The pale end of a surviving emerald ash borer larva sticking out from its tunnel. When larvae are killed by freezing, they typically become discolored. This sample came from the Milwaukee area in early March, 2019. Photo credit: PJ Liesch, UW Insect Diagnostic Lab

Emerald ash borer populations will almost certainly take a hit from this year’s polar vortex, but it’s not going to be a knockout blow.  Give it some time and the reproductive capacity of this invasive species will allow populations to rebound.  The news reports of cold-induced EAB mortality in early February might have been encouraging, but scientific models from the US Forest Service suggest that to really knock down EAB in the long run, we’d have to experience arctic blasts on a regular basis—news that many Midwesterners aren’t likely to receive warmly.


Further Reading: For a great read on how wildlife survive the winter, check out Bernd Heinrich’s Winter World

2018’s Top Trends from the Diagnostic Lab (Part 1)

Each year the University of Wisconsin’s Insect Diagnostic Lab receives thousands of arthropod samples and reports from around the state and region, providing a unique perspective into insect and arthropod trends in Wisconsin and beyond.  This post is the first half of a series counting down the top arthropod trends in our area last year.  The second part will be posted in early February and can be found here.


10) Dagger and Tussock Moths:
A few species of fuzzy caterpillars were surprisingly abundant last year and there’s a good chance you might have bumped into these in your own neighborhood.  Two similar-looking yellowish species, the American dagger moth and the white-marked tussock moth, were extremely common around Wisconsin and were two of the most widely reported caterpillars last summer. Another tussock moth associated with milkweed was also surprisingly common in 2018. With many Wisconsinites growing milkweed to attract monarch butterflies, the black and orange caterpillars of the milkweed tussock moth were also noted in abundance around the state last year.

Fuzzy black and orange Caterpillar of the milkweed tussock moth (Euchaetes egle)
Caterpillar of the milkweed tussock moth (Euchaetes egle). Photo Credit: Katja Schulz via Wikipedia

9) Fungus Gnats:
Pick any spot on a Wisconsin map and 2018 was most likely a soggy year. Understandably, rain encourages insects and other creatures that thrive under damp conditions. Last year’s rains created great conditions for fungus gnats, which became quite abundant by late summer. While fungus gnats are harmless to people and pets, they can be an annoyance if present in high numbers. Fungus gnats thrive in damp organic materials, meaning that rich soil, compost piles, and decaying plants can produce masses of these tiny, dark-colored flies. The larvae of these insects can also be common in the soil of houseplants.  As Wisconsinites brought their favorite potted plants indoors in autumn to avoid approaching frosts, reports of indoor fungus gnats were common.

Small dark coloured gnats captured on a yellow sticky card trap
Tiny (2mm long) fungus gnat adults captured on a sticky card trap near indoor plants in fall of 2018. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

8) Purple Carrot Seed Moth:
With several new, non-native insects showing up in Wisconsin every year, the impacts of each species can vary significantly. Some exotics, like the emerald ash borer make massive waves, while others cause merely a ripple. The impacts of one of our newest invasive insects, the purple carrot seed moth (Depressaria depressana), are not yet fully known. This European species was spotted in Wisconsin for the first time last summer and the tiny caterpillars love to feed on the flowers (umbels) of plants from the carrot family. Below-ground plant structures (e.g., the taproots of carrots) aren’t impacted, but notable damage to herbs like dill, fennel, and coriander can occur. As a result, this pest may be a concern for seed producers, commercial herb growers, or home gardeners with a fondness for dill and related herbs. The purple carrot seed moth has been reported in 8 Wisconsin counties thus far [Brown, Columbia, Dodge, Kewaunee, Milwaukee, Racine, Sheboygan and Washington Counties], so new county-level reports are encouraged at the UW Insect Diagnostic Lab.

Tiny (<1/4" long) spotted caterpillar of the purple carrot seed moth on dill.
Caterpillar of the purple carrot seed moth. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

7) Odorous House Ants
Imagine the stereotypical black ants zeroing in on sugary foods at a picnic and you’d have a fitting profile of the odorous house ant (Tapinoma sessile). Of the 100+ ant species in the Midwest, the odorous house ant stood out in spring and early summer last year with its sheer abundance. The UW Insect Diagnostic Lab was flooded with calls about these sugar-loving ants during 2018’s rainy spring, especially when these ants wandered indoors. The spring rains may have forced the ants from waterlogged colonies to seek out higher-and-drier locations, making odorous house ants the most commonly reported ant at the diagnostic lab last spring.

SMall black ant—an odorous house ant worker
Odorous House Ant (Tapinoma sessile) worker. Photo Credit: JJ Harrison via Wikipedia

6) Stink Bugs:
While the Midwest is home to over 50 species of stink bugs, one particular species—the invasive brown marmorated stink bug—stands out to give the rest a particularly bad reputation. If you live in a part of the state with the brown marmorated stink bug, you may have already encountered this species. With its habit of sneaking indoors in the fall, this insect replaced boxelder bugs in some areas as the top home-invading nuisance pest of 2018. This Asian species has made the diagnostic lab’s Top 10 list for several years now and unfortunately doesn’t show any signs of slowing down. In 2018 alone, BMSB was detected in 8 new Wisconsin counties, which hints at potential damage to fruit and other crops in those areas in the coming years.

Adult brown marmorated stink bug
Adult brown marmorated stink bug. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab


To see the rest of Wisconsin’s top arthropod trends of 2018, check out part 2, available here in early February.

2018 Update: Brown Marmorated Stink Bug in Wisconsin

Author’s Note: Original post updated in January, 2019 due to a confirmed report in Waupaca Co. and suspected report in Oneida Co.


One of the most concerning invasive insects to appear in Wisconsin in the last decade is the brown marmorated stink bug (Halyomorpha halys).  This Asian species delivers a double-whammy of not only damaging crops and other plants, but also being a significant nuisance when it sneaks into buildings in the fall. Since its initial detection in the state in 2010, populations of this insect have built up slowly but steadily. 

Brown marmorated stink bug adult on the side of a building in fall. This is becoming a common site in some parts of the Midwest. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab.

What’s the current status of BMSB in Wisconsin?

As of late 2018, 28 counties have confirmed reports of the brown marmorated stink bug and a handful of other countries have suspected sightings.  This insect has a strong foothold in the state and was confirmed in eight new counties in 2018 alone—Eau Claire, Jackson, La Crosse, Marquette, Monroe, Richland, Trempealeau, and Waupaca counties. 

Distribution of the brown marmorated stink bug in Wisconsin—updated January 4th, 2019
Distribution of the brown marmorated stink bug in Wisconsin—updated January 4th, 2019. BMSB has been confirmed in 28 counties. Map Credit: PJ Liesch, UW Insect Diagnostic Lab.

Two core areas currently stand out for brown marmorated stink bug activity in Wisconsin: the Highway 41 corridor from Fond du Lac up to Green Bay and southern Wisconsin from Dane and Rock Counties east to the Milwaukee metro area.  These two areas have the longest history of BMSB in the state and account for the majority of reports thus far. 

Much of the state has yet to encounter this insect or truly experience its impacts.  When the brown marmorated stink bug is first detected in an area, there’s a proverbial “calm before the storm”.   The pattern observed in the state thus far has been a few “quiet” years where low initial populations of this insect result in only a few sightings annually.  However, after a few years in a given area, BMSB populations build up to the point where nuisance problems around structures are noted and reports of potential plant damage begin to trickle in.

What’s the Outlook for BMSB?

Unfortunately, Wisconsin has yet to see the full impact of this invasive insect.  Observations over the last few years have found that BMSB is able to survive our winters and reproduce in the state, so this adaptable pest will most likely continue to build its numbers in the coming years. 

Over time, the brown marmorated stink bug is likely to emerge as one of the top structure-invading pests in the state alongside the likes of boxelder bugs and multicolored Asian lady beetles.  In the eastern US, where BMSB has been established for over a decade in spots, problems can be significant.  In some cases these malodorous insects have been documented invading homes by the tens of thousands

Several brown marmorated stink bug juveniles on a dogwood shrub. Ornamental trees/shrubs, vegetables, and fruit crops can all be attacked by this insect. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab.

While widespread crop damage has not yet been observed in Wisconsin, it may only be a matter of time as population of this insect continue to build in the state.  Agricultural problems have also been significant in the eastern US, giving us a glimpse into what could potentially happen in coming years.  For example, brown marmorated stink bug caused $37 million dollars in losses to apples in the mid-Atlantic states in 2010 alone.  

Having been detected in Portage County in 2017, brown marmorated stink bug may soon start to pose a threat to vegetable production in central Wisconsin.  Similarly, specimens confirmed from Door County in 2017 are forcing fruit growers in that part of the state to keep a close watch on their orchards and vineyards.  With the recent detection of BMSB in several western Wisconsin counties, we’ll likely see BMSB populations slowly build in that part of the state over the next few years as well. 

What should you do?

Purple Carrot Seed Moth Appears in Wisconsin

In a given year at the UW Insect Diagnostic Lab, I typically document 2-3  new, non-native, potentially-invasive insects in Wisconsin. In some cases, these species make an appearance only to fade into the background with little impact, while other exotics become heavy-hitting invasive pests (e.g., emerald ash borer and gypsy moth). The latest non-native pest to make an appearance in the state is the tiny “purple carrot seed moth” (Depressaria depressana) and its impacts are not yet fully known. This species has a wide native range and can be found from western Europe through Russia to China.  It was first documented in North America in 2008 and is so new that few images exist and it’s not included in the common caterpillar and moth field guides on the market.

Purple carrot seed moth. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

In the last decade, the purple carrot seed moth has been documented in many locations in southern Canada and the northeastern US and has also been spotted in a few scattered locations in Michigan, Indiana, and Illinois. In mid-July of 2018, two reports came into the UW Insect Diagnostic Lab in rapid succession—Kewaunee and Dodge counties in Wisconsin. These cases were confirmed through images and caterpillar specimens that were reared to adult moths. After discussing the purple carrot seed moth on a recent episode of Wisconsin Public Radio’s The Larry Meiller Show, several additional suspected cases were reported in the state: Racine (Racine Co.), Random Lake (Sheboygan Co.), Burnett (Dodge Co.), and Franklin (Milwaukee Co.).

These insects get their name due to their association with flowers (umbels) of plants in the carrot family (Umbelliferae). The caterpillars of the purple carrot seed moth are small (3/8 inch long when mature), but dozens can feed on a single umbel. The caterpillars are dark green or reddish with many conspicuous white spots on their bodies. In addition to feeding on the flowers, the caterpillars tie together floral parts with silken webbing, which can make herbs like dill unusable. Eventually the caterpillars pupate within the webbing and emerge as adult moths a short time later. The adult moths are 3/8 inch long with a pale patch near the head; their purplish-grey wings are folded back along the body when not flying.

Caterpillar of the purple carrot seed moth, note the many conspicuous white spots on the body. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

The impacts of this non-native insect are not fully known for our area. The reports of plant damage in Wisconsin thus far have only been on dill. Due to the plant parts attacked (flowers), the impact on carrots, celery, and parsnip crops will likely be minor. The biggest impacts would be expected with umbelliferous crops commonly grown for seeds: dill, fennel, and coriander. Luckily, several organic control products may offer help on herbs: insecticidal soap and Neem oil are two low-impact products expected to help control this pest, if needed.  Cutting out and destroying infested flower heads may be another helpful tactic.

Damage from the purple carrot seed moth on dill. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

Because this pest is “new” in Wisconsin, if you believe you’ve found it on dill or other plants from the carrot family, please snap some pictures and contact me to help document this species in the state.

If you’d like to learn more about this insect and its potential impacts check out this video through the Wisconsin First Detector Network.


May 2019 Update: A current distribution of known PCSM sightings can be found below.  If you encounter this insect this summer in Wisconsin, feel free to let me know, so I can better keep track of its activity in the state.        —PJ

County records of the Purple Carrot Seed Moth from 2018. Map Credit: PJ Liesch, UW Insect Diagnostic Lab

To Boldly Go Where Man Has Gone Before: Pests on the Move

Since the earliest days of mankind, we’ve excelled at exploring and expanding our presence to nearly every spot on the map With all our wanderlust, we’ve been equally adept at taking other species with us as we go—often with unintended consequences. 

In some situations, species have been deliberately moved by humans: livestock to the new world, the introduction of birds from Shakespeare’s plays into Central Park,  and even the notorious gypsy moth was transported from Europe in a failed attempt at an American silkmoth industry On top of that, there’s an extraordinarily long list of species that have been accidentally moved, with significant impacts Stowaway rats on the ships of European explorers and traders would be one of the most notorious examples Rats introduced to new island environments wreak havoc on native birds and reptiles by devouring vulnerable eggs Insects have also been transported around the globe with devastating results and some of North America’s most important and emerging insect pests originate elsewhere on the planet: Japanese beetle, emerald ash borer, brown marmorated stink bug, and the spotted lanternfly.

Aedes sp. mosquitoes preparing for a blood meal.  Photo Credit: Ary Farajollahi, Bugwood.org.

One of the insects best adapted to follow humans is the notorious mosquito Certain mosquito species (peridomestic species) possess traits that allow them to take advantage of conditions in areas disturbed by humans and thrive in those spots.  With humans came environmental modification, construction, and discarded trash of one kind or another.  Some mosquitoes might have originally relied on the water pooled in natural containers, such as rotted out tree stumps to reproduce, but can just as easily take advantage of water-filled containers, ditches, and other artificial habitats.

In modern times, automotive tires have become a key habitat for certain mosquito species Tires not only are perfect objects for holding water for extended periods, but they also provide the dark, sheltered habitat favored by some female mosquitoes looking to lay eggs Tires are an important way for mosquitoes, like the Asian Tiger Mosquito (Aedes albopictus) to be moved into and around the US (including the Midwest) Other species, like the Asian Rock Pool Mosquito (Ochlerotatus japonicus), are also easily transported in human materials.

Hyacinth flower sold from a local store, including a vase pre-filled with water. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.

A recent case at the UW Insect Diagnostic Lab illustrates the ease with which non-native mosquitoes can be moved around the country In the first part of 2018, stores have been selling hyacinth bulbs in vases pre-filled with water as a way to force the bulbs to bloom into a flash of color during the dreary winter months In a recent discovery in southeastern Wisconsin, a vase purchased at a local store ended up yielding half a dozen larvae of the non-native Asian rock pool mosquito.  The exact origin of the mosquitoes isn’t known at this time.

A bonus surprise with the flowers—larvae of the Asian rock pool mosquito (Ochlerotatus japonicus). Animation credit: PJ Liesch, UW Insect Diagnostic Lab.

These mosquitoes won’t be much of a concern in the grand scheme of things as Ochlerotatus japonicus has been present in Wisconsin for over a decade and is already established hereHowever, such cases do leave open the possibility of non-native mosquitoes being moved into parts of the country where these pests have not been encountered beforeWhere humans go, pests will boldly follow.

Under the Microscope: Arthropod Trends of 2017

Over 2,500 cases flowed through the doors of the UW Insect Diagnostic Lab last year, ranging from the typical June beetles through bizarre creatures that most humans will never see in their entire lives (like the itch-inducing pyemotes grain mite).  Perhaps Forrest Gump said it best when he quipped, “life was like a box of chocolates—you never know what you’re gonna get.”  A distinction amongst insects, however, is that the “box” contains 20,000+ possibilities in Wisconsin alone and over well 1,000,000 globally.  With that said, a year at the UW Insect Diagnostic Lab is like having one humongous, box of really awesome chocolates, without all the calories.

Finding a pyemotes itch mite is like trying to find a needle in a haystack, except in this case these microscopic mites were in a farmer’s batch of corn. Photo credit: PJ Liesch, UW Insect Diagnostic Lab

With insects and related creatures, the weather can of course have a big impact and there definitely were examples of this in 2017.  The current cold winter aside, the last two winters had been otherwise mild, giving a few insects suited for warmer conditions a chance to inch their way northward.  Last spring and summer, this meant a bunch of sightings of an otherwise uncommon bee for our area known as the carpenter bee due to its habit of tunneling into unpainted cedar trim and other wood.  In a typical year, I might see a few cases out of the southeastern corner of Wisconsin, but 2017 had regular reports of these bumble bee look-alikes during the spring and summer months.  Similarly, praying mantids often meet their maker at the hands of a cold winter, but were surprisingly abundant in late summer and fall of last year.  Ticks were also extremely abundant last spring and with the rainy start to the summer, mosquito numbers were at an all-time high in some traps.  Mosquitoes were also a big deal in the news, with Wisconsin’s first confirmed reports of the Asian Tiger Mosquito last July.

Asian Tiger Mosquito (Aedes albopictus). Photo credit: James Gathany, Centers for Disease Control

The creature that amassed the most phone calls and emails in 2017 was the notorious Japanese beetle, which likely also benefited from the warmer than average winters these past few years.  For Wisconsin gardeners and farmers, the Japanese beetle is certainly a formidable foe, but at least there are ways to mitigate the damage.  In contrast, there’s another destructive pest wiggling its way into the spotlight in the state, which is much more difficult to control—an invasive earthworm commonly known as the jumping worm.  While they may not be insects, these earthworms are creepy-crawly and can wreak havoc in  gardens and flower beds, so I received a fair number of reports and questions.  What stood out to me in last year was the rapidity with which these destructive worms have been moved around the state (moved—as in humans have moved soil, plants, mulch, and similar materials).  Jumping worms were first found in the state in 2013 (in Madison), but have now been spotted in roughly half of the counties in Wisconsin.  To make matters worse, we don’t have any highly effective tactics to prevent these worms from turning rich garden soil into the consistency of dry, crusted coffee grounds—gardeners beware!

Speaking of invasive species, the emerald ash borer has continued its march through the state and now has footholds in some of our northern counties including Chippewa, Douglas, Eau Claire, Marathon, Marinette, Oneida, and Sawyer counties.  Unfortunately, our greatest concentrations of ash trees are in the northern part of the state (e.g. black ash in swampy areas), and the loss of ash from northern wetland areas could result in significant ecosystem effects.  Other recent invaders like the spotted wing drosophila and the brown marmorated stink bug had busy years as well.

Rusty patched bumble bee (Bombus affinis) visiting a flower in Middleton, WI. Photo credit: Rick Terrien

In other insect news, it seemed to be a good year for monarch butterflies in 2017, and the rusty-patched bumble bee finally made it onto the federal endangered species list. I was pleasantly surprised by a number of confirmed sightings of the rusty-patched bumble bee in the state as well. Perhaps my favorite “bug” story for the year involved black widow spiders.  It’s not common knowledge, but we do technically have a native black widow species in the state (Northern Black Widow, Latrodectus variolus).  It’s a reclusive species and is rarely encountered in Wisconsin, but reports trickled in once or twice a week at some points during the summer months (details to follow in a future blog post).

With so many cases last year, we’re really only touching the tips of the antennae.  If you’re interested in hearing more of the unusual stories from the UW Insect Diagnostic Lab, I’ll be giving a “highlight” talk on May 4th on the UW campus.

 

 

 

Weathering the Emerald Storm: EAB in Wisconsin

Like a kid watching a summer thunderstorm slowly rolling in and wondering how long until the rumbles would be directly overhead, I’ve had a morbid fascination with watching the progression of the emerald ash borer in the Midwest for over a decade.  Although emerald ash borer wasn’t found in Wisconsin until 2008, my connection with EAB precedes that by a few years.  It turns out my first job as a budding entomologist was as a summer intern for UW-Extension looking for signs of the insect in the state during the summers of 2005 and 2006.  Fast forward twelve years and that storm is finally overhead, at least in my neck of the woods.  I knew such a time would come, but it really hits close to home when the sounds of chainsaws mark the final days of your neighborhood’s ash trees—at least the ones that aren’t being treated. 

EAB Detection and Quarantines as of May 19, 2017. Click for larger version. Image source: WI-DATCP.

At the time of writing, 42 counties in Wisconsin have been quarantined for EAB.  While the southeastern part of the state has already been hit hard (green on the map above), a large chunk of the state has not yet seen the emerald ash borer or has only seen light pressure (click the map above to see more details on this topic). Unfortunately, this means that the emerald storm will only be getting worse over the coming years.  Along these lines, when EAB first arrived in Wisconsin, spread was slow and the annual number of new community-level detections was small.  However, as the populations of this insect have built up in the state, the number of new detections has increased dramatically as illustrated below:

Chart created using data from WI-DATCP on May 22, 2017. Click for a larger version.

Unfortunately, the outlook for the Midwest’s ash trees doesn’t look good and we’ll still be dealing with this insect for years to come.  Ironically, this isn’t the first time that we’ve watched a scenario like this play out.  As the baby boomer generation grew up, they watched as elms were devastated by the likes of Dutch elm disease.  As with emerald ash borer, Dutch elm disease had significant impacts on forested and urban areas and led to irreversible changes in the landscape around us.

With all this Doom-and-Gloom, is there a light at the end of the tunnel?
Possibly—but it may be a ways off.  For the time being, there are insecticide treatments available that can maintain the health of ash trees, although treatments are costly and are only feasible for relatively small numbers of trees.  Biological control is being explored as a potential way to control EAB populations, although results have been limited thus far.  However, with any biological control program, it can take years to work the kinks out of the system and see results.

A long-term plan may be to develop varieties of ash trees that are resistant to attack by the emerald ash borer.  In several locations in Ohio and Michigan, scientists have found a small percentage of “lingering” ash trees that have survived the initial onslaught of EAB and are monitoring those trees over time for continued survival and genetic traits that may help stave off infestations.  Interestingly, one particular species of ash (blue ash, Fraxinus quadrangulata) may hold important clues for long-term ash survival.  In some spots in Michigan, >60% of blue ash trees have survived in areas attacked by emerald ash borer.  While tree breeding programs may ultimately develop a resistant ash variety, this is likely years away and for the time being we’ll have to face the emerald storm.

Larval tunnels of the emerald ash borer beneath the bark of an ash tree. This damage disrupts the flow of water and nutrients and ultimately kills the tree. Image source: PJ Liesch, UW Entomology.