Category Archives: Wood-attacking Insects

A Wood-Boring Insect Mystery

Imagine it’s August and as you wander in from your backyard, you notice a small pile of sawdust at the bottom of the door frame.  It might not be much sawdust, but you also find a few holes in the wood trim nearby.  It definitely seems to be insect damage, but who’s the culprit?

Unexpected insect damage to wood trim.

If you came up with a list of insects in the upper Midwest that can damage the wood of your home, it wouldn’t be terribly long.  For good reason, termites might be the first insect to come to mind, although our eastern subterranean termites are restricted to isolated pockets and are not commonly encountered in Wisconsin.  A close second on the list might be carpenter ants.  Interestingly, carpenter ants don’t technically eat (e.g., digest) wood and merely excavate soft, rotting wood to create a nesting site.  If anything, their presence in a home might be an indicator of a water damage.  Powderpost beetles can also attack wood and are commonly encountered in old barn beams and log cabins.  Carpenter bees help round out a list of the “usual suspects”.  These wood-boring bees can create good sized holes (a half inch across), although with their preference for unpainted softwoods used for trim, siding, and fence posts, their damage is mostly cosmetic in nature. 

Then another clue comes to mind—the nearby shrubs that had been eaten by some kind of worm-like insect over the past few weeks. 

Larva of a dogwood sawfly showing the whitish, waxy coating. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

When it comes to wood-damaging pests, sawflies generally don’t come to mind.  Sawfly larvae—Mother Nature’s caterpillar copycats—tend to feed on plant leaves.  Species like the European pine sawfly, dusky birch sawfly, rose slug sawfly, Columbine sawfly, pearslug sawfly, and birch leafminer sawfly can all be commonly encountered feeding on plants during the growing season.  One species that was common in 2018—the dogwood sawfly—is unique in that it not only causes plant damage but can also damage wood trim and siding of homes.  The dogwood sawfly is one of our commonest pests of native and landscape dogwoods (Cornus spp.).  When larvae are small,  they have a whitish waxy coating thought to mimic bird droppings and they can often be found curled up on the undersides of dogwood leaves.  As larvae mature, they lose the waxy coating and their black and yellow coloration becomes conspicuous.   

Mature dogwood sawfly larva with classic black and yellow appearance.

So how does this plant-feeding species end up damaging wood?  As is the case with any insect that undergoes complete metamorphosis, the larvae need to pass through the pupal stage to make it to adulthood. Insect pupae, however, are generally immobile can make an an easy meal for any predator that stumbles upon them.  Thus, many insects seek out tucked away spots to complete their pupal stage.  When ready to pupate, dogwood sawfly larvae typically create their own hideaway by chewing small chambers in rotting wood such as twigs, branches, or logs near the shrub they had been feeding on. 

Small chambers chewed into a fallen twig—a “typical” spot for dogwood sawfly to pupate.

If rotting wood is unavailable, the larvae may turn to other nearby wood materials—including wood trim and siding.  This typically occurs when larvae had been feeding on ornamental dogwood shrubs planted close to a home.  In the grand scheme of things, these insects don’t cause that much damage to wood, although homeowners won’t be thrilled if they’ve been caught off guard by this unexpected wood-damaging pest! 

Bobbleheads of the Insect World

During the winter months, I often get reports of intimidating-looking, but harmless and quirky wasp-like creatures known as “wood wasps” (Family Xiphydriidae).  What makes them quirky?—They’re basically the bobbleheads of the insect world, which always reminds me of going to baseball games as a kid.

Having “wasp” in the name can evoke a certain amount of anxiety, and you can already guess that wood wasps are related to the yellowjackets and paperwasps of late summer.  However, the wood wasps belong to an early branch within ant/bee/wasp group (the Order Hymenoptera) and lack the anatomical structures and ability to sting.

Side view of a “wood wasp” showing the scrawny “neck” and “bobblehead” appearance. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

Wood wasps have a distinct appearance, so once you’ve trained your eye, they’ll be hard to miss the next time around.  These insects tend to be about an inch long with slender, dark-colored bodies and orange legs.  There are often some pale stripes or patches on or just behind the head and in some cases the tips of the antennae can be pale as well.  The most diagnostic feature gives wood wasps their bobblehead status in my book—the bulbous head of these insects is attached by a scrawny “neck” when viewed from the side.  You can even imagine it bobbing back and forth, if only a tiny spring were attached.

You might ask yourself, how are these insect bobbleheads active in winter when most other insects are scarce?  The answer boils down to firewood.  The pale, grub-like larvae of wood wasps live in the wood of dead or dying trees.  When these trees are chopped into firewood, we end up hand-carrying the insects into our cozy winter abode.  If the wood isn’t used in the fireplace right away, the larvae take advantage of the spring-like conditions and transform into active adults indoors.  To those unfamiliar with wood wasps, you can scratch your head for days trying to find the source, but once you recognize them and their origins, moving the firewood to a colder location is the simple fix.

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.

Wisconsin’s Top 10 Insect Stories of 2014 (Part III)

Below you’ll find the third and final part of a series describing the Top 10 insect-related stories of 2014 from Wisconsin.


4) Hexagenia Mayflies and Fishing Spiders: If you love insects and/or fly fishing, you might have been thrilled to hear about the massive mayfly hatch along the Mississippi River in late July. These emergences happen yearly, but the mass emergence in the evening of July 20th was one of the largest in decades. We’re not talking about thousands or millions of insects, but billions of insects emerging at the same time. So many mayflies emerged simultaneously that the insects showed up on National Weather Service weather radar (read the full details here).  When these emergences occur, the insects can accumulate on bridges and streets making roadways slippery.

Hexagenia 20 July 2014
Mayfly emergence on the evening of July 20th. Source: National Weather Service.

The insect involved is the Hexagenia mayfly. The young (nymphs) live in the sediment at the bottom of the Mississippi River and feed on bits of organic matter in the water. The presence of the adults above water is truly an ephemeral phenomenon; it’s even reflected in the name of their group: the Order Ephemeroptera. Adult Hexagenia mayflies only live for a matter of hours, which leads them through a frenzied courtship period. Shortly thereafter, they’re done for.

Around the same time as the mayfly emergence, the fishing spider stories made their way around television, radio, and Facebook and the phone calls and emails came flooding in. Despite the hype, fishing spiders are native to Wisconsin and can actually be fairly common. Fishing spiders aren’t truly aquatic, but they do tend to hang out near water. They’re among our largest spiders in the state, and can be large enough to capture and feed on small minnows.

3) Spotted Wing Drosophila: One of our newest invasive species had another strong year in 2014. The spotted wing drosophila (SWD) is originally from parts of Asia, and was discovered in the US in 2008. Within two years, it had popped up in Wisconsin. Like other fruit flies, SWD loves fruit.  The main difference is that our run-of-the-mill fruit flies lay eggs in overripe or spoiled fruit.  In contrast, SWD females have a hacksaw-like egg-laying structure, which can be used to slice into ripe or ripening fruit to lay eggs. As a result, SWD has become a major issue for fruit growers in the state.  Late-season berry crops (raspberries, blackberries, strawberries) are hit the hardest. SWD has been found statewide, and will continue to be a major concern for late-season fruit growers for the foreseeable future.

2) Pollinators: You don’t have to listen to the news very long before you hear a reference to pollinators. Unfortunately, much of the news on the topic paints a bleak picture: pollinators of all kinds are in decline at the moment. Honey bees, bumble bees, other native bees, and butterflies like the Monarch are all facing declines. Unfortunately, it’s not a black-and-white situation, and there’s no simple solution to the issue at hand. Instead, many different factors, such as habitat loss, diseases, parasites, land-use practices, pesticides and other factors may all be involved one way or another.

We may not think of the connection to pollinators when we visit the grocery store, but without the pollination services of insects, the produce section would be scarce. It turns out that roughly a third of the world’s agricultural crops rely on pollinators. Without pollinators, you’d have a hard time finding apples, strawberries, melons, tomatoes, and many of our common food items.

Flowering plants in your yard provide resources to bees. Photo Credit: PJ Liesch
Flowering plants in your yard provide resources to bees. Photo Credit: PJ Liesch

If there’s a silver lining to the situation, it’s that attention has been brought to the topic. In June of 2014, the White House announced the creation of a pollinator health task force to develop a national strategy to help prevent pollinator losses and help improve pollinator habitat.  While it may seem like a small step, individuals can help pollinators by making their own yards pollinator friendly. Incorporating native plants into the landscape, providing nesting habitat for solitary bees, and using caution with pesticides are all ways to help pollinators in our own yards.  Tips for accomplishing this can be found here.

1) Emerald Ash Borer: The emerald ash borer (EAB) continues to be one of the biggest insect stories in the state. This invasive pest is originally from Asia, but has been wreaking havoc on Wisconsin’s ash trees since 2008. Spread within the state seemed to progress slowly at first, but 2014 saw dramatic changes in our quarantine map in the state. In early 2014, we had a total of 21 Counties quarantined for EAB. By the end of the year, 16 additional counties had been added to the map to bring the total up to 37 counties. While most of the quarantined counties are in the southern half of the state, Douglas and Oneida counties in the north are also quarantined. Unfortunately, this destructive pest is difficult to detect and easily transported in firewood, which means that this pest will only spread and the situation will worsen over time. While we have options to protect individual ash trees (available here), we don’t have a way to protect ash trees in woodlots or forested areas. Since its introduction into the US, the emerald ash borer has killed tens of millions of ash trees. With over 700 million ash trees in the state, Wisconsin has a lot at stake.