Category Archives: Crop Pests

2018’s Top Trends from the Diagnostic Lab (Part 2)

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 (Hyles lineata) 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 on a plant
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.

Whitish larva of the dogwood sawfly curled up on a dogwood leaf
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.

Striped caterpillar of the true armyworm
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.

Seven monarch butterflies nectaring on a flower
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

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?

Chinch Bug: How a Tiny Insect Helped the Rise of Dairy in Wisconsin

It was over 170 years ago that Wisconsin was granted statehood.  While much has changed over the decades, some things haven’t—like the omnipresence of agriculture.  It’s hard not to notice agriculture in Wisconsin, be it crop fields, orchards and vineyards, or our famous dairy farms dotting the landscape.  To many, Wisconsin is practically synonymous with dairy, and America’s Dairyland is even enshrined on our license plates.  While Wisconsinites may take our dairy prominence for granted, it turns out we weren’t always the Dairy State—at one point in history, you might have even called us the Wheat State.

It’s easy to understand why Wisconsin has a long history of agriculture.  The region received an influx of rich soil with the last ice age which allowed us to become a top wheat producer in the early days of statehood.  To early farmers in Wisconsin, wheat was a profitable crop in high demand.  For a period in the 1800’s, Milwaukee was even the busiest wheat shipping port in the entire world1.  Fast forward to today and Wisconsin is best known for its dairy production, while states like Kansas, Nebraska, and the Dakotas are known for their bountiful grains.

Quote from J.G. Thompson’s The Rise and Decline of the Wheat Growing Industry in Wisconsin2

It was the mid-to-late 1800’s when the course of Wisconsin’s history was forever altered by a number of factors.  Fluctuating wheat prices and overworked soil might have been the primary drivers, but dry weather and a tiny insect also pulled on the reins of history.  Just as mosquitoes can thrive after heavy rains, other insects thrive under hot, dry conditions.  Droughts of the 1860s, 70s, and 80s set the stage for biblical outbreaks of some of these insects.  Farther to the west, fields in the Great Plains fell victim to swarms of Rocky Mountain locusts so massive that they darkened the sky for thousands of square miles.

Closer to home, the pest delivering a coup de grâce to wheat fields was the humble chinch bug, which thrived under the dry conditions at the time.  Chinch bugs aren’t much to write home about: at roughly an eighth of an inch long, most folks wouldn’t take the time to examine these tiny, black and white insects.  It was by their sheer abundance that these creatures decimated Wisconsin’s wheat fields in the 1800’s.  Using needle-like mouthparts, these insects sucked the life out of wheat plants, leaving behind wilted, yellowed stems.

The chinch bug (Blissus leucopterus). Photo Credit: David Shetlar, The Ohio State University, Bugwood.org.

When a pest outbreak occurs in a given year, a farmer might chalk it up to bad luck, bad weather, or other factors and hope things improve the next season.  With falling wheat prices and chinch bugs regularly devastating wheat crops in the late 1800’s, Wisconsin wheat farmers realized that their efforts yielded little profit.  Without an effective way to prevent the ravages of the chinch bugs, attentions shifted to more fruitful possibilities.

The first comprehensive report on the biology and habits of the chinch bug.

Understanding the biology of the chinch bug was crucial to discovering the limitations of that insect’s destruction.  It turns out that chinch bugs are picky eaters with a taste for grasses—wheat, corn, and similar.  Unrelated plants, including forage crops like alfalfa, weren’t affected by these insects and could be grown to feed livestock at the very time that the dairy industry was budding in Wisconsin.  Decades later our dairy prominence is featured on our license plates.  

When enjoying those Wisconsin cheese curds, ice cream, and other dairy treats during national dairy month, chances are you probably wouldn’t have thought about insects—but now you know how the tiny chinch bug helped make dairy a BIG deal in Wisconsin.


1Harbor and Marine Interests. History of Milwaukee City and County Vol I. Ed. W.G. Bruce. 1922. Print.

2J.G. Thompson. The Rise and Decline of the Wheat Growing Industry in Wisconsin. Bulletin of the University of Wisconsin No. 292. Economic and Political Science Series. Volume V(3): 295-544. 1909. Print.