Month: September 2019

After a good year of plundering crops and fruit and dodging predators and parasitoids, numbers of stink bugs invading homes is on the rise.

This summer witnessed the renaissance of many of our six-legged friends including butterflies and silk moths, but also some nefarious pests like orangestriped oakworm and fall webworm. These were not the only pests on the upswing. Last week stink bugs crashed an outdoor gathering at a friend’s home. Yesterday, at a park in Keedysville, MD, chagrined parents swatted swarms of stink bugs as they collided with children and landed on swings and slides. Over the past two weeks, a deluge of phone calls and emails marked an uptick in reports of brown marmorated stink bugs leering into windows and collecting on siding. The passing of the autumnal equinox marks the beginning of the stink bug’s quest for overwintering refuge and proclaims the start of the home invasion season, a stinky annual tradition throughout much of the country.

They stormed my home climbing walls, finding gaps in screens and siding. They scaled my door frames, ran across my table, partied on my window sills, and probed my walls. The final insult was to lay claim to my coffee cup before my first sip of dark roast.

First discovered near Allentown, PA in the late 1990s, brown marmorated stink bugs (BMSB) now occupy 44 states and four Canadian provinces in North America. Why are stink bugs on the move now? For the past several months, stink bugs have been fattening up on corn, soybeans, garden vegetables, and fruit. But soon this cornucopia of earthly delights will disappear for BMSB and other herbivorous insects. In temperate locations like Maryland, winter halts the growth of deciduous trees and shrubs and withers herbaceous plants. Food for plant and fruit-eating stink bugs all but disappears. With the arrival of cold weather, stink bug movement slows to a crawl and their development grinds to a halt. Prior to this inimical season, stink bugs seek refuge to chill-out where they will be protected from harsh weather and dangerous predators.

Stink bugs preparing to overwinter release aggregation pheromones. This assembly call directs stink bugs to potential hibernal refuges.

Why do stink bugs enter homes and man-made structures? Some folks incorrectly believe these home invasions provide warm winter refuge for stink bugs. Bear in mind that millions of years ago when these creatures evolved, there were no mansions or man-made structures to invade. Until recently, the natural winter redoubts of these stinkers were largely unknown. However, a clever study revealed large, freshly deceased but still standing trees are a prime winter hideout for stink bugs in natural settings. The loose bark of these trees affords a fine location for stink bugs to crawl underneath and escape the ravages of winter. Rocky ridge tops provide many dead trees and abundant places for stink bugs to chill-out. For many viewers of Bug of the Week, stink bugs on rocky ridge tops seems like a remote problem. However, the nuisance potential of BMSB is almost without equal. To a stink bug, a home provides a wonderful assortment of overwintering opportunities beneath siding, behind shutters, and in attics. The pending invasion some homeowners face is no trivial matter. In 2011, a homeowner in western Maryland captured more than 26,000 BMSBs from January through June as they moved about his home seeking egress from their overwintering refuge. Yikes! 

Why do populations of BMSB fluctuate so dramatically from year to year and place to place? Scientists at Virginia Tech and the USDA’s Appalachian Fruit Lab have evidence that visits from polar vortices in the winters of 2014 and 2015 put a beat-down on overwintering BMSB in our region. Fascinating studies at the University of Maryland suggest that our smoking hot summers kill some of the gut microbiota critical to the normal growth and development of stink bug nymphs. Mounting evidence from several universities and government laboratories in our region suggests that indigenous and introduced predators and parasites may be catching up with stink bugs and levying a toll on their populations (see Death of a stink bug, Part 1, Part 2, Part 3, and Part 4).  My money is on the possibility that all of these factors, and perhaps some still unknown, conspired to reduce stink bug numbers in our region over the past several years. However, as is often the case in the natural world, as prey populations decline, so too do numbers of the predators, pathogens, and parasites attacking them. Perhaps a relative dearth of stink bugs in preceding years and a resultant regional decline in Mother Nature’s hit squad has allowed stink bugs populations to rebound a bit this year. Only Mother Nature and the stink bugs know for sure. Is this a crescendo leading to the return of stink bugs to major pest status here in the DMV? Only time will tell. One thing is certain, over the next several weeks stink bugs will be on the move. It’s time to seal cracks and crevices around the home, replace worn weather-stripping and door sweeps, and make sure that screens are in good repair. Steps to keep stink bugs out will also help to keep energy in during the winter season, paying dividends now by reducing the stink bug nuisance and later by saving energy costs.

Acknowledgements

Bug of the Week thanks Marie, Tom, Eloise, Abigail, and members of the BMSB Working Group for providing information and inspiration for this episode. Interesting studies including one by D. B. Inkley, “Characteristics of home invasion by the brown marmorated stink bug (Hemiptera:  Pentatomidae)”, were also consulted. 

To learn more about BMSB biology, distribution and management, please visit the following web site: https://www.stopbmsb.org/  

To learn how to keep BMSB out of your home and what to do when they get in, please watch the following video: Brown Marmorated Stink Bug Control: Keeping Stink Bugs Out of Your House

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A red admiral appears to survey the surrounding landscape from a small branch. Is it seeking a mate or getting ready to search for food?

In a previous episode, we met an electrolyte-seeking red admiral butterfly as it lapped salty perspiration from the back of a hand.  While meeting this butterfly up close and personal was fun, one of the pursuits of typical bug geeks is to observe not only adult insects but also their fascinating and sometimes-cryptic immature stages. The best hope to observe red admiral caterpillars rests on a visit to the moist forest where stinging nettle abounds.  You see, stinging nettles and other members of nettle family, Urticaceae, are favored hosts of red admiral caterpillars.  Having experienced great luck in spotting several red admirals, other brush-footed butterflies, and swallowtails in Shenandoah National Park, a return to nettle covered slopes of the verdant woodland forests seemed like the right move to hunt caterpillars.

After several failed attempts to find a shelter occupied by a red admiral, we hit pay dirt and found a few beautiful caterpillars inside their leafy redoubts. Video credit: M. J. Raupp and P. M. Shrewsbury

This mature red admiral caterpillar will soon form a chrysalis.

On the lower slopes of Hawksbill Mountain stinging nettles abound and red admiral butterflies are easily spotted along the rocky trail. Some caterpillars of butterflies, like those of black swallowtails, are easy to find as they feed in the open on their host plants. However others, like caterpillars of the silver spotted skipper and spicebush swallowtail, have a clever trick to avoid the ever-searching eyes of hungry predators. As they feed, young caterpillars fold and roll individual leaves of their host plant around their bodies, creating an edible shelter. As caterpillars develop and grow, several leaves may be bound together to form a very private and protective “nest.” Pupation also occurs within these leafy shelters.

Whether its extracting salt from a pebbly beach along the Potomac, lapping perspiration from the back of a hand, seeking nutrients from a weep-hole in a tree, or tasting the surface of a lawn chair, red admirals are fascinating to observe.  Video credit: M. J. Raupp and P. M. Shrewsbury

In the waning days of autumn, adults that emerge from pupae will begin a southward journey to warmer realms in Texas and further south to escape the rigors of winter temperatures. When winter releases its grip over much of North America, hibernating adults begin stirring and will soon undertake their journey northward to take advantage of fresh patches of nettles blanketing the forest floor. Two broods of red admirals occur annually throughout much of the United States. Red admirals are not unique to the United States and are found in parts of Central America, Mexico, Canada, several Caribbean Islands, New Zealand, Europe, Northern Africa, and Asia. Last week red admirals were very plentiful in butterfly gardens throughout the DMV, but you better hurry to get a glimpse of these beauties. With the first frost, a speedy exodus of our migrant butterflies to southern latitudes might be just around the corner.

Acknowledgements

Bug of the Week thanks Dr. Shrewsbury for wrangling and videoing red admiral caterpillars. Two superb websites, Butterflies and Moths of North America and Maryland Biodiversity Project, were used to prepare this episode, as was David Wagner’s remarkable Caterpillars of Eastern North America.

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A tiny silvery checkerspot caterpillar glides across the leaf’s surface on delicate strands of silk.

One of the real pleasures of spring is to buy a packet of sunflower seeds, plant them in the soil, and see what develops over the course of the growing season. Having selected a packet marked dwarf sunflowers, we germinated the seeds, grew potted seedlings, and installed them in a front flower bed with expectations of pretty sunflowers just tall enough for close observation at eye-level for children and adults. Little did we know that by the end of August, these sunflowers would exceed ten feet in height, dwarves only for exceedingly large humans or small giants. Fortunately, sunflowers and other members of the aster clan turn out to be excellent hosts for the wonderful silvery checkerspot butterfly, close cousin to the Baltimore checkerspot, state insect of Maryland.

A phalanx of stout spines helps protect the checkerspot caterpillar from the jaws of hungry predators.

The first clues of the checkerspot visit were severely skeletonized leaves. It turns out that the silvery checkerspot female deposits her eggs in large clusters. Upon hatching, tiny caterpillars feed in a great herd on the underside of a leaf, removing the tender tissue and leaving behind only a skeleton of veins and the papery thin epidermal layer of the leaf’s upper surface. By September, several leaves of the sunflower wore the signature of roving bands of caterpillars. Here in Maryland, two broods of silvery checkerspots occur each year, the second of which spends the winter as caterpillars in a protected location on the ground. These caterpillars complete their development the following spring with the return of warm temperatures and the appearance of tender leaves of Jerusalem artichokes, black-eyed Susans and other members of the aster family. Don’t be surprised to see pretty silvery checkerspots nectaring or basking on a wide variety of plants as summer turns to autumn. They can be seen from June through September and have been reported in every county west of the Chesapeake Bay here in Maryland.

Advertised as dwarf sunflowers, these giants soon wore the marks of roving bands of caterpillars as they grazed on leaves and danced in the sunlight. Fully grown caterpillars removed great chunks of foliage before pupating and turning into spectacular butterflies, nectaring and basking in the late summer sun.

Acknowledgements

Bug of the Week thanks Eloise and Abigail for providing inspiration and sharing their caterpillars. Caterpillar guru Karin Burghardt identified the hungry herd and the wonderful Maryland Biodiversity Project website and David Wagner’s “Caterpillars of Eastern North America” were consulted in preparation of this episode.

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A small black spot often with a white center on the inside of each front leg provides a quick clue to separate the European mantis from other species found in our region.

Late summer and early autumn are times when sightings of praying mantises often generate interest from gardeners here in the DMV. It’s not that mantises have spontaneously generated during this season. Rather, these cryptic sit-and-wait predators are pretty tough to spot earlier in the season when they are small and blending in with the foliage of plants on which they hunt. This week an eagle-eyed graduate student spotted a beautiful European mantis hiding in my flower bed.

This European mantis finds brown marmorated stink bugs delicious. Mantises are part of Mother Nature’s hit squad turning back the tide of invasive pests.

The European mantis was first discovered in the US in 1899 in New York State. It arrived apparently as a stowaway on a shipment of nursery stock from Europe. The name ‘mantis’ comes from the ancient Greeks who used the word mantis to describe a soothsayer, or one that could see into the future, and the future of this mantis in the New World has been bright. Since its introduction to North America, this magnificent creature has spread throughout much of the United States. It is now widespread east of the Mississippi and northward into Canada. In years past, European mantises have been invited into our laboratory to enjoy a life devoid of the predators so plentiful outdoors. In captivity our young mantises spend time cavorting in a terrarium and practicing their hunting skills on fruit flies, the mainstay of their diet. As they mature, these predators progress to larger prey such as grasshoppers, caterpillars, and crickets.

This brown egg case, or ootheca, contains scores of eggs that will survive the winter and hatch next spring.

As we learned in a previous episode of Bug of the Week, mantises have a disconcerting habit of eating each other. To prevent unfortunate dining experiences, our mantises are raised in isolation. As summer becomes autumn, our mantises turn their attention towards finding a mate. One particularly lovely femme fatale named Manti enjoyed dinner and a date with a charming, but hapless, and soon headless, gentleman named Little Richard. Manti later presented us with a spectacular egg case called an ootheca. The ootheca is a Styrofoam-like structure deposited by the female mantis on a structure such as a branch or trunk of a tree. A single ootheca may house more than one hundred eggs. Outdoors these eggs endure the inimical winter season safe inside the ootheca, and hatch when warm temperatures and abundant tasty prey return in the spring.

Mantises are not without their own predators. By day, birds hunt these marvelous insects. By night, as mantises fly about seeking food or mates, they are hunted by hungry bats. Bats use ultrasonic signals to detect prey such as moths and mantises in the dark. One might think mantises are helpless in defending themselves from these stealthy nocturnal predators. But mantises have a clever trick up their sleeve or, more correctly stated, a clever ear on their chest. Many species of mantises have evolved an organ to detect sound, an ear so to speak, on the underside of their thorax. Mantises use this ear to detect ultrasonic “chirps” emitted by hunting bats. When the soaring mantis detects the signals of a hungry bat, it evades the bat by quickly diving to the ground.

This morning I happened to spy my resident mantis resting on a milkweed plant enjoying a breakfast of a large milkweed bug. Milkweed bugs bear the orange and black color pattern of other milkweed feeders, including the monarch butterfly, that warn predators of noxious chemicals stored in their bodily tissues. In fact, studies of the Chinese mantid we met in a previous episode demonstrate its ability to learn not to consume nocent milkweed bug prey.  Maybe my European mantis has a more ironclad constitution than its eastern cousin. Or maybe this gastronomic adventure will turn into a dietary mistake. Tomorrow I will check and see if the mantis experienced any digestive distress. As you work in the garden over the next several weeks, keep your eyes open. It’s a good time to catch a glimpse of these beguiling ambush predators.

Hey milkweed bugs, guess who is coming to breakfast. That’s right, a European mantis. And guess what, you’re breakfast! 

Acknowledgements

Bug of the Week thanks Lizzie Dabek for spotting the mantis and providing the inspiration for this episode. The fascinating articles “Recent range expansion of the Praying Mantis, Mantis religiosa Linnaeus (Mantodea: Mantidae),in British Columbia” by Robert Cannings, “The midline metathoracic ear of the praying mantis, Mantis religiosa” by  David D. Yager and Ronald R. Hoy, and “Mantids and milkweed bugs – efficacy of aposematic coloration against invertebrate predators” by May Berenbaum and E. Miliczky, provided keen insights used in this story.

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An explosive season for fall webworms finds trees throughout our region festooned with silken webs.

We’ve had a lot of fun this season enjoying Lepidoptera, members of the moth and butterfly clan, where swallowtails, brush footed butterflies, and silk moths large and small have been featured. In this year of caterpillar glory, several of the not-so-nice moths, including Fall Webworm, have enjoyed a renaissance as well. Actually, the crescendo of Fall Webworm has been building over the past several years and this Bug Guy is hoping they have reached the climax in our region. Fall webworms are causing quite a mess. Complaints about their numbers have been coming in from Baltimore to Washington as they denude trees of leaves and festoon them with their messy, persistent webs.

Eastern tent caterpillars are spring feeders whose tents wind-up in the crotches of branches on preferred hosts like cherry.

 As I visited with folks this summer, several asked about these ubiquitous “tent caterpillars”. Let’s set the record straight: tent caterpillars, webworms, what’s the difference and how do you tell them apart? It’s easy. Eastern Tent Caterpillars (ETC) appear in March and early April in our area and build tents around branches in the crotches where branches diverge, or where limbs join the trunk. The common hosts of ETC are trees in the rose family such as cherry and apple. ETC leave the safety of their nests to feed on foliage along the branches, returning to their nests by evening after eating their fill. They will abandon their nests to pupate on the ground and emerge as adult moths in June and July. By contrast, Fall Webworms first appear in May and June and build expansive nests on the terminals (ends) of branches, incorporating the foliage they will feed upon. A second generation follows the first and in this year of moth and butterfly nirvana, they and their nests are super abundant through July, August, and September.

Inside the webs, fall webworm caterpillars devour leaves and deposit tiny mounds of frass.

Fall Webworms are one of the most catholic of all caterpillars and eat several common trees in our area including cherry, crabapple, maple, sweet gum, sycamore, and walnut. Fall Webworms are known to feed on more than 200 species of plants. Two distinct tribes of Fall Webworms have been described, one with black heads and others with red heads. In the latter half of August, we near the finale of webworm activity for the year. The webworm caterpillars in the nests will soon vacate their shelters to form pupae in the leaf litter and duff beneath trees, where they will spend the autumn, winter, and early spring. Next spring and early summer, adult Fall Webworm moths will emerge from the soil, find mates, and lay hundreds of eggs on the undersides of leaves. Tiny caterpillars hatch and spin small webs, first around their natal leaf and later around small clusters of leaves on the same branch. Inside the relative safety of these webs, larvae munch on leaves. As they grow, larvae enlarge the web to include ever-greater expanses of leaves and branches. When Fall Webworms are abundant, entire trees may be enclosed in these webs. After the first generation of webworms has developed, they move to the ground to pupate, produce new adults, and the cycle repeats. In Maryland, two generations of Fall Webworm are common annually, while in southern states such as Georgia and Texas as many as four generations occur each year.

 In most years and most locations, Fall Webworms do not cause serious damage to trees. However, their nests create a bad case of “ugly” that persists well into the winter. Of course, one easy way to be done with these messy guys is to simply remove them by hand or with pruners when you first see the nests. If nests are far above the ground, a pole pruner may be handy. And don’t just toss the nests aside or you may learn that the caterpillars can march right back up the tree. Place the nest in a bag and discard it. Fortunately for us, Fall Webworm cycles wax and wane in a given area with years of hordes followed by years of few.

A look inside a webworm nest often reveals caterpillars twitching nervously, and why not? A Polistes wasp has landed on the web, extracted a webworm, and turned it into a ball of protein ready for transport back to the nest, food for developing wasp larvae.

Larvae of parasitic wasps emerge from the body of a fall webworm after devouring its internal organs.

More than 50 species of parasitoids and 30 species of predators are known to attack and kill Fall Webworm in North America. People often ask if this is yet another invasive species from another land causing trouble in the US. Nope, this pest is a home grown native that loves our native trees. One issue that really makes me peevish is the ever-increasing influx of exotic and invasive pests we find in our landscapes and gardens. Just think about the misery caused by Japanese beetles, gypsy moths, and emerald ash borer. I am often asked if this is a one-way street, with the USA the recipient of nasty bugs and the rest of the world getting off scot-free. Absolutely not! One of our pesky “gifts” to the rest of the world is Fall Webworm. In the 1940’s this insect was accidentally introduced to Hungary from North America. It has now spread throughout large parts of Europe and Asia. In China, Fall Webworm is known as the North American White Moth and it has become one of the most devastating of all forest pests by damaging thousands of acres of trees each year. Alas, in a world with a global economy we seem destined to share a global biota.  

And that’s not all; deadly assassin bugs like this female wheel bug find fall webworms delectable even while giving a ride to a complacent mate. Yellow jackets also plunder fall webworm tents to bring juicy caterpillars home to feed their young.

Acknowledgements

 Bug of the Week thanks Dr. Shrewsbury for spotting the paper wasp extracting webworms from their nests. ‘Insects that Feed on Trees and Shrubs’ by Warren Johnson and Howard Lyon was used as a reference for this episode.

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