Month: August 2025

What’s not to like about lady beetles, right? Cute, sometimes brightly colored beetles helping to rid our gardens and landscapes of pests like crape myrtle bark scales and aphids. Well, sometimes they do invade our homes. But like many large families, part of the clan sometimes goes astray and lady beetles in the genus Epilachna evolved to eat plants rather than other insects.

The aboriginal home of the Mexican bean beetle is the high southern plateau of Mexico where many members of the bean plant family grow. As beans became widely cultivated in the United States, the Mexican bean beetle crossed the border and spread throughout the eastern half of the US where moist conditions and many types of cultivated beans favor its survival. In some years, Mexican bean beetles are relatively scarce due to depredations of a small parasitic wasp, Pediobius faveolatus, released decades ago in the mid-Atlantic region. However, in a local community garden, this year’s wet spring and warm summer seem to have provided the perfect growing conditions for the bean beetle.

A recent visit to the community garden revealed all sorts of beans in sad shape. This saga began back in spring when female Mexican bean beetles deposited scads of bright yellow eggs on undersides of bean leaves. From the eggs hatched spiny bright yellow larvae that scraped the epidermis from the leaf surface creating damage called etching. As larvae grew, their strong jaws chewed holes in the leaves. When larval development was completed, they formed pupae which dangled beneath bean leaves. From these pupae hungry adult beetles emerged and continued the impressive defoliation of the beans. One fool proof way to help reduce populations of beetles is to remove adults, larvae, and eggs from the beans when you find them. 

As I meandered through the garden plots, almost every leaf of snap and lima beans was skeletonized by the feeding of the larvae and adults of this mini-jawed monster. Bristly, bright yellow larvae fed alone or in groups of 2 or 3. Orange and yellow adults with black spots scraped and munched the green tissue between the tougher veins of bean leaves. This nutritious food is converted into eggs and each female can produce as many as 600 eggs during the course of her lifetime. Laid by dozens, these bright yellow eggs hatch in about a week. Larvae complete development and form pupae, which hang suspended from the leaves of bean plants. As summer wanes, adult beetles seek shelter in decaying vegetation or leaf litter to survive the chill of winter. In spring, adults emerge from their refuge and move back to the bean fields to resume feeding and producing pestiferous spawn.

One way to reduce problems caused by these hungry bean-eaters is to remove plant refuse from the garden plot at the end of the growing season. Refuse relocation forces overwintering beetles to take a longer and more perilous journey to the garden from hibernal refuges. Some gardeners use floating row covers with a fine mesh to prevent beetles from reaching the bean leaves. These should be put in place early and kept in good repair. Another strategy to confound this pest is to plant a small “trap crop” of a favored food like snap beans in the garden early in the season. This early plot will attract and collect overwintering beetles as they emerge from their refuges. Once the beetles have moved in, the trap is set, and by annihilating the trap crop loaded with beetles, the number of beetles remaining to attack beans planted later in the growing season will be reduced.

 

Another method of control is a bit more direct and involves crushing eggs, larvae, and adults on the plants. Seems foolproof but be forewarned that fingers may turn orange after encountering defensive secretions produced by the beetles. And if you go the crushing route, please avoid the urge to lick your fingers, as the defensive secretions produced by the larvae and adults are a witches’ brew of noxious alkaloidal compounds that ward-off would-be predators. If you want to go the biological control route, the parasitic wasp Pediobius faveolatus may be available from commercial suppliers and released in your garden but be sure to follow directions as timing is critical for this method of intervention. While it may be a little late to save the beans this season, make a note of the health of your beans this year and consider your options for next year. Remember, beans are good.                    

References

 Information used in preparing this Bug of the Week came from the marvelous article “The chemistry of phyletic dominance” by J. Meinwald and T. Eisner. Bug of the Week thanks community gardener Barbara for demonstrating the value of row covers.

More information on Mexican bean beetle and its management can be found at the following website: https://extension.umd.edu/resource/mexican-bean-beetle-vegetables/

 

 

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There is no mistaking this caterpillar on a boxwood. This is the larva of the box tree moth. Paula Shrewsbury image

From the time of our earliest European colonists, boxwoods have been important components of ornamental landscapes. Boxwoods grace iconic landscapes in the DMV including George Washington’s home at Mount Vernon, the “Box Walk” at  Dumbarton Oaks,  the National Boxwood Collection at the United States National Arboretum, as well as hundreds of public and private gardens and landscapes in our region. However, boxwoods are one of the most problem-prone plants in our landscapes. Already beset by exotic pests including leafminers, spider mites, and pathogens such as boxwood blight, boxwoods in the DMV and throughout our country now face a new, lethal non-native invader, the box tree moth.  Like many of our new invaders box tree moth is native to Asia in China, Japan, and Korea. Probably due to the movement of ornamental plants, it entered Europe and was first discovered in Germany in 2007. It now occupies more than 30 Eurasian countries. It jumped across the Atlantic to Canada where it was detected in 2018 and arrived in the United States with shipments of nursery plants from Canada in 2020 and 2021. Prior to July, 2025 it spread to Delaware, Massachusetts, Michigan, Ohio, Pennsylvania, West Virginia, and New York. Yes, the DMV was surrounded and sure enough, it was detected in Clarke and Loudoun Counties in Virginia and three locations in Washington County in Maryland during the latter half of July and early August.

Iconic boxwoods are one of the most widely planted shrubs throughout the country and here in the DMV. Beset by pests like leafminers, spider mites, and boxwood blight, they now have a devastating new enemy, the box tree moth. Caterpillars of box tree moth defoliated these once handsome boxwoods. The shrubs will be destroyed in hopes of slowing the spread of the moth. Watch as hordes of caterpillars consume foliage until only midveins and silken webs laced with nasty frass remain. In addition to destroying the boxwoods, these miserable leaf-munchers will sometimes eat each other. If your boxwood looks like this, and you see these, please contact your state department of agriculture or university extension service.

What’s the worry? If undetected, an infested boxwood can support a rapidly expanding population of leaf-eating caterpillars capable of completely defoliating large boxwoods. In addition, they create large silken webs littered with frass that accumulates on plants and on surfaces below.

How is this possible? Adult boxwood tree moths lay multiple clutches of 5 to 20 eggs. Larvae that hatch from the eggs are voracious herbivores that first remove green leaf tissue as youngsters and later consume entire leaves. And if this was not bad enough, after leaves are consumed, they feed on woody tissues thereby girdling stems and branches, hastening boxwood death. One generation of this carnage is bad enough, but box tree moth will have many generations in the DMV. In other locations, as many as 4 or 5  generations may occur annually depending on temperature regimes.

What should you look for? Discoloration, a change in the color of leaves from vibrant green to dull brown or gray and defoliation, the loss of parts or entire leaves are often the first and most easily recognizable clues that your boxwoods may be infested with box tree moth. Since no native moth or butterfly has caterpillars that readily eat leaves of boxwoods, the presence of large numbers of strikingly colored black, green, and yellow striped caterpillars with black heads is a dead giveaway for the presence of box tree moths. However, several other arthropod pests and diseases can cause discoloration, defoliation, and dieback on boxwoods. Fortunately, Joe Boggs of The Ohio State University has complied a wonderful pictorial guide to diagnosing boxwood pests and diseases including symptoms and signs of box tree moth.

Defoliated leaves covered with silk and hordes of caterpillars decked out in stripes and spots of green, yellow, white, and black with shiny jet-black heads mark an infestation of box tree moth caterpillars. Paula Shrewsbury image

What should you do if you find box tree moth? The Maryland Department of Agriculture is presently engaged in a program to limit the spread of box tree moth. If you suspect you have this pest, the Department of Agriculture recommends the following:

·         If you suspect your boxwoods may be infested with the box tree moth, please contact via email the Plant Protection and Weed Management program at [email protected]. Please attach a picture in your email.

·         Allow Maryland or Federal agricultural officials to inspect your boxwood plants and place detection traps.

·         Any infested material should be doubled bagged in plastic bags and placed in the trash.

·         Nursery owners should monitor their boxwoods and implement safeguards to limit pest risk. All licensed nurseries should report BTM detections to the Maryland Dept of Agriculture Nursery Inspection Program or reach out to their nursery inspector.

Moving forward, what might the future hold for the box tree moth and us? Unfortunately, like emerald ash borers, brown marmorated stink bugs, spotted lanternflies and many other non-native pests of our landscape plants, the box tree moth is likely here to stay. However, Mother Nature in cooperation with humans often has a solution for these invaders. Indigenous natural enemies, predators, parasitoids, and pathogens often rally and put a beat-down on these non-native pests. Clever scientists search and discover natural enemies from afar and after exhaustive evaluation release them to reduce populations of invaders here in the US. Researchers develop chemicals to detect, attract, trap, and kill non-native pests. Even today several insecticides are available to kill caterpillars. Some of these contain active ingredients like Bacillus thuringiensis, a.k.a. BT, and spinosad which are dynamite for controlling caterpillars but safe enough to be used in organic food production.  If you want to learn more about insecticides that can be used to manage box tree moth caterpillars, click on this link. With diligence, ingenuity, good science, and help from Mother Nature, we will find ways to manage this new  noxious invader.  

Box tree moth caterpillars can destroy an established stand of boxwoods like this one in a matter of weeks. Joe Boggs, OSU.

References and acknowledgements

“The fast invasion of Europe by the box tree moth: an additional example coupling multiple introduction events, bridgehead effects and admixture events” by Audrey Bras, Eric Lombaert, Marc Kenis, Hongmei Li, Alexis Bernard, Jérôme Rousselet, Alain Roques, and Marie‑Anne Auger‑Rozenberg was used as a reference for this episode. We thank Joe Boggs for generously allowing us to use his wonderful images of box tree moth. The inspiration for this episode came from Phyllis and Rod who allowed us to photograph their boxwoods and caterpillars.  Please visit Box Tree Moth by Madeline Potter to learn more about this pest and explore links to additional information.

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Five years ago in an episode entitled “Missing bugs of the week: Swallowtail butterflies, Papilionidae” we explored some of the reasons pollinators in general and butterflies in particular are imperiled in the DMV and around the world. Last month a concerned nature enthusiast remarked “normally by this time of the year our meadow would be full of butterflies… even a monarch or two…. This year there’s virtually none and I hear it’s that way throughout the county.” In a sample size of one, in my own flower garden in Columbia, MD, thus far this season it has been a rotten one for large butterflies like swallowtails and monarchs that usually are plentiful by now.  My barometer for gauging butterfly abundance is a large native composite known as cup plant (Silphium perfoliatum). In years past during the last weeks of July and first weeks of August, I have seen more than a dozen swallowtails simultaneously enjoying nectar treats on my cup plant. To date only a single tiger swallowtail has visited my cup plant. How disappointing is that?  

Over the last few weeks, folks expressed concern over the absence of swallowtail butterflies in their gardens and meadows. I’ve had the same impression. This video from 2019 shows dozens of tiger swallowtails visiting my cup plant in late July. Fast forward to the same time this year when only a single tiger swallowtail has stopped by. Is this just annual variation in weather conditions or signs of larger issues related to climate change, development, and other sources of butterfly decline? Maybe missing butterflies is just a local suburban thing. Earlier this year on the banks of the Potomac, zebra swallowtails, tiger swallowtails, and other swallowtail species were common gathering minerals from the mud. And in my gardens skippers and cabbage butterflies showed up in force right on time. I’m not really sure what’s up with the swallowtails but I hope a second generation of swallowtails and maybe some monarchs make an appearance soon.

How are butterflies fairing around the country? A recent article in the Proceedings of the National Academy of Sciences  provides some clues as to why butterflies and other pollinators are becoming harder to see and why they may be declining in the United States and Canada. Tara Cornelisse and 14 colleagues found that roughly 26% of vertebrate and invertebrate pollinators are at risk of extinction in North America north of Mexico. When it comes to butterflies, of the 632 butterfly species studied, almost 20% are at risk of extinction. Of these approximately 8% of charismatic swallowtails are at risk. Yikes!

What are the underlying ecological threats to pollinators in general and butterflies specifically? We have known for decades that changes in land use patterns associated with urbanization around the world are responsible for dramatic losses of several insect species, including butterflies. In addition to urban development, the study by Cornelisse et al. ranked climate change, invasive species, changes in the natural patterns of water movement and storage, and changes in wildfire regimes as key risk factors for butterflies and moths. On a national level pollution also imperiled all pollinators in several eastern states.   

Findings of this study send a warning regarding the overall fate of pollinators in our rapidly changing world. However, declines in the abundance of butterflies from one year to the next are often linked to more immediate ecological events such as annual variation in weather. Elevated temperatures are known to reduce the survival of caterpillars. Drought is known to reduce the abundance and nutritional quality of some plants. One butterfly expert suggested that last summer’s extended heat and drought may have negatively affected the survival of butterfly larvae, thereby reducing the populations of butterflies in 2025. Perhaps, our unusually soggy spring weather favored pathogens lethal to butterfly larvae or pupae.

Should we fear that the apparent scarcity of swallowtails in 2025 in my garden in Columbia portends a pending butterfly apocalypse? Maybe not. Beyond swallowtails, other species of butterflies like silver spotted skippers and their kin arrived in my garden right on schedule in fine numbers, as did cabbage butterflies. Recent adventures along the C & O Canal this spring and summer revealed several species of butterflies including tiger and zebra swallowtails in good numbers. Rick Borchelt’s butterfly surveys in Allegany and Kent Counties in Maryland revealed solid numbers of dozens of butterfly species. But as I finish writing this episode and look out the window to the cup plant, swallowtails are still absent. However, hope springs eternal in the hearts of bug geeks and maybe an upcoming brood of swallowtails and some late-to-arrive monarchs will stop by garden my before the summer ends.

Acknowledgements

Bug of the Week thanks Paul Bade for his interest in swallowtails that provided the inspiration for this episode. Science writer, butterfly guru, and keeper of the LepLog Rick Borchelt provided great insights and observations of butterflies throughout the region. Many thanks to colleagues in the Department of Entomology, especially Karin Burghardt and Leo Shapiro for providing references and helping clarify several points discussed in this episode. The following fascinating papers were consulted: “Live fast, die young? Day- and night-warming affect the growth, survivorship, and behavior of caterpillars in the field” by Louie H. Yang, Elizabeth G. Postema, Heran Arefaine, Fernanda Y. Cohoon, Emma A. Deen, Yvonne L. Durand, Gwendolyn I. Erdosh, Hailey Ma, Courtney N. Mausling, Sarah Solís, and Madeline R. Wilson,   “Western Monarch Population Plummets: Status, Probable Causes, and Recommended Conservation Actions” by Emma M. Pelton, Cheryl B. Schultz, Sarina J. Jepsen, Scott Hoffman Black and Elizabeth E. Crone; “Multiscale seasonal factors drive the size of winter monarch colonies” by Sarah P. Saunders, Leslie Ries, Naresh Neupane, M. Isabel Ramírez, Eligio García-Serrano, Eduardo Rendón-Salinas, and Elise F. Zipkina; “Declines and Resilience of Communities of Leaf Chewing Insects on Missouri Oaks Following Spring Frost and Summer Drought” by Robert J. Marquis, John T. Lill, Rebecca E. Forkner, Josiane Le Corff, John M. Landosky and James B. Whitfield; and “Elevated extinction risk in over one-fifth of native North American pollinators” by Tara Cornelisse, David W. Inouye, Rebecca E. Irwin, Sarina Jepsen, Jonathan R. Mawdsley, Margaret Ormes, Jaret Daniels, Diane M. Debinski, Terry Griswold, John Klymko , Michael C. Orr, Leif Richardson, Nicole Sears, Dale Schweitzer, and Bruce E. Young.

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One of my favorite mythological tales is that of King Midas, the ruler of Phrygia who wished for and was granted the power to turn everything he touched into gold. Apparently, this was his undoing as he starved to death when the food he touched turned into inedible gold – poor guy. Last week my nature- loving neighbor shared a wonderful video of majestic mydas flies cavorting around the stump of an ancient pin oak tree that once graced her yard. It seems this stump serves as a perennial home for her mydas flies. Each summer they provide entertaining performances as males battle each other and find romance with the females which, in turn, search for places to deposit their spawn in just the right spot in the decaying stump. Female mydas flies deposit eggs in rotting wood where their predaceous larvae dine on other soft bodied insects, including the grubs of scarab beetles, kin of the ones we met in previous episodes such as “Hercules Beetles.”

The star of this episode, Mydas clavatus, the clubbed mydas fly, named for its clubbed antennae, is a member of a relatively small family of very large flies whose biology remains somewhat unknown. Mydas clavatus is among the largest of all North American flies, with a body length often more than an inch. It is believed that their black–velvet coloration presents the visage of a large stinging wasp. This confers protection from enlightened predators that have learned not to mess with painful, black, stinging insects. One report holds that they also have a behavioral mimicry in which they curl their abdomen and jab at an aggressor in a mock stinging charade aimed to fool potential predators.

Decaying stumps like this one serve as a home for scarab grubs, a critical food source for mydas fly larvae. Watch as a mydas fly searches the base of the stump. Maybe it’s a female looking for just the right spot to deposit her eggs. Nearby on leaves of a holly a mydas fly does a little fly dance with its forelegs.  And on a lilac near the stump another mydas fly shows no fear of a bug geek with a camera. Video credits to Pam Gealy and Michael Raupp

Adult flies have been observed dining on the nectar and pollen of flowers of Spiraea alba, Pycnanthemum virginianum, Asclepias syriaca, A. verticillata, Monarda punctata, Teucrium canadense, Verbena hastata and Saponana officinali. In years past, they frequented by garden, attracted perhaps by the abundance of butterfly weed in my flower bed which served as a beacon for this unusual visitor.

Adult mydas flies are rather tranquil and allow bug geeks to take pictures before flying away for some unknown fly business. Unfortunately for me, the mydas fly that have visited my garden for photo ops lacked the Midas touch and the holly and pumpkin on which it perched failed to turn to gold. Still, seeing these unusual creatures always provides a golden moment for a bug geek.

References

Bug of the Week thanks Pam Gealey for sharing videos and images of her majestic mydas flies that inspired with episode. Dr. Shrewsbury captured images of the mydas fly. The delightful account “Adult female Mydas clavatus (Diptera: Mydidae) feeding on flowers in Wisconsin” by Andrew H. Williams and the interesting web page “Mydas fly” by Jeffrey K. Barnes were used as references.

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