Bane of dogbane, the beautiful and the ugly: Dogbane leaf beetle, Chrysochus auaratus, and dogbane webworm, Saucrobotys futilalis

 

In the meadow, beautiful dogbane leaf beetles can be found dining on leaves of dogbane.

 

In midsummer, meadows abound in wildlife. While visiting a patch of dogbane, I stumbled across two leaf-eaters gobbling leaves of dogbane. One was a real beauty and the other, well, more of a messy beast. The beauty is perhaps the most gorgeous of all insects in the meadow, the dogbane leaf beetle, Chrysochus auratus. The scientific name Chrysochus auratus comes from the Greek and refers to “goldsmith” and “gold.” One look at the fantastic metallic hues of blue, green, gold, and red on the surface of the beetle tells it all. This beetle has no accepted common name, but it is often referred to as the dogbane leaf beetle due to its habit of feeding almost exclusively on plants in the genus Apocynum, herbaceous plants we refer to as dogbane. Dogbane grows along roadsides and trails near the forest edge. It is a perennial with clusters of small white flowers. If you damage a leaf or stem, it oozes a white sticky sap. There in full view, with luck you will find the dogbane leaf beetle. It is a wonder that an insect so conspicuous can survive in a world where birds, toads, and mice dine on insects with gusto.

Ah, but there is a secret to the dogbane beetle. The dogbane plant, like its relative the milkweed we met in a previous episode with its nemesis the milkweed longhorned beetle, is full of highly poisonous compounds known as cardenolides. These compounds are toxic to a variety of animals, including humans. Cardenolides are also known as cardiac glycosides and they can have profound and lethal effects on the heart if ingested. It is likely that these compounds evolved to keep leaf-munching animals from eating dogbane. The clever Chrysochus has the ability to eat the leaves of dogbane unscathed. Instead, it ingests cardiac glycosides, stores them in glands, and then secretes them when threatened by its own predators. It is believed that these toxic compounds confer protection from hungry predators that would otherwise devour Chrysochus. The conspicuous color and tendency for the beetle to feed and rest in full sight of its enemies are probably the beetle's way of advertising its nasty chemical defense. The biological message is this: “That's right, I'm bad, don't even think of eating me.”

When the goop is just too much to handle, a backward stroll helps the dogbane beetle to rid its mouthparts of sticky latex.  

In the ongoing struggle between dogbane and Chrysochus, it looks like the beetle has the upper hand, right? Well, not exactly. Dogbane has yet another trick to foil its herbivores. In addition to nocuous glycosides in their tissues, the sap of dogbane is a sticky, white liquid similar in consistency to latex paint. Insects attempting to eat dogbane soon find their jaws gummed-up with a rapidly hardening gob of goop. The dogbane beetle has a crafty trick to rid itself of this sticky mess. After nibbling for a while, the dogbane beetle does a moon walk while dragging its mouthparts on the leaf to wipe-off the sticky dogbane latex. Once free of the latex, it moves to a new spot to resume its feast.

As they age, dogbane webworms will change color from leaf-blending green to aposematic orange.

In addition to a beautiful beetle, dogbane is attacked by another herbivorous insect which some might consider more on the ugly side. Dogbane webworm is the larval stage of what is known as the panic moth. Young caterpillars of this species are green in color, which help them avoid hungry eyes of predators by blending in with leaves of dogbane. As they grow and their webs enlarge, they assume an orange color with contrasting black spots making them quite conspicuous. In a series of clever studies, Dr. Jacqualine Grant demonstrated that the aposematic orange coloration of dogbane webworms likely served as a warning to predators. Simulated predatory attacks resulted in caterpillars regurgitating gut contents laden with nasty compounds capable of repelling predators. Once again, an herbivorous insect turned the tables on chemically defended dogbane and used dogbane’s noxious chemicals for its own defense.

In addition to beautiful dogbane leaf beetles, patches of dogbane are frequented by tent-making dogbane webworms. As they grow, they become more orange in color to warn predators of their nasty defense, gained from ingesting dogbane’s noxious chemicals. Feeding by these caterpillars puts a beatdown on dogbane plants.

Now is a great time to explore the meadow to enjoy these marvelous beetles and creepy caterpillars and witness the ‘tit for tat’ relationship they have with their chemically defended host.

Acknowledgements

Information for this week’s episode came from “The Love of Insects” by Thomas Eisner, “Deactivation of plant defense: correspondence between insect behavior and secretory canal architecture” by Dave Doussard and Bob Denno, and “Ontogenetic colour change and the evolution of aposematism: a case study in panic moth caterpillars” by Jacqualine B. Grant. We thank Deak and Sheri for sharing their dogbane patch and Master Naturalist students at Nature Forward that provided the inspiration for this episode.

Why am I seeing more spotted lanternflies? Lycorma delicatula

 

In regions infested with spotted lanternflies bright red nymphs (left) are molting into adults (right) ready for mischief.

 

Vegetation beneath trees infested by spotted lanternflies glisten with honeydew excreted by lanternflies as they suck sap from trees.

Last week inquiries poured in regarding hordes of brilliant red insects bespeckled with white spots and black patches aggregating on trees and dashing across lawn furniture and buildings. These are the fourth juvenile feeding stage, a.k.a. nymphal stage, of the despicable spotted lanternfly. In slightly cooler locations in Maryland like Hagerstown and Cumberland the majority of lanternflies were nymphs last week, but in warmer locations like Columbia and College Park youngsters has transitioned to sap-sucking adults. The deluge of honeydew excreted by lanternfly nymphs and adults as they feed has begun, fouling underlying vegetation and attracting stinging insects. The most frequently asked question over the past week or two has been, why are we seeing more lanternflies? At least three reasons help us understand. First, let’s go back a decade to spotted lanternflies’ original detection in Berks County, PA.  In the intervening decade, spotted lanternfly has established and is reproducing in more than a dozen states with some infestations more than 600 miles distant from Berks County. More people are encountering lanternflies simply because they now occupy a much larger geographic area in the US.  

In areas infested with spotted lanternflies, bright red nymphs are molting into adults. In Columbia, Maryland, the deluge of honeydew excreted by lanternflies has begun. Honeydew rains down from trees, forming pools and fouling objects below. Sugar-rich honeydew attracts many types of stinging insects including paper wasps, yellowjackets, European hornets, and honey bees. Get ready for lanternfly showers and be careful around stinging insects.

Second, as lanternflies spread either by natural means or potentially over hundreds of miles with human assistance, new colonies become established. New infestations might be founded by small numbers of undetected egg masses, each with 30 to 60 eggs, that hitched a ride on some lawn furniture or maybe a metal sculpture. For a number of years these few pioneers might be off the radar, undetected, as was the case with the initial introduction of spotted lanternflies in Pennsylvania. With abundant food sources like the invasive tree of heaven, numerous herbaceous and woody plants and low levels of predators, parasites, and pathogens tracking their burgeoning population, lanternfly populations can enjoy a period of exponential growth. As satellite colonies merge along the ever-expanding lanternfly front and as populations rise in the generally infested area, more people encounter spotted lanternflies.   

Since its discovery in Berks County, PA a decade ago, with human assistance the spotted lanternfly has moved more than 600 miles to several states.

Third, bigger insects are more commonly noticed than smaller ones. Tiny lanternfly nymphs hatching from an egg are but a few millimeters long. They scuttle about vegetation on the forest floor and low-lying shrubs feeding on more than a 100 plant species. However, by July, brilliant red nymphs have molted into tawny coated adults an inch or more in length. Being more than 20 times larger than youngsters, they are more readily noticed as they cluster on the trunks of trees or take flight as they move about the landscape in search of food, mates, and places to deposit eggs. In reality, due to high juvenile mortality of nymphs, which is the hallmark of most insect species, there are actually far fewer lanternflies now than there were back in May when eggs first hatched. Readers will certainly find no solace in this.

Sugar-rich honeydew excreted by spotted lanternflies attracts yellow jackets and other stinging insects.

What’s next for spotted lanternfly here in the DMV and around the land? Hordes of adult lanternflies and their attendant deluge of honeydew abound in my neighborhood in Columbia, MD. Underlying vegetation is drenched by sweet sticky honeydew which provides a substrate for sooty mold to grow and soon turn leaves and stems black. The sugar junkies, wasps and bees, have arrived to enjoy the carbohydrate bounty.    

Is there any good news here? As we learned last autumn, scientists at Penn State documented more than 1000 attacks by spiders, mantises, birds, and other predators of spotted lanternflies. Also getting in on the act are naturally occurring soil fungi that have caused at least one lanternfly population to collapse in Pennsylvania. Here’s hoping Mother Nature sends some of this help our way soon.         

Acknowledgements

Thanks to Lisa Robinson and Jennifer Franciotti for providing the inspiration for this episode. Thanks also to Brian Eshenaur and the entire team at the New York State Integrated Pest Management Program of Cornell University for providing the updated maps of spotted lanternfly in the US. The fascinating article “A pair of native fungal pathogens drives decline of a new invasive herbivore” by Eric H. Clifton, Louela A. Castrillo, Andrii Gryganskyi, and Ann E. Hajek was used as a reference for this episode.

Chafer madness: Oriental beetle, Anomala orientalis, and Asiatic garden beetle, Maladera castanea

 

Chafers such as exotic invasive Asian garden beetles (top) and Oriental beetles (bottom) can mean big trouble for your ornamental plants.

 

Three weeks ago, we visited fireflies that are enjoying a spectacular year here in the DMV and in other states in our region. One reason for this renaissance may be due to the benign winter and mild moist spring that may have boosted survival and development of soil-dwelling larval fireflies. Ah, but it appears that in addition to beneficial fireflies, there are other denizens of the soil which also enjoyed conditions favorable for their survival: plant-eating scarab beetles known as chafers.   

Despoiling petals of my coneflowers is just another meal for the Oriental beetle.

Each year, I strive to raise a crop of interesting sunflowers to attract pollinators and birds to photograph and enjoy. However, over the past few weeks, leaves of my sunflowers disappeared in bits and pieces down the gullets of small scarab beetles known as Oriental beetles and Asiatic garden beetles. We met other members of this destructive branch of the scarab clan in previous episodes on Japanese beetles and green June beetles. Oriental beetles are yet another exotic invasive pest introduced to the US sometime before 1920. Originally detected in Connecticut, Oriental beetle now ranges from Maine to the Carolinas and west to the Heartlands. Like Oriental beetles, Asiatic garden beetles are invaders from Asia first detected on the east coast in New Jersey. Their discovery in the Garden State in 1921 followed the earlier discovery of Japanese beetles in 1916. Asiatic garden beetles now range from Canada to Florida and west to the Mississippi. As adults, these scalawags are known to eat more than 100 species of ornamental plants, but they can also be important pests of vegetables, including corn.

The misery these beetles levy on our ornamental plants comes as they munch leaves and flowers of our trees and shrubs. Over the past week or so, great chunks of leaves and flowers vanished seemingly overnight from my sunflowers and butterfly bushes. Repetitive and thorough daytime plant inspections failed to reveal the perpetrators of this assault. However, a midnight’s visit to my butterfly bush revealed hordes of Asiatic garden beetles and Oriental beetles busily stripping away the foliage. Grubs of these little rascals, commonly known as white grubs, have been rooting about in my flower beds and lawn since their mothers deposited eggs in the soil early last summer. During the past year, conditions for survival of white grubs were spectacular. This heralded the possibility that the scarab clan would likely be problematic this year and unfortunately for our plants, the prediction seems to be coming true. By munching roots of grasses, annual, and perennial plants, white grubs can be important pests. Oriental beetle grub counts can approach as many as 60 per square foot of turf in heavy infestations. Here in Maryland by late spring larvae of chafers have completed development, pupated, and adults make their grand appearance in the first half of June. They will be present for the majority of the summer, devouring leaves and punishing blossoms in my landscape beds.

Leaves of my sunflowers have been disappearing over the past few weeks. Daytime inspections revealed nothing but a nocturnal recon nailed the perps, Oriental beetles like the patterned one on the left and brown Asiatic garden beetles like the one on the right. Watch as an Asiatic garden beetle devours a sunflower leaf. The handiwork of these rascals leaves me wondering if my poor sunflowers will bloom at all.

Managing Oriental beetles and other scarabs usually focuses on destruction of grubs in the turf and several products are available. One group of insecticides widely used for controlling white grubs including Japanese beetles and Oriental beetles are the neonicotinoids. These compounds have received much recent attention due to their impacts on pollinators, particularly bees. A fascinating study by Dan Potter and his colleagues at the University of Kentucky revealed that turf treated with the neonicotinoid insecticide clothianidin was not the best place for bumble bees to forage. White clover in plots treated with clothianidin expressed the insecticide in their blossoms, which in turn intoxicated the bees. However, once the clover blossoms had been removed by mowing, the exposure to bees was mitigated. A second white grub-killing insecticide evaluated in the study, chlorantraniliprole, presented no detectable adverse effect for the bumble bees.

Like other species of white grubs, Oriental beetle larvae consume the nutritious roots of plants.

In addition to synthetic insecticides, many folks recommend the use of nematodes to control white grubs in turf. Nematodes enter the grub and release a lethal bacterium. There are many different species and strains of nematodes. Dave Shetlar of the Ohio State University suggests that products containing strains of Steinernema carpocapsae are a bit less effective against beetle grubs than species in the clan named Heterorhabditis. You must wait until late July or August when grubs are in the soil, if you go the nematode route. Several species of parasitic wasps attack white grubs with paralyzing stings and deposit their eggs on the grub. Upon hatching, these parasitic wasp larvae consume their hapless victim. Flowering plants such as goldenrods and bee-balms are magnets for adult wasps, which require nectar and pollen sources. I always have these in my flower beds to attract these highly beneficial wasps, part of Mother Nature’s hit squad that help mitigate pests like white grubs. For me, plucking the beetles from the plants and either crushing their small bodies or giving them a swim in a cup of soapy water provides some retribution for their miscreant behaviors. There may be some good news on the horizon regarding these noisome grubs. Droughty conditions in June and July when female beetles deposit eggs in the soil generally disfavor survival of eggs and young larvae. While summer droughts may not benefit lawns and ornamental plants, they are a pariah to pesky chafers. 

One more thing about Asiatic garden beetle. They are notorious for being attracted to light. I don’t know about you, but part of my regular nighttime routine involves reading a good book at bedtime. During the past few weeks, these moments of mindfulness have been interrupted by a steady pelting of rather large scarab beetles attracted to the light from my bedroom window. So, if you hear something go bump in the night at your bedroom window and if your sunflower’s leaves are disappearing mysteriously, grab a flashlight and have a look for these midnight marauders.

Acknowledgements

Excellent references such as “Assessing Insecticide Hazard to Bumble Bees Foraging on Flowering Weeds in Treated Lawns” by Jonathan L. Larson, Carl T. Redmond, and Daniel A. Potter, “Destructive Turfgrass Insects” by Daniel Potter, and the publication found at the following link were used in preparing this episode:  https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0066375

Always a surprise: European earwig, Forficula auricularia

 

The earwig, my dear, is nothing to fear. Despite what you heard; it won’t climb in your ear. Those pinchers you see at the end of its tail are for picking up groceries, garbage, and mail. From “26 Things that Bug Me” by M.J. Raupp

 

Earwigs almost always surprise me. Whether it’s when I inspect my flowers at night, look behind a tree face on my American elm, or open a hatch on my kayak, there they are, a kind of creepy scrum of wiggly, pincher-tailed insects. Earwigs belong to an order of insects called Dermaptera, derived from the Greek meaning “skin wing”. This derivation refers to the hind wings of the earwig that are not often seen, as they are folded beneath and hidden by the forewings. The common name of earwig is thought to refer to the shape of the hindwing which, when unfolded, resembles a human ear, according to Wikipedia.  An old urban legend has it that earwigs crawl into human ears to lay eggs. While this legend has been largely debunked, there are actually two documented accounts of earwigs entering people’s ears, much to the consternation of the human and presumably the earwig.

Clusters of earwigs are often found on flowers or foliage where they munch blossoms and leaves.

During a recent question and answer interlude following a presentation, one clever listener wanted to know a bit more about earwigs and what roles they played. Well, I can’t speak about all earwigs, but with our common non-native earwig, Forficula auricularia, I do have some relevant experience. Several years ago, I had a wonderful bed full of marigolds with glorious blossoms. Little by little I noticed ever increasing levels of defoliation on the leaves of many plants. I carefully inspected the plants each day to see who the culprit might be. This mysterious mandibulate leaf-muncher remained a mystery until one midnight I crept out to the garden and discovered legions of European earwigs feasting on my marigolds. Undoubtedly, earwigs are herbivores. Several years later while studying misery levied on azaleas by azalea lace bug, one of my students discovered European earwigs snacking on azalea lace bug nymphs. So, clearly European earwigs are omnivores leading a Dr. Jekyll and Mr. Hyde existence as beneficial predators of plant pests and pests in their own right when they eat our ornamental plants and vegetables. These strange insects do have some admirable traits shared even with ourselves. Mother earwigs tend their eggs in an egg nest, cleaning them and moving them about to keep them free of pathogens and in proper ranges of temperature and humidity. Following egg hatch, nymphs are guarded and fed by their mother. 

Earwigs almost always surprise me. Whether it’s a nighttime raid on my flowers, when I peek behind a tree face on my American elm, or when I open a hatch on my kayak, there they are, a kind of creepy scrum of wiggly, pincher-tailed insects.

As alluded to above, earwigs are most active at night and seek dark moist places to hide during daylight hours. Perhaps their most notable and unique attributes are the intimidating pinchers, aka cerci, found at the tips of the earwig’s abdomen. These formidable appendages are used in defense, mating, and prey capture. However, pinches delivered by the cerci tend to be more surprising than painful. In addition to scary pinchers, abdominal glands produce irritating benzoquinones that can be sprayed on attackers while held fast by its pinchers. So, hail the earwig for their beneficial activities as predators, but reserve a modicum of blame for their sneaky nocturnal attacks on plants.

Acknowledgements

Bug of the Week thanks an avid listener to a presentation on climate change who inquired about earwigs and provided the inspiration for this episode. The short communication “Earwig in the ear” by J. R. Fisher, the fact-filled Featured Creature bulletin “Common name: European earwig scientific name: Forficula auricularia Linnaeus (Insecta: Dermaptera: Forficulidae)” by John Capinera, and the wonderful “Secret weapons” by Thomas Eisner, Maria Eisner, and Melody Siegler were used as references for this episode.

Watch out monarda munchers, a wicked wasp is coming to get you: Four-toothed mason wasp, Monobia quadridens

 

When not hunting caterpillars, four-toothed mason wasps can be found pollinating a variety of plants like snow-on-the-mountain.

 

Left unchecked, caterpillars of the raspberry pyrausta wreak havoc on blossoms of bee balm.

Two weeks ago we met the sneaky raspberry pyrausta, a pretty moth whose very hungry caterpillars love to pillage bee balm and other members of the monarda clan. To preserve the nectar rich blossoms of monardas for pollinators, we discussed ways to mitigate injury caused by ravaging caterpillars like removing them by hand or using interventions with OMRI listed insecticides. Well, in my garden last week, good old Mother Nature interceded with another solution to these blossom busters in the form of biological control provided by a nifty wasp known as four-toothed mason wasp.

Recently we saw leaves and buds of bee balm ravaged by caterpillars of the raspberry pyrausta. But this week, Mother Nature sent a member of her caterpillar hit-squad. Watch as the four-toothed mason wasp searches the foliage for a caterpillar. Score! The tiny caterpillar will be stung, paralyzed, and sealed in a brood cell to provide fresh meat for the wasp’s developing youngster.

We met this caterpillar-hunter as a busy pollinator last winter and learned about its dual ecosystem services of pollination and biological control. As adults, mason wasps are often seen visiting flowers, where they provide the important ecosystem service of pollination as they seek nectar to power their hunt for prey and pollen as a protein source to be transformed into eggs.

Mountain mint looks like a super food for mason wasps as they carbo-load in preparation to search for caterpillars. Watch as a female sips nectar from several blossoms before the hunt. Natural holes made in wood by other insects and human-made holes drilled in logs for mason bees make great nurseries for mason wasps. A little tickle with a wisp of wood brings a female out of her nursery. A quick look around reveals nothing amiss and back she goes into the gallery to resume her work. To my surprise, a weep-hole made in the vinyl frame of my living room window makes a great nursery for a mason wasp. After provisioning galleries with paralyzed caterpillars to feed their young, mothers gather balls of mud which will be used to seal the nursery chambers. Using jaws and patience, a female makes a beautiful mudball. With the mudball complete and cradled beneath her legs, she flies back to her nursery. It takes several loads of mud to seal the gallery completely. Here a mother puts the final touches on her handiwork. A solid coat of mud plaster helps prevent enemies from attacking and killing her developing brood.

I discovered these cells containing larvae of mason wasps in a channel of my living room window.

After finding a suitable gallery, which could be the drain hole in a window frame or an unused gallery of a mason bee or carpenter bee, the female mason wasp deposits an egg within the gallery. She then exits the gallery to hunt small caterpillars, many of which are garden pests. Upon encountering a caterpillar, the female mason wasp uses a potent venom to paralyze the prey. Sometimes as many as 19 caterpillars are captured, paralyzed, and used to provision the cell where an egg awaits. Ah, but these caterpillars are not truly dead. Like Westley, the Dread Pirate Roberts of Princess Bride fame, these caterpillars are only mostly dead. Paralyzed but still living, they provide fresh meat to be consumed after the spawn of the female wasp hatches from an egg deposited in small cell within the gallery. Upon hatching, the wasp larva drops onto the hapless caterpillar to feast.

When a sufficient number of prey have been captured, the female seals the gallery with a plug of mud or sand particles, hence the name mason wasp. In a remarkable display of gender control, the female wasp is able to lay either a male or a female egg. Due to the shorter developmental time of the male offspring, male eggs are usually placed near the opening of the gallery and female eggs are placed deeper within. If you see these magnificent black and white wasps entering drain holes on your window frames, fear not, your home is not under attack. You have provided a nesting site for these black and white beauties. In return, they will pollinate your plants and help eliminate pests like the caterpillars on monardas and other garden plants.

Acknowledgements

The wonderful references “Trap nesting wasps and bees: Life histories, nests, and associates” by Karl Krombein and “The cocooning habit of the wasp, Monobia quadridens” by Phil Rau were consulted to prepare this episode.