Underway: doomed flights of spotted lanternflies in the DMV - Spotted lanternflies, Lycorma delicatula

 

Dispersal flights by spotted lanternflies are underway. In the human-built environment many spotted lanternflies will fail to reach suitable host plants and will perish like this one, crushed on a sidewalk.

 

Near a grove of heavily infested Tree of Heaven, a short flight into a forest brings a spotted lanternfly to a new host tree suitable for growth and reproduction.

On a stiflingly hot afternoon last week in the parking lot of a large suburban mall, I was treated to a remarkable and somewhat macabre phenomenon playing out in a dozen states in the eastern half of the US where spotted lanternflies engage in their annual dispersal flights. Scientists in the invaded range here in the US and in the native range in Asia have long observed the late summer peregrinations of spotted lanternflies as they take wing on hot summer days. Flights which may cover hundreds of yards are thought to carry legions of unmated female lanternflies to new host trees where they will mate, feed and develop eggs, prior to depositing eggs of the next generation. In the natural world, one full of delectable, nutritious host plants including a favored host, the invasive Tree of Heaven (Ailanthus altissima), taking a short flight to find a high-quality source of food for you and your offspring sounds like a fine idea. Furthermore, if hungry predators like mantises and assassin bugs or parasitic wasps have discovered you and your gang on your natal tree, getting out of Dodge and finding a new tree on which to procreate makes a lot of sense.

But what happens in an unnatural world, the human-built world where a mile of asphalt separates you from the nearest Tree of Heaven one of your preferred hosts for dining and developing? Here’s what I saw. At a shopping mall complex, scores of lanternflies apparently mistook large vertical surfaces of buildings lining the parking lots as hospitable places to land after departing their birth trees, which lined the perimeter of the asphalt desert. One fetching brown wall of a department store seemed to attract an overabundance of lanternflies, which roamed the bark-like cement surface apparently looking for a place to insert a beak. Lacking vascular tissues on which spotted lanternflies feed, these walls were a particularly bad choice to settle in for a meal. For them, starvation was just around the corner. Less fortunate lanternflies crashed into clear plate glass windows or concrete panels and fell onto sidewalks where busy parents buying back-to-school supplies brought a quick end to their puny lives. One eagle-eyed shopper exiting a store spotted a hapless lanternfly on the ground, exclaimed “oh, that’s a lanternfly, we’re supposed to squash them”, and proceeded to do so with a quick two-step. Another lady emerged from a car with two teenagers on their way to see a movie. A wayward lanternfly landed on her son. The mother grabbed the lanternfly, which displayed its gorgeous hindwings, and said “oh, look how pretty this is, I can’t hurt you.” She launched the insect back into the sky. This fascinating contrast reflects societies’ approach to lanternflies, other invasive insects, and sometimes insects in general. Some love them, some despise them, and many are somewhere in the middle.

Spotted lanternflies are on the wing to find new host plants, bringing them in contact with the human-built world where they will wander buildings and benches in search of food. Many will perish of starvation or dehydration on sidewalks and in parking lots. Others will be squashed beneath feet and automobile tires. Some may visit shoppers and diners briefly before flying off, while others will be snared and killed by urban spiders. Before you leave a parking area infested with lanternflies, inspect your car to make sure these clever vagabonds are not hitching a ride with you.

Excepting some form of divine intervention, spotted lanternflies have likely become unwanted but permanent residents in our country. In 2017 during the early stages of the lanternfly onslaught, we reported that more than a million lanternflies had been killed by volunteers in Berks and surrounding counties in Pennsylvania. Despite these herculean efforts, in the intervening five years, lanternflies have spread and established breeding populations in a dozen states, more than eighty counties, and have been detected almost five hundred miles from the place of their initial detection. Here in Maryland, we jumped from 2 infested counties in September of 2020 to 14 infested counties in August of 2022. Lanternflies are on the move.

 

This map charts the distribution of spotted lanternflies in the United States in September of 2020. Credit: New York State IPM.

  

The most recent map of the distribution of spotted lanternfly in the United States in August of 2022 shows a remarkable increase in the number of infested states and counties. Credit: New York State IPM.

 

Despite what you might have heard on television or read somewhere, squashing a few lanternflies in a parking lot in Maryland is unlikely to reduce the abundance of this pest. The vast majority of lanternflies you encounter outside a department store are doomed. In the wild, a diverse complement of predators and pathogens, part of Mother Nature’s hit squad, are already waging war on spotted lanternflies. These beneficial organisms have played important roles in putting a beat-down on other invasive pests like the brown marmorated stink bug. Remember that pest and how things have changed in the last two decades here in the DMV? In addition, clever scientists of the USDA are evaluating enemies of the lanternfly from the lanternfly’s native range in Asia. If these beneficial insects clear rigorous hurdles and pose no threat to our indigenous fauna, they will be released to join the battle against lanternflies. 

What should you do if you spot a spotted lanternfly when you stop in a parking lot in Maryland while on a trip to Colorado? Be sure to carefully inspect your vehicle both inside and out to avoid transporting a stowaway to a new location. If you are simply stopping for groceries before heading home and you live in a generally infested county, squashing a lanternfly may save the doomed lanternfly from a miserable death by starvation or being run over by a car. If you live in a county or location where spotted lanternfly is not known to infest and reproduce, like the District of Columbia or Napa County, California, and think you found a spotted lanternfly, by all means squash it and bring a swift end to its dastardly life, but don’t just toss it out. Please, take a photo of it, place it in a zip-lock bag and send it or the image to your local department of agriculture or nearest university extension service for identification. We need to know what new locations this rascal has invaded to make sound management decisions. Maybe you can be the one to help stop this crafty hitch-hiker from setting up shop in your hometown at least for the time being.

Acknowledgements     

We thank several shoppers and movie-goes in Hagerstown, Maryland for providing inspiration and video footage used in preparation of this episode. The great article “Flight Dispersal Capabilities of Female Spotted Lanternflies (Lycorma delicatula) Related to Size and Mating Status” by Michael S. Wolfin, Muhammad Binyameen,  Yanchen Wang, Julie M. Urban, Dana C. Roberts, and Thomas C. Baker provided information on dispersal behaviors of lanternflies. Thanks 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 distribution in the US.

To learn more about USDA’s efforts to discover beneficial insects with potential to reduce populations of spotted lanternflies, check out this website: https://www.ars.usda.gov/research/publications/publication/?seqNo115=338695

To learn more about hitch-hiking spotted lanternflies, please visit this episode of Bug of the Week: https://bugoftheweek.com/?offset=1600693536810&reversePaginate=true

To learn more about spotted lanternfly flights, please click on this link: https://www.psu.edu/news/impact/story/spotted-lanternfly-collective-flights-late-summer-not-dangerous-public/

To see spotted lanternflies in flight, please click this link: https://www.youtube.com/watch?v=7MqmWHodMN8

To hear a recent broadcast about spotted lanternflies in the DMV on public radio, please click this link: https://www.wypr.org/show/on-the-record/2022-08-25/the-invasive-spotted-lanternfly-and-park-students-in-the-arctic

The other monarch caterpillar: Milkweed tussock moth, Euchaetes egle

 

Hairy caterpillars of the milkweed tussock moth resembling “Cousin Itt” are busy consuming leaves of milkweeds. Image credit: Sam Taylor

 

No mistaking the rather naked monarch caterpillar for its dining partner on milkweeds, the milkweed tussock moth.

Last week my neighbor sent a fine image of a caterpillar resembling Cousin Itt of Addam’s Family fame. The shaggy caterpillar was comically cloaked in black, orange, and white tufts of hair. Hordes of these leaf-munchers have been discovered feeding on milkweed leaves over the last few weeks. With gardeners from coast to coast striving to help our imperiled monarch butterflies find food for their young by planting more milkweed plants, how concerned should we be about these gregarious interlopers horning-in on food for monarch caterpillars? Who are they and what should we do? These caterpillars are the offspring of a species of moth known as milkweed tussock moth or milkweed tiger moth. Before we rage on these rascals, let’s have a little course in milkweed plant and milkweed caterpillar biology.

Milkweed gets its name from the sticky white sap exuded from stems and leaves when their surface is broken by hungry insects or curious humans. Milky sap and cells within the leaves contain nasty chemicals called cardiac glycosides. As the name implies, these compounds have something to do with the heart. At higher concentrations, cardiac glycosides can be heart poisons, bringing death to humans and other animals foolish enough to eat them. However, many insects that eat milkweeds have evolved mechanisms to deal with these toxins and have the ability to consume leaves of milkweed without being poisoned. In fact, they obtain cardiac glycosides from their food and store these noxious compounds in their bodies. Caterpillars of both the monarch butterfly and milkweed tiger moth obtain cardiac glycosides and retain them as they develop into a butterfly or moth, respectively.

Milkweed tussock moth caterpillars devour leaves of milkweeds. Orange and black coloration warns predators not to mess with them.

What is all of this chemical chicanery about? Birds are important predators of many kinds of insects, including caterpillars and butterflies. Scientists discovered that cardiac glycosides found in monarch butterflies caused predators such as blue jays to vomit dramatically following an attempted monarch meal. Blue jays exposed to monarchs soon learned to recognize the monarch by sight and avoided eating these beautiful, but nasty tasting butterflies. Many of the insects that live on milkweed and consume its leaves display vivid patterns of orange and black as both juveniles and adults. This convergence on a similar, easily recognizable color pattern by two or more nasty-tasting insects is called Müllerian mimicry. Other milkweed feeders that participate in the milkweed mimicry ring include milkweed longhorned beetles, milkweed bugs, and milkweed leaf beetles we met in previous episodes. Like the larvae of the monarch, caterpillars of the milkweed tiger moth obtain cardiac glycosides from milkweeds and retain them as adults.

Adult milkweed tussock moths have drab brown wings but a pretty racy abdomen sporting Halloween colors of orange and black.

While the caterpillars of this tiger moth boldly wear the characteristic warning colors of orange and black as they feed during the day, the adult moth is comparatively drab at first glance with pale brown wings, but its impressive abdomen sports Halloween colors of orange and black. The fact that caterpillars of the milkweed tiger moth store cardiac glycosides for use as adults is somewhat perplexing. Primary predators of these night-flying moths are fearsome bats that hunt using sound rather than sight to locate prey. Orange and black coloration may have little value in defeating these night-hunting predators. However, the cardiac glycosides stored in the body of the moth are put to good use. The resourceful milkweed tiger moth evolved an organ that emits an ultrasonic signal easily detected by bats. The signal warns that an attack will be rewarded with a noxious distasteful meal and bats soon learn to avoid the tiger moth as prey. 

What can you do to preserve your milkweeds as a food for monarchs? Well, you really don’t want to reach for pesticides to do away with any leaf-eaters that may have come to dine on your milkweed. Although we endeavor to help our monarchs, remember that these tussock moths are an important part of our natural ecosystems too. They have their own complement of predators and parasites that depend on them as a source of food. If you are trying to enjoy monarchs dining on the milkweed patch in your garden or landscape, perhaps the best strategy is to simply collect your tussock moth caterpillars in a container and relocate them to the nearest patch of milkweeds in a nearby meadow.

Acknowledgements

Bug of the Week thanks Randy Taylor, Sam Taylor, Chris Sargent, and several Bug of the week viewers for providing the inspiration for this week’s episode. Two delightful references  “Sound strategy: acoustic aposematism in the bat–tiger moth arms race” by  Nickolay I. Hristov and William E. Conner and “Secret Weapons” by Thomas Eisner, Maria Eisner, and Melody Siegler provided valuable insights into the mysterious ways of this week’s stars.

Weeding can turn spicy when saddlebacks are around: Saddleback caterpillar, Acharia stimulae

 

Front, rear, and along the flanks, venom glands in the skin of the caterpillar prepare a potent venom delivered via urticating hairs.

 

Last week ago, while mowing the lawn, I felt a familiar stinging sensation on my left calf after brushing up against some plants at the border of a flower bed. This surely felt like the burning pain associated with the sting of a caterpillar, but a cursory inspection of the vegetation failed to reveal a suspect. Fast forward to this week when, while pulling weeds in the same flower bed, I was treated to several stings on my lower and upper arm. This time the culprit was easy to spot resting on an iris frond where I had apparently interrupted its lunch. One’s first encounter with the saddleback caterpillar is usually memorable, more likely to be experienced through the sense of touch rather than the sense of sight.  

While weeding a flower bed, a saddleback caterpillar taught me a memorable lesson: don’t mess with a caterpillar armed with venomous spines. Watch as the saddleback defends its flanks from attack by a dissecting probe. First it turns left and engages the probe with large spines located on fleshy protuberances called scoli, found near the head and the tail. A gentle poke on the right side produces a similar defense. BTW, following this harassment, the saddleback shuffled down the leaf and resumed its meal unharmed.

Adult saddleback moths are rather nondescript rascals commonly seen in summer and autumn in the DMV (male above, female below).

Protecting the front and rear flanks of the garishly beautiful caterpillar are projections festooned with nasty spines. Like the stinging spines borne by the larvae of Io moths we met in a previous episode, these spines, or urticating hairs in entomological lingo, contain venom released upon contact with a would-be predator or unlucky human. According to Dr. Isadora Maria Villas-Boas and colleagues, the composition of the saddleback’s irritating venoms is not fully known. However, their symptoms include mild to severe burning sensations reminiscent of a wasp’s sting. In some cases, a very uncomfortable and persistent rash may develop at the point of contact. Reactions of some folks can be more troublesome with burning sensations lasting for hours or days rather than for minutes, with accompanying headaches, difficulty breathing, gastrointestinal discomfort, and in severe cases anaphylaxis.  

Tiny brachonid wasps emerge from silken cocoons that festooned the exterior of a parasitized saddleback caterpillar.

One look at the saddleback caterpillar plainly explains its name. In the center of its back is a striking brown shield surround by a ring of white that closely resembles a saddle. Saddleback caterpillars eat a wide variety of plants in the forest and garden including oaks, elms, lindens, apples, plums, corn, blueberries, grapes, and apparently leaves of iris plants. With such a potent defense, one might think the saddleback has gained immunity from attack by enemies. Unfortunately for the saddleback, this is not the case. While hiking the Appalachian Trail a few years ago, I happened upon a most unfortunate saddleback caterpillar reliving a scene from the 1979 movie Alien, when the larval alien pops out of John Hurt’s chest. Festooning the back of the motionless caterpillar were dozens of tiny legless larvae. Spawned from eggs deposited in the saddleback caterpillar from a tiny wasp earlier this year, fully developed wasp larvae drilled their way through the skin of their victim and writhed on its back as they spun cocoons made of white silk. Observant gardeners have likely seen small white objects like these on the back of hornworms on tomatoes and identified them as eggs of some mysterious enemy of the caterpillar. In reality, these are cocoons of small parasitic wasps in the genus Cotesia. 

In a scene straight out of Aliens, wasp larvae emerge from their saddleback host and spin white cocoons in which to pupate.

Female Cotesia wasps hunt saddlebacks and other caterpillars on the foliage of plants. Upon encountering a suitable host, they jump aboard and rapidly deliver many stings using an appendage called the ovipositor. Once inside the caterpillar, eggs hatch and wasp larvae feed on the tissues of its host. However, to survive successfully, the tiny wasp larvae must avoid death by the caterpillar’s vigilant immune system. This is where a little help from mother comes along. In addition to depositing eggs, mother Cotesia injects a special virus known as a polydnavirus into the caterpillar. The polydnavirus disables the caterpillar’s immune system, paving the way for her young to develop without interference. Once development is complete, wasp larvae move to the surface of the caterpillar, burrow through its skin, and spin a cocoon on the exterior of their host. Stinging and being stung, part of the circle of life in a bug’s world. 

Watch this half-speed video as a parasitic wasp “stings” the saddleback and deposits her eggs.

Acknowledgements 

We thank Ellery Krause and Dan Gruner for bearing the stings of caterpillars and capturing the wasps that inspired this week’s episode of Bug of the Week. The wonderful textbook “Medical and Veterinary Entomology” by Gary Mullen and Lance Durden, and fascinating articles including “Effects of the polydnavirus of Cotesia congregata on the immune system and development of non-habitual hosts of the parasitoid” by N. Lovallo, B. A. McPheron, and D. L. Cox-Foster and “Venomous caterpillars: From inoculation apparatus to venom composition and envenomation” by Isadora Maria Villas-Boas, Giuliano Bonfá, Denise V. Tambourgi were consulted to prepare this episode.

The Site is Dead, Long Live the Site | Catalogue of Organisms

I'm moving house.

Over the past few years, Blogger has become somewhat less user-friendly behind the scenes. Nothing major, and certainly nothing I'm going to bore you with here, but enough that I've finally decided to take the step of breaking out and moving to my own site: varietyoflife.com.au. This site will incorporate material from both Catalogue of Organisms and Variety of Life, progressively merging them into a single guide to global biodiversity. Posts from both blogs have already been migrated over, though now I have the long task of editing and updating them to match the new format. In the meantime, check out the page on Prostigmata to get an idea of what I'm planning to do. New content will also be appearing regularly.

Thank you for reading Catalogue of Organisms, and I hope to see you in the new digs!