Tag Archives: Featured

Caterpillars, IDL Highlights, Moths, Odd Insects

Snow Falling on Cutworms

When most folks think of “cutworms” they probably envision big fat caterpillars munching on plants in their yards and gardens.  Sure enough, we have many species from the cutworm & armyworm family (Family Noctuidae)  that can be notable crop pests, such as black cutworm, bronzed cutworm, variegated cutworm, true armyworm, fall armyworm, and others.  Readers should keep in mind that the Family Noctuidae is surprisingly diverse with over 2,500 species known from the US and Canada.  Many of these species play important roles in the food web and can be as important as bees for pollination of certain crops!

While cutworms can be common during the summer months into the fall, we usually don’t expect to see them this time of the year.  Surprisingly, there’s one cold-hardy species that has been common in Wisconsin recently—the “winter cutworm” (Noctua pronuba).  This species gets its name due to the fact that the caterpillars are cold-tolerant and can be active when temperatures dip.  While they won’t be out-and-about during a polar vortex, I’ve had many recent reports at the UW Insect Diagnostic Lab of winter cutworm caterpillars wandering on the snow when temperatures have been in the 20’s.  Overall, there are very few caterpillars that venture onto the snow, period.

Winter cutworm caterpillar wandering on the snow. Photo submitted to UW Insect Diagnostic Lab in late 2022.

Similar to other cutworms, the winter cutworms are plump, earth-toned caterpillars—they are brownish with pairs of black dashes bordered by white running down the sides of their backside, which makes them easy to identify.  (Technically, a greenish form of the caterpillars also occurs). In addition, if you see any caterpillar that even looks “cutworm-like” out on the snow, it’s almost certainly this species.  They pass through the the winter as nearly-mature caterpillars before pupating in the spring.  The adult moths are active during the warmer months and display an amazing array of different color forms—ranging from very light beige to grey or brownish—although the hindwings (typically tucked under the body at rest) are a diagnostic yellow color.  Thus, adults are commonly known as “large yellow underwing” moths.

Larger yellow underwing moth showing the distinctive yellow color of the hindwings. Photo credit: Olaf Leillinger via Wikipedia CC.

The winter cutworm can be found from coast-to-coast in much of the US and Canada, although this wasn’t always the case.  This species is common in Europe and wasn’t known from North America until 1979 when it was first spotted in Nova Scotia.  While the caterpillars do feed on a wide range of plants, they’re rarely a notable pest.  Outbreaks and reports of damage aren’t common, although there was a notable outbreak in Michigan around 2007-2008.  In most cases, these caterpillars are simply a curiosity as they wander across the snow on mild winter days—sometimes by the thousands.  In addition, winter cutworms can occasionally sneak into structures as well, which can be another surprise to see caterpillars actiely wandering in garages or barns when the temperature is in the 40’s.

Winter cutworm caterpillar found in a garage last December. Photo submitted to UW Insect Diagnostic Lab.
Flies, Indoor Flies

Blow Flies (Calliphoridae) Indoors

Each insect species has a “story” to tell—where they came from, what they do, and what their presence means for humans. Knowing this story can make a big difference when it comes to our own actions.  For example, imagine finding an insect near your bed.  If you recognized the insect as a harmless ground beetle that accidentally snuck in from outdoors, you might shrug your shoulders and carry it outside in a Tupperware.  But, if the insect were a blood-feeding bed bug, it could mean an expensive bill to have your home professionally inspected and treated by a pest control company.  Knowledge is power!

In my mind, the first step towards getting this knowledge is through proper identification.  I say this with a certain amount of endearment, as I am an insect diagnostician after all.  However, once you’ve properly identified an insect, it’s easy to look up its “story” (biology, behavior, etc.) in books, websites, or even the scientific literature.  This process can allow you to more efficiently identify the root of a problem (if there is one) and figure out a solution.

Adult cluster fly (Pollenia sp.)
A cluster fly (Pollenia sp.). These flies are common parasites of earthworms, but frequently enter structures in late summer and can be a nuisance. Preventing their entry into homes is the single most important management step. Photo credit: Katja Schulz, via Wikipedia.

A good example of this concept would be flies in and around homes.  There are easily dozens of different types of flies that can be encountered in typical yards and homes in the Midwest and each has a slightly different story to tell.  Some can breed in piles of grass clippings or seaweed (e.g.,  stable flies), some parasitize earthworms but like to sneak indoors (e.g., cluster flies), and others can hitchhike on plants.  A common and widespread group of flies is the Family Calliphoridae—the blow flies.

Luckily, blow flies can be identified easily in many cases due to their metallic green or bluish coloration. Some members of this group are even known as “green bottle flies” or “blue bottle flies” due to their distinctive colors.  Overall, the blow flies are mid-sized flies and are often slightly larger than house flies (~1/4 – 3/8” long).  The larvae are your stereotypical pale and slender “maggots”, although they can be definitively distinguished from similar-looking fly larvae under the microscope.

Adult blow fly (Family Calliphoridae)
An adult blow fly. The metallic green coloration is a helpful identifying feature. Finding these indoors often indicates a dead mouse. Photo credit: Brian Gratwicke via Wikipedia.

When blow flies are found indoors, it’s often easy to understand the situation and remedy the problem.  One of the biggest factors in the “story” of blow flies is dead stuff.  Out in nature, blow flies play an incredibly important role in helping break down dead animal matter.  These flies are often the very first insects to show up at dead animals—sometimes within seconds.  After laying eggs, the resulting larvae do a lot of work feeding on and breaking down animal tissues.  Being poikilothermic (“cold-blooded”), they also develop at a predictable rate depending on the temperature, so these flies are even used to estimate lengths of time in forensic investigations.

There’s always a chance that a blow fly spotted indoors might have accidentally snuck in from outdoors, but in many cases it’s an indication of something dead.  Blow flies are able to detect the faint odors of death from long distances, so a single dead mouse, bat, or other creature in a home can attract these flies.  Rather than spraying an insecticide, the best remedy is to find the root of the issue and clean it up.  In many cases, it’s just a matter of checking mouse traps and discarding the mouse that had recently met its demise.

Another situation that I often see indoors is a scenario that has simply proceeded further than the last one.  If an adult female blow fly is able to locate a dead mouse (or other animal) and lay eggs unnoticed, the resulting larvae can consume most of the remains and complete their development.  If this happens, the first thing noticeable is often a bunch of maggots wandering the nearby area (the maggots often wander away from their food source when ready to pupate).  When they pupate, small brownish “pods” (puparia) may be noticed and upon reaching maturity, dozens of adult blow flies can seemingly appear out of nowhere.  In such a case, it’s generally an indicator that a dead mouse or other animal had been present for some time (often a few weeks). Unless there are additional resources for them, these flies usually perish quickly indoors.  This scenario frequently comes into play in second homes or cabins that are unoccupied for longer periods of time or if the dead animal is location in a tucked away or inaccessible spot (such as in a wall or ceiling void).

Bugs, IDL Highlights, Outdoor Insect Invaders

Boxelder Bugs: Back in the Mix

If you’re like me, you’ve probably been out appreciating our recent fall weather.  Likewise, boxelder bugs (Boisea trivitatta) have also been enjoying the warmth.  I’ve seen an uptick in reports of boxelder bugs at the UW Insect Diagnostic Lab this year compared to most other years in the last decade and weather patterns in the Midwest have played an important role.

Adult boxelder bug
Adult boxelder bug (Boisea trivitatta) on the side of a building. Photo credit: PJ Liesch, UW-Entomology.

Whether you recognize them or not, there’s a good chance you’ve bumped into boxelder bugs before.  These black and red insects can be common throughout the warmer months and can be especially abundant in late summer and early fall.  Adults are approximately ½ inch long and have a criss-cross pattern on their backside created by their wings.  Juveniles (nymphs) are smaller with much more red on their bodies.  As the nymphs mature, their developing black wing pads become noticeable.  True to their name, boxelder bugs are commonly associated with boxelder trees (Acer negundo).  Botanically speaking, boxelders are technically a type of maple, and some other maples can also be a host for these insects as well as ash trees and a few others.  

Two juvenile boxelder bugs
Boxelder bug nymphs (juveniles) on the UW-Madison campus. Photo credit: PJ Liesch, UW Entomology.

From a plant-health perspective, boxelder bugs cause little damage to plants and are of little concern.  These insects get the most attention when they’re spotted on the sides of homes and other structures.  They’re often particularly fond of the southern and western sides of homes where the warm afternoon sun hits.  Boxelder bugs are often spotted on buildings in fall as they search for sheltered overwintering spots.  If they can squeeze in through a gap or crack, they can easily hunker down in a wall void, or similar spot for the winter.  Sometimes, boxelder bugs can make it to a location where they become active indoors during the winter months, much to the chagrin of the humans living in the home.  While these insects can be perceived as a nuisance, they’re really quite harmless to people, pets, and homes (although they could stain light-colored fabrics if crushed).  Like other “fall invading” insects (e.g., cluster flies, multicolored Asian lady beetles, brown marmorated stink bugs, and western conifer seed bugs), a helpful approach is to seal up potential entry points on the exterior of your home before these insects make their way inside.

A number of adult boxelder bugs on a window screen.
Boxelder bugs congregating on the side of a home. Photo submitted to UW Insect Diagnostic Lab.

Looking at long-term patterns, boxelder bug populations have generally been low in many parts of Wisconsin over the last decade.  A reason for this is moisture.  When we have rainy years, entomopathogens (insect-infecting pathogens) can keep boxelder bug populations low.  In contrast, boxelder bugs tend to thrive under drier and warmer conditions.  There’s even been research on a closely-related species (the western boxelder bug, Boisea rubrolineata) in the western US suggesting that those insects deliberately sunbathe and secrete a chemical to help inhibit the common entomopathogenic fungus Beauveria bassiana.  Here in Wisconsin 2021 was surprisingly dry in many areas which likely helped boost boxelder bug numbers.  Likewise, some parts of Wisconsin also saw dry conditions continue into 2022, which may have helped them further, leading to an increase in boxelder bug populations and reports this year.

Bugs, IDL Highlights

Large Milkweed Bugs: Featured Fall Insect

With the arrival of fall, we’re starting to see pumpkins, spooky yard decorations, and pumpkin spiced everything (*shudder*).  Not to be left out of the festivities, one insect can be quite noticeable this time of the year—the large milkweed bug (Oncopeltus fasciatus).

Large milkweed bug (Oncopeltus fasciatus) adult. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.

If you’re wondering, we do also have a small milkweed bugs (Lygaeus kalmii), although it’s not usually as common as the ubiquitous, larger cousin.  Both juveniles (nymphs) and adults of the large milkweed bug are fittingly adorned for fall.  Adults reach lengths of nearly 3/4  inch long and are mostly orange with black patches on the wings and body.  Going through “simple metamorphosis” (technically, they’re paurometabolous), the juveniles or nymphs look similar in body shape to adults (although smaller) and are also orange with some black.  In more mature nymphs, the developing blackish wing pads are quite noticeable.  When you see a group of nymphs and adults hanging out on milkweed in the fall, it’s easy to recognize that they’re all the same species.

Large milkweed bugs specialize on milkweed plants and are one of the many creatures that can be found in and around milkweed patches.  When they feed, large milkweed bugs use their sucking-type mouthparts to sip fluids from plants; they’re especially fond of the developing seed pods and are often spotted on pods.  While home gardeners hoping to rear monarchs might be concerned about competition, these insects generally cause little harm to plants and are more of a curiosity than a pest.

Group of large milkweed bugs (Oncopeltus fasciatus) on milkweed at UW-Madison; both adults and nymphs are present. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.

Large milkweed bugs have a very seasonal pattern in the upper Midwest.  They can’t survive the winter at more northern latitudes, so they must migrate northwards each year.  Here in Wisconsin, you’d be hard pressed to find large milkweed bugs in spring, but by July they’ve often arrived in low numbers.  Large milkweed bugs can become quite common by late summer and early fall as it typically takes 40+ days for a new generation of adults to appear from eggs laid in our area.

In much of Wisconsin, we’re just starting to see foliage change to reds, oranges, and yellows, but as you’re out enjoying the fall weather, keep an eye out for these festive-looking insects around milkweed patches.

Biting Insects, Medical Entomology, Pollinators

Do mosquito yard sprays harm other insects?

If you’ve noticed all the lawn signs for mosquito treatments, you may be wondering if mosquito yard sprays harm other insects. If so, you’re not alone.  As an Extension entomologist, this is a common question that I get from the public every year.  To get to the bottom of this question, it helps to understand the different types of mosquito spraying that’s done.

One approach (Ultra Low Volume or ULV) is sometimes used by municipalities or abatement districts to control mosquitoes.  These ULV applications generally involve using specialized equipment mounted on trucks or aircraft to apply extremely tiny droplets which kill adult mosquitoes by direct contact as the droplets float in the air.  Such applications use very small volumes of insecticides either undiluted or with minimal dilution and are often applied after dark when mosquitoes are most active.  The microscopic droplets from ULV treatments disperse relatively quickly and have little residual activity—think of them like a “one time strike” to knock down mosquito numbers.

The vast majority of research on mosquito sprays and non-target organisms has looked at these ULV-type treatments.  Some good news is that these studies suggest that impacts to non-target insects are relatively small and short-lived.  It turns out that the ULV treatments are most effective on insects with very small body mass, so insects larger than mosquitoes tend to be spared.  A good summary of the impacts of ULV treatments on non-target organisms can be found in a 2012 review paper by J.A.S. Bonds in Medical and Veterinary Entomology. 

Many mosquitoes like to rest on vegetation during the day, so some mosquito sprays specifically target these resting sites. Photo credit: Public Domain Image.

Case closed, right?—Not quite. Here in Wisconsin, we don’t really use ULV treatments a whole lot for mosquitoes.  The common yard treatments are what we’d call “perimeter”, “barrier”, or “residual” treatments.  Such treatments are applied via a backpack sprayer to create a coating or “barrier” on treated surfaces which affects mosquitoes that land on it.  These treatments involve applying a residual insecticide (usually from the pyrethroid group) to vegetation in yards and around structures.  The pyrethroid products are broad-spectrum and often last for a few weeks or longer depending on the formulation.  These same ingredients (and sometimes the exact same products) can also be used to control a wide range of yard, garden, and structural pests (e.g., Japanese beetles, garden pests, household ants, etc.).

While the pyrethroids are very common and widely used for a range of purposes, there’s a knowledge gap when it comes to the impacts of mosquito “barrier” treatments on other insects.  While this knowledge gap exists, a few studies raise concerns.  One study by Dr. Karen Oberhauser and colleagues found that monarch caterpillars could be harmed or killed even 3 weeks after spraying.  A more recent (2022) study by Qualls et al. found that honey bees were harmed 28 days after “barrier” treatments were applied.  Thus, if a yard is being sprayed for mosquitoes monthly during the warm season, there are reasons for concern.  More research is needed to help understand the effects of these “barrier” yard treatments on insects that often land on vegetation in yards, such as moths, butterflies, fireflies and other beetles, true flies, bees, wasps and other pollinators.  

Fireflies can be very common on vegetation in a yard during the summer months. Scientists view pesticides as a concern for fireflies globally. Photo credit: RachelEllen via FLickr CC.   

References:

  • Bonds, J.A.S. 2012. Ultra-low-volume space sprays in mosquito control: a critical review. Medical and Veterinary Entomology. 26: 121-130. 
  • Oberhauser, K.S., Brinda, S.J., Weaver, S., Moon, R.D., Manweiler, S.A., and N. Read. 2006. Growth and Survival of Monarch Butterflies (Lepidoptera: Danaidae) After Exposure to Permethrin Barrier Treatments. Environ. Entomol. 35(6): 1626-1634.
  • Qualls, W.A., Moser, B.A., Periera, R.M., Xue, R-D, and P.G. Koehler. 2022. Impacts Of Barrier Insecticide Mixtures On Mosquito, Aedes Aegypti And Non-Target Honey Bee, Apis Mellifera.  Journal of the Florida Mosquito Control Association 69: 34-42.

 

 

Caterpillars, In the News, Invasive Species, Tree Insects

Spongy moth: an old pest with a new name

The spongy moth, Lymantria dispar has recently been in the news because of its new name. If you haven’t heard of the “spongy moth” before, it’s probably because you learned of this insect as the “gypsy moth”. It’s the same exact creature, just with a new common name.

Why the change? The word “gypsy” in this insect’s name was originally a reference to persons of Romani descent—“the popular name of the gypsy was no doubt suggested by the brown, tanned kind of color of the male” [Forbush & Fernald, 1896]. In 2021, the Entomological Society of America’s Better Common Names Project started to review the common names used to communicate about insects. Common names that include derogatory or inappropriate terms are being assessed. After a lengthy review process, the term “spongy moth” was ultimately decided upon to describe Lymantria dispar—and fittingly so. The beige egg masses of this insect have a soft, spongy consistency. In French-speaking parts of its range, this species has long been known as La Spongieuse for this very reason. Thus, you’ll be hearing more about the “spongy moth” over time as the term “gypsy moth” is phased out from educational/government websites and other resources.

Spongy moth caterpillar. Photo credit: PJ Liesch, UW Insect Diagnostic Lab

In addition to the name change, the spongy moth should be on our radar for other reasons. Despite being in Wisconsin for decades, this pest can still be a serious defoliator of hardwood trees, both in yards and forested areas. From the period of 2014 – 2020, spongy moths haven’t been much of an issue. An important reason for this is a beneficial fungus known as Entomophaga maimaiga. This fungus was introduced from Japan and it is strongly associated with the spongy moth. Although it took some time to make an impact in the US, this fungus is now viewed as an important “check” on spongy moth populations. Spring rains encourage this fungus, which can cause high mortality amongst spongy moth caterpillars. However, in many parts of Wisconsin we saw an unusually dry year in 2021 which likely curbed the impacts of this fungus. As a result, I saw an increase in cases and reports of spongy moth caterpillars and their damage, adults, and egg masses at the UW Insect Diagnostic Lab last year and Wisconsin also saw a subtle uptick in defoliation of forested areas.

Defoliation (acreage) due to the spongy moth in Wisconsin over time. Source: Wisconsin DNR Forest Health 2021 Annual Report

As illustrated in the chart above, spongy moth populations can be very dynamic and can explode under the right conditions—leading to extensive defoliation. The egg-laying strategy of this species plays an important role in this dynamic. Adult female spongy moths deposit egg masses that can easily contain upwards of 1,000 eggs. In late summer and fall of 2021, I saw plenty of reports where trees contained dozens of egg masses, which could turn into tens of thousands of hungry caterpillars this spring.

Adult female spongy moth depositing eggs. The spongy beige egg mass can easily contain 1,000 or more eggs. Photo credit: Ryan Hodnett via Wikipedia.

Luckily, there’s still a bit of time to take advantage of this knowledge as the young caterpillars typically don’t become active until late April or early May. In the meantime, removal or destruction of the egg masses could help reduce local populations. While often found on trees, the egg masses can also be located on just about any surface in a yard—stacked boards, sides of structures, piles of firewood, and even on vehicles. Don’t delay if you noticed spongy moth activity in your area last year, since it won’t be long before the caterpillars are out and active this spring.

Reference: Forbush, E. H. and C.H. Fernald. 1896. The gypsy moth. Porthetria dispar A report of the work of destroying the insect in the commonwealth of Massachusetts, together with an account of its history and habits both in Massachusetts and Europe.  Boston, Wright & Potter. 495pp.