Month: November 2022

On recent visits to the thriving metropolis of Washington, DC, we met dastardly soft scales and rambunctious red-shouldered bugs enjoying meals served-up by oak trees and golden rain trees lining the avenues of our nation’s capital. This week we return to DC to visit glorious crapemyrtle trees and scandalous scale insects intent on turning crapemyrtle branches snowy white. Originally native to Asia, crapemyrtles traveled with botanical explorers from their aboriginal homes to gardens in Europe and the Americas more than 250 years ago. As North America warms, the range of crapemyrtles has expanded from subtropical southern states to mid-Atlantic locations, including Maryland and DC where milder winters and hot summers allow them to thrive. But, as is often the case with non-native plants, sometime after their arrival in a new land, their pests from afar soon follow them to the invaded realm. This was the case for crapemyrtles, when in 2004 the crapemyrtle bark scale, a type of felt scale, was discovered in Richardson, TX. Since the first detection in 2004 it has marched steadily northward to North Carolina in 2016, to Virginia in 2017, and to Maryland in 2020. Range expansion of this and many other scale insects happens in a variety of ways. Infested nursery stock shipped from southern states may convey scales to new locations. Some scale insects climb onto the feet of birds, hair of mammals, and bodies of flying insects and become unwittingly transported by these other animals from an infested to an uninfested tree. In an even stranger twist, some scale insects actually utilize “takeoff” behavior to help them become airborne and then ride the wind from one plant to another. Insects as aeronauts, how cool is that! 

Monocultural plantings of crapemyrtles and other street trees often support outbreaks of pests in cities. Beneath the snowy white egg-sac, we find a bizarre female crapemyrtle bark scale. She can lay more than 300 bright pink eggs. Eggs hatch into pink crawlers that sally forth to settle new patches of bark. They molt before producing their own egg-sac. Heavy infestations kill branches and foul the bark with honeydew, which supports the growth of ugly sooty mold fungus.

Like the aforementioned soft scale, crapemyrtle bark scale feeds on nutrient-rich plant sap called phloem. To gain sufficient nutrients for growth, development, and reproduction, vast quantities of phloem are imbibed. Once processed, any remaining liquid is excreted in the form of a sugary waste product called honeydew. Honeydew rains down from infested plants onto vegetation, sidewalks, vehicles, and furniture below, creating a sticky mess that also attracts stinging insects like paper wasps, yellow jackets, and honeybees. Adding insult to injury, honeydew serves as a substrate for the growth of a nasty black fungus called sooty mold which discolors bark, leaves, and other objects on which it lands. Removal of vital plant sap and damage caused by thousands of piercing mouthparts can result in branch dieback and death of crapemyrtles.

Life gets busy for crapemyrtle bark scales when tiny pink nymphs hatch from tiny pink eggs laid by the female in her snowy white, felt-like egg-sac (a.k.a ovisac) which encloses the she-scale and her young. These nymphs go by the name of crawlers and that’s exactly what they do, crawl to new parts of the crapemyrtle and settle down to suck sap from their crapemyrtle host. Each female can lay from 100 to more than 300 eggs. In warm regions there may be four generations annually and it is easy to see how populations can explode seemingly overnight. While crapemyrtles are the primary target for this rascal here in the US, this scale has also been found on more than a dozen other plant species in the US and other parts of the world, including beauty berry, pomegranate, boxwood, persimmon, privet, brambles, and many others.

 So, is there any good news here? You bet. Several members of Mother Nature’s hit squad, including lady beetles, lacewings, and parasitic wasps are known to attack and kill this felt scale. However, in many cases once the scale gets rolling even these beneficial insects may not be enough to put a beat-down on this pest. Many potent insecticides are available to kill both immature and adult stages of the scale. Here in the DMV an outstanding corps of certified arborists is available to help homeowners and urban foresters manage this invader. Let’s hope that all crapemyrtle Christmases aren’t white.   

Acknowledgements

“Biology and Management of the Crapemyrtle Bark Scale: Landscape and Nursery Grower” by Erfan Vafaire, Mike Merchant, and Mengmeng Gu, “Crawler behaviour and dispersal” by David J. Greathead, and “Phoretic dispersal of armored scale crawlers (Hemiptera: Diaspididae)” by J. Magsig-Castillo, J. G. Morse, G. P. Walker, J. L. Bi, P. F. Rugman-Jones, and R. Stouthamer were used to prepare this episode.

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This week we delve into the Bug of the Week mailbag to help solve a mystery of “fuzzy” somethings, at the base of white oak leaves found on a tree near the gentle Choptank River on Maryland’s eastern shore. These curious fuzzy somethings are the handiwork of gall wasps, one of the most diverse groups of gall-formers found on plants. Galls are abnormal growths on plants created by several species of insects, mites, and some microbes, that secrete potent chemicals into the plant’s undifferentiated tissues. These chemicals derail the normal developmental processes of the plant and create food and refuge for the insect or mite within the gall at the expense of the unwitting plant host. We met other gall-making insects including those distorting leaves of black gum, elms and hickory in previous episodes.

The gall wasp family, Cynipidae, is more than 1,300 species strong with most generating unusual growths on woody plants, but some actually parasitizing other species of wasps. Dozens of species of wasps in this family have evolved intimate relationships with different species of oak. The diversity of galls on the leaves, branches, and acorns of oaks is awesome. Each species of gall wasp creates its own distinct and unique gall. Some look like bullets, others appear to be clusters of wool, some look like apples, and still others are the visage of grotesque horned creatures attached to a branch. The video accompanying this episode provides a smidgeon of this diversity of galls discovered on oaks in Maryland.

Let’s visit some gall wasps on oak. Strange horns decorate the outside of the horned oak gall wasp while the pupa develops within. These small round leaf galls are home to developing wasp larvae. When we open these green round galls, we can see the larval cell with an exit hole used by the wasp to escape the gall. Rough bullet galls wear exit holes outside and inside you see where the wasp chewed through the larval chamber and gall to get out. Pretty midrib galls and a couple spangle galls decorate this oak leaf. Potato-like galls and pouch galls adorn small twigs. Green spongy oak galls in summer turn to brown papery balls in autumn beneath oak trees.

Let’s walk through the life cycle of one cool but dastardly trouble maker, the horned oak gall wasp, Callirhytis quercuscornigera, to learn a bit more about these fascinating creatures. The saga begins in spring shortly after bud-burst of oaks when female wasps escape from their nursery inside the gall through one of the strange looking horns. These wasps are all females and are part of generation produced asexually through a remarkable process called pathogenesis. Many species of insects reproduce parthenogenically, such as aphids and scale insects we met in previous episodes. You go girls!  Wasps emerging from leaves are poor flyers and move just a short distance to developing leaf-buds, where they lay eggs. Single eggs hatch and induce the formation of an inconspicuous leaf gall. Later that summer both male and female wasps emerge from the leaf gall, mate, and females deposit girls-only eggs in tender green twigs. These eggs hatch and induce the formation of a small woody gall that enlarges over the course of the summer. Some 30 months later, fully developed female wasps emerge from large galls to complete the life cycle.   

Although details of gall inducement are not fully known, the act of egg-laying and the growth-altering chemicals subsequently released by the larva of the wasp cause the multiplication of nutritive plant cells inside the gall and abnormal development of the infested plant tissue. Wasp larvae consume these cells while non-nutritive cells proliferate to form the bizarre and characteristic gall. Inside the relative safety of the gall the larva grows as the gall enlarges. As development nears completion, the plant forms a tissue layer which can be a relatively tough, seed-like cell around the larva. Within this small chamber the larva transforms into a pupa from which the adult wasp emerges. Using powerful jaws, the wasp cuts it way out of the chamber and the surrounding gall and flies off to find food and a mate. Development from egg to adult often takes place in the gall while it is attached to the plant. However, in some species like the jumping oak gall, Neuroterus saltatorius, the gall breaks from the plant and falls to the ground with the larva inside. While completing development in the gall on the ground, the movement of the larva within can make the gall jump in the air. That’s right Little Orphan Annie, not leapin’ lizards, but leaping galls instead!

Acknowledgements

The fascinating article “Biology of Callirhytis cornigera (Hymenoptera: Cynipidae) and the Arthropod Community Inhabiting Its Galls” by Eileen A. Eliason and Daniel A. Potter, and the Maryland Biodiversity Project were used to prepare this article. Special thanks to Sue Hauser for providing the image of fuzzy gall wasps on oak leaves and inspiration for this episode.

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Last week while enjoying record breaking warm weather with a hike along the mighty Potomac River in Mercersville, MD, I was assaulted by two tiny terrors that pack a surprisingly large wallop for their size. In previous episodes we met dastardly Aedes, Culex, and Ochlerotatus mosquitoes equipped with hypodermic-like mouthparts perfect for inserting into small capillaries to obtain blood used by females to develop eggs. Although mosquito bites are itchy, to me their bites pale with respect to the aggravation and burning sensation brought on when legions of black flies and no-see-ums visit my skin.

Black flies use jaws with serrated edges to slash flesh and sever tiny blood vessels. As blood pools in the wound, the black fly laps it up. Only the female black fly has the blood lust. She exploits this rich protein source to produce as many as 800 eggs over the course of her lifetime. Males are the gentler gender and consume nectar from flowers, as do females when not taking blood. With her load of fully developed eggs, the female black fly visits running mountain streams or other fresh water sources and deposits her eggs on rocks, logs, emergent vegetation, or directly into the water. Eggs hatch and larvae attach to rocks and other submerged structures and graze on small plants and animals on the surface of their substrate.

Fast moving streams and rivers are prime breeding sites for black flies. A rock plucked from the river harbors a black fly larva hiding in the vegetation. A series of video clips show the expanding abdomen of the black fly as she feeds. When she is done, my flesh continues to ooze blood from severed capillaries. Watch as an even tinier no-see-um tanks up while feeding on my arm.

The wound of the black fly is quite something to behold. While the bite itself is cloaked by anesthetics administered in the saliva of the fly, the aftermath can be quite disagreeable. For many victims of their bite, reddish-purple blood spots appear beneath the skin at the site of each bite as the body reacts to anticoagulants and other allergens injected into the site of the wound. These red welts were accompanied by intense itching that can last several days and may be accompanied by fever, swelling, and nausea. There are reports of domestic animals dying when legions of black flies attack. The direct injury caused by black fly bites is the lesser of the evils visited unto humans by these tiny flies. In several countries in Central and South America and Africa, black flies carry nasty filarial worms capable of invading the human body. They occupy small tumors beneath the skin. In some cases, these filarial worms take up residence in the eye and cause permanent sight loss known as river blindness or Robles disease. Yikes! Glad our Maryland black flies do not carry such diseases.

Just downstream from Mercersville, near historic Harper’s Ferry, black fly populations hit intolerable levels on the Potomac. The Maryland Department of Agriculture and Department of Natural Resources treated a section of the Potomac with a biological control agent, Bacillus thuringiensis israelensis (BTi), to quell populations of black fly larvae developing in the river.  This bacterial insecticide is derived from a naturally occurring soil microbe and has been used to mitigate several types of aquatic and terrestrial fly larvae. Government agencies reported that “the treatment may cause temporary discoloration of the water, but it is completely nontoxic and is not harmful to humans, fish, crabs or other aquatic invertebrates.”

And just how tiny is tiny? Well, black flies range in size from about 1 to 5 mm and sometimes larger, smaller than the width of a tic tac. Our second tiny terror, no-see-ums, a.k.a. biting midges, can be even tinier than black flies at 1-3 mm. Little wonder they are called no-see-ums. While these minute vampires are hard to see, their bite is easy to remember with a characteristic burning sensation. Itching associated with these bites can last several days. Like black flies, females use cutting mouthparts to sever capillaries and sucking mouthparts to imbibe the blood needed to produce eggs. Also like black flies, male and female no-see-ums obtain carbohydrates from plant nectar. Larval no-see-ums are aquatic or semi-aquatic, found in both water and in moist soils near rivers, marshes, ponds, and lakes; tree holes; and decaying vegetation and fruit. In addition to the nuisance they become when abundant, they carry serious diseases of humans and domestic animals in some parts of the world. In Central and South America, parts of Africa, and some Caribbean islands, no-see-ums carry tiny roundworms that infect humans and cause skin lesions. In parts of Africa, Europe, and Asia, a deadly virus called African horse sickness (AHS) is carried by no-see-ums to horses and their close relatives. Fortunately, at this writing, AHS is not known to occur in Maryland or other parts of the US. Lucky us, that for the most part here in the DMV, these tiny terrors remain mostly annoying and not distributors of disease.

Acknowledgements

Excellent references by J. F. Butler (University of Florida) and J. A. Hogsette (USDA) on black flies, and C. Roxanne Connelly on no-see-ums (University of Florida) as part of the University of Florida’s ‘Featured Creature’ series, and M. T. James and R. F. Harwood’s “Herms’s Medical Entomology” were consulted for this episode. To learn more about “The Black Fly Suppression Pilot Program in Maryland”, please visit the Maryland Department of Agriculture website at this link: https://mda.maryland.gov/plants-pests/Pages/Black-Fly-Program.aspx

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In previous episodes we explored the travails of iconic monarch butterflies on the eastern and western coasts of North America where these long-distance travelers struggled with habitat destruction, climate change, disease, and pesticides. Unbeknownst to many folks is the fact that monarchs are not the only migratory visitors to the DMV. Several other insects, including another beautiful orange and black butterfly, the variegated fritillary, visit the DMV in the warmth of summer and head south to escape our chilly winters. Recently, an observant naturalist inquired about the migratory behaviors of these lovely peripatetic visitors.

Here’s the deal. Several years ago, I willingly surrendered the battle to maintain a lawn as a monoculture of exotic grasses like fescue or zoysia and as a result, floristically speaking, my yard has become quite diverse. Among the winners in the ground cover competition, particularly in shady spots and landscape beds, violets rule. With regularity, I notice significant nibbles and bites at the margins of the omnipresent violets, and upon closer inspection several glorious larvae of the variegated fritillary were found grazing on violet leaves. These tiny caterpillars were the spawn of orange and black variegated fritillaries that appear in my landscape each year, attracted by the bountiful floral resources needed for their sustenance.

In many states the variegated fritillary is a migrant, moving ever northward from its winter redoubts in the south. Much like our friends the monarchs who chase fresh patches of milkweeds as they move northward from overwintering grounds in Mexico, variegated fritillaries expand their range northward and colonize fresh crops of host plants for caterpillars and flower blossoms for adults. One has to wonder if the northern migration also helps them escape from hungry predators or stealthy parasitoids that hunt them in their overwintering grounds. Following their arrival in the DMV and well into autumn, they will be regular visitors to open sunny areas such as fields, pastures, lawns, and along the edges of roads where females consume pollen and nectar from butterfly weed, milkweed, dogbane, zinnias, cone flowers, red clover, and a variety of other plants. When they are ready to lay eggs, females seek nutritious plants such as mayapple, lamb’s ear, purslane, and violets, on which to lay eggs.

Whether munching leaves of hooded violets or petals of a pansy, variegated fritillary caterpillars find these members of the Viola clan delectable. Adults love to nectar on cone flowers in the summer and can be seen in late autumn basking in the sun among fallen leaves before heading south for the winter.

The caterpillars are gorgeous, bedecked in bright bands of orange and white. The body is festooned with stout black spines. Unlike some caterpillars we visited in previous episodes, these spines are not reported to deliver a nasty sting. In addition to consuming my volunteer violets, I have discovered several fritillary caterpillars devouring the petals of my pansies, another member of the viola clan. Variegated fritillaries will be resident and complete three generations over the course of the summer here in Maryland. In some states above the Mason-Dixon Line only two generations occur each year, and in colder reaches of the US and southern Canada, but a single annual brood is found. Here in my landscape, they are one of the last butterflies seen well into fall. As the days grow shorter and the night times chillier, the last of the variegated fritillaries will head south for warmer overwintering grounds. Those not heeding Mother Nature’s warnings face a chilly demise if they remain here in the DMV, thereby removing their foolish genes from the population of these fascinating vagabonds.

Acknowledgements

“Caterpillars of North America” by David Wagner, “A Swift Guide to Butterflies of North America” by Jeffrey Glassberg, and the Maryland Biodiversity Project were used as references for this episode. Bug of the Week thanks Adreon Hubbard for providing the nice image of a variegated fritillary and providing inspiration for this story.

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