Month: February 2021

Mitey troubles for house plants: Twospotted spider mite, Tetranychus urticae

 

At only a fraction of a millimeter, twospotted spider mites still cause big problems for plants.

At only a fraction of a millimeter, twospotted spider mites still cause big problems for plants.

 

Two large dark patches on either side of body make it easy to see why they are called twospotted spider mites.

Two large dark patches on either side of body make it easy to see why they are called twospotted spider mites.

With ambient temperatures still hovering around the freezing mark, mischievous plant pests would seem months away. However, as days lengthen, the strong winter sun delivers much more energy to house plants, especially those placed near large picture windows with a southern exposure. For pests like spider mites, elevated temperatures can cut generation times by more than half. This and a few other factors we will learn in a moment contributed to a seemingly overnight explosion of spider mites on one hapless houseplant in my living room. Here’s part of the back story. When new plants arrive in a household, it’s always a good idea to give them a careful inspection just to see if they might be harboring uninvited guests. Keeping a watchful eye on new arrivals for a couple of weeks is also a good idea just to see how they are doing and observe any hitchhikers that may have accompanied them from the plant shop. Having failed to follow these ounce-of-prevention rules, a new arrival to our home recently blossomed into a spectacular outbreak of twospotted spider mites.

Mites are not insects. They belong to a related clan of arthropods, a subdivision of Arachnids called Acari. Unlike insects that have three body regions, spider mites have only two, a small region bearing the mouthparts and a large region bearing legs that comprise the rest of the body. The mite’s development starts with an egg that hatches into a 6-legged larva which molts into an 8-legged nymph. One more nymphal stage occurs before the mite sheds its skin and becomes an adult.

Thousands of spider mites puncture cells and remove green tissue from leaves creating a galaxy of white spots. This injury is called stippling.

Thousands of spider mites puncture cells and remove green tissue from leaves creating a galaxy of white spots. This injury is called stippling.

Twospotted spider mites are infamous worldwide as a major pariah of vegetables grown in fields and greenhouses, large and small fruits, ornamental trees and shrubs, and herbaceous ornamental plants, including those growing in front of my picture window. These cosmopolitan rascals feed on more than 200 plant species worldwide. They injure plants by piercing cells with tiny needle-like stylets that rupture cell membranes. Nutritious cell contents are then sucked into the digestive tract of the mite. By removing the green photosynthetic contents of cells, tiny white spots accrue on the leaf surface, creating a type of injury called stippling. When spider mites are abundant and their feeding prolonged, leaves may turn white as thousands of stipples coalesce. Eventually leaves discolor and may turn yellow, bronze, or brown before dropping from the plant. Heavily infested plants often appear to have encountered a blowtorch.

One fascinating and unique attribute of spider mites is their ability to produce silk. Super strong silk fibers function as mite highways connecting one part of the plant to another. Silk also provides a protective refuge from predators and adverse climatic conditions and acts as a substrate for depositing eggs and communicating with other members of the species.

In the warmth of a sunny window, populations of twospotted spider mites explode. A cloak of fine silk spun by thousands of spider mites provides a highway for the tiny suckers to move from one branch to another. In addition to transport, silk provides a refuge from predators and the perfect place for spider mites to deposit translucent spherical eggs. Heavy infestations like this one are often best resolved by disposing of a plant before mites spread to others.

Like secret agents in Spy vs Spy, in the intriguing world of mites, predatory phytoseid mites conduct search, find, and consume missions aimed at some of their favorite meals - eggs, nymphs, and adult spider mites. Image: John Davidson

Like secret agents in Spy vs Spy, in the intriguing world of mites, predatory phytoseid mites conduct search, find, and consume missions aimed at some of their favorite meals – eggs, nymphs, and adult spider mites. Image: John Davidson

Under natural conditions outdoors, twospotted spider mites are beset by attacks of predatory ladybeetles, lethal minute pirate bugs (arrrggghhh!), maniacal lacewing larvae, and predatory mites, among other beneficial insects. Unfortunately, these heroes are conspicuously absent from my living room. With thousands of spider mites already sucking the life from my plant, legions of mite eggs ready to hatch, generation times growing ever shorter in the strong winter sun, and a dozen uninfested house plants cowering nearby, the hapless house plant has now joined the remnants of last season’s vegetables in the compost pile. In a final act of contrition, plant and pests will fuel generations of microbes and decomposers like pillbugs and soldier flies we met in previous episodes in an ongoing circle of life.

Tiny lady beetles known as spider mite destroyers help reduce populations of spider mites in the wild.

Tiny lady beetles known as spider mite destroyers help reduce populations of spider mites in the wild.

Aye matey, minute pirate bugs suck the life from many small pests including lace bugs and spider mites. Image: Ada Szczepaniec

Aye matey, minute pirate bugs suck the life from many small pests including lace bugs and spider mites. Image: Ada Szczepaniec

Assisting spider mite destroyers are alligator-like lacewing larvae.

Assisting spider mite destroyers are alligator-like lacewing larvae.

Acknowledgements      

Fascinating articles including “The silk of gorse spider mite Tetranychus lintearius represents a novel natural source of nanoparticles and biomaterials by Antonio Abel Lozano-Pérez, Ana Pagán, Vladimir Zhurov, Stephen D. Hudson, Jeffrey L. Hutter, Valerio Pruneri, Ignacio Pérez-Moreno, Vojislava Grbic’, José Luis Cenis, Miodrag Grbic’ & Salvador Aznar-Cervantes”, and “ Featured Creatures, Common name: twospotted spider mite scientific name: Tetranychus urticae Koch (Arachnida: Acari: Tetranychidae)” by Thomas R. Fasulo and H.A. Denmark were consulted in preparation of the episode. Learn more about twospotted spider mites at this link: http://entnemdept.ufl.edu/creatures/orn/twospotted_mite.htm

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Ancient insect in a modern world: Silverfish, Lepismatidae

 

In the wild, shining silvery scales mark the presence of a silverfish amongst the leaf-litter of the forest floor.

In the wild, shining silvery scales mark the presence of a silverfish amongst the leaf-litter of the forest floor.

 

This week let’s time travel a little bit. Not the teeny, across the centuries travels Claire Fraser undertakes in Outlander. Nah, let’s journey back hundreds of millions of years long before T. rex walked the earth to the ancient origins of insects. In times when giant tree ferns ruled earth’s forests, primordial relatives of silverfish, the Triassomachilidae, foraged for starchy remains of plants on the verdant forest floor. Now fast forward several hundred million years to last Tuesday, when a handsome silverfish appeared at 6:10 am on the bathroom wall. With ancient decaying tree ferns conspicuously absent from my home, I wondered what delicacies silverfish discover inside a residential dwelling.

Among the most ancient of insects are the silverfish. On rare occasions I am graced by their presence early in the morning on my bathroom wall or maybe in the sink. My catch and release policy ensures they can find more natural surroundings when I release them outdoors.

Actually, we share many carbohydrate-rich food sources with plants found at the time of the world’s first silverfish. Modern food on the silverfishes’ menu include those high in starchy materials such as the cellulose found in paper goods and glue, the kind you were told not to eat in first grade, the glue that binds pages of books together. It is not surprising then, that some species of silverfish are important pests in libraries and museums where starchy materials abound. Other tasty treats for silverfish include natural fabrics such as linen, silk, and cotton, cereals, preserved meat, and dead insects, including other silverfish. Of course, in the geological time scale, frame houses are a fairly recent contrivance and typical natural habitats for silverfish are decaying logs and leaf litter, caves and crevices, and, for some species, ant nests.

When they are not on the wall, sometimes they are in the sink.

When they are not on the wall, sometimes they are in the sink.

The name silverfish was coined in part from the silvery scales found on the insect’s exoskeleton. The “fish” part apparently refers to the resemblance of the silverfish’s scales to those of fish. If you find silverfish scurrying around your home and wonder about the source, have a close look in dark, damp corners of the basement or other places where books or garments might be stored. Infested books or clothing can be placed in plastic bags and deposited in a freezer for a few days to kill attendant silverfish. Silverfish also thrive in conditions of high humidity and dehumidifiers placed in damp rooms may help reduce the suitability of these locations for silverfish. Removing clutter, storing books and garments in airtight containers, and vacuuming closets and storage areas will also help reduce populations of silverfish and other nuisance pests around the home. So, where is the wellspring for my silverfish? Well, just beneath my bathroom floor lies a pantry used to store paper goods and other household items. Sometimes it is a bit musty and maybe it could use a more regular visit with a vacuum. But, I have to admit, there is something remarkable about a morning greeting by a creature older than dinosaurs. I usually just catch these old timers in a paper cup, warn them to socially distance especially when predators are near, and release them in the wild.  

Acknowledgements

To learn more about silverfish, please check out the fascinating fact sheet “Common name: silverfish, scientific name: Lepisma saccharina Linnaeus (Insecta: Zygentoma: Lepismatidae), Introduction – Distribution – Description – Life Stages and Biology – Hosts – Economic Importance – Survey and Detection – Management – Selected References” by Eleanor F. Phillips and Jennifer L. Gillett-Kaufman. It can be found at this link: http://entnemdept.ufl.edu/creatures/URBAN/silverfish.HTM

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Lovebugs, kissing bugs, and other insects engaged in intimate activities. What’s all this coziness about?

 

This pair of Hercules beetles doesn't mind a public display of intimacy. By guarding his mate, he may prevent other suitors from mating with her. Males bear impressive horns used in combat with other males.

This pair of Hercules beetles doesn’t mind a public display of intimacy. By guarding his mate, he may prevent other suitors from mating with her. Males bear impressive horns used in combat with other males.

 

A dinner date of fall webworms hits the spot for awesome wheel bugs.

A dinner date of fall webworms hits the spot for awesome wheel bugs.

Next weekend we celebrate Valentine’s Day, a day named in honor of a third century Italian saint commemorated throughout the centuries by exchanging notes of love, romance, gifts of flowers and candy, and boatloads of affection. Several amorous characters take center stage in this Bug of the Week. Whether it’s a horny male Hercules beetle out for a romp on a stump, wheel bugs enjoying an intimate dinner of fall webworm caterpillars, or teenage cicadas celebrating a day in the sun after seventeen years underground, conjugal visits abound in the insect world. Let’s find out why.

For many animals, copulation is a short-term affair, measured in mere minutes or sometimes fractions thereof. However, insects depicted in this episode linger long with their mates, in some cases copulation lasts for hours and even days. Red-shouldered bugs we met in a previous episode may copulate for eleven days. How exhausting! Prolonged copulation and post-copulation “riding” of a male on the back of its mate is common in many orders of insects. By denying interlopers access to a female, prolonged mating and post-copulatory guarding by the male helps ensure that his sperm will be the ones which fertilize his mate’s eggs. In the world of insects, often the last mating before eggs are laid is the one that counts. This likely explains the oft observed pairings of so many male and female insects.  

Lovebugs conjoin for hours during the mating season. FYI: male on the left, female on the right.

Lovebugs conjoin for hours during the mating season. FYI: male on the left, female on the right.

Long before Disney coined the term “Love Bug” for a rambunctious Volkswagen beetle, denizens of Florida and the Gulf states knew of another kind of lovebug. The Floridian lovebug is a small fly with a red thorax and black body and wings. The name “lovebug” derives from the fact that these small flies are often found intimately entangled. Lovebugs belong to a family called the Bibionidae. As larvae, bibionids eat decaying plant material and are important decomposers like isopods we met in a previous episode. After completing development in the soil, they pupate and emerge as adults. Adult flies do not bite or sting, but vast numbers emerge in spring and fall creating a real nuisance to residents in southern states. In addition to entering homes and bumbling about the garden, lovebugs splatter windshields of cars and trucks creating hazardous driving conditions. They become numerous enough to clog radiators of cars, causing them to overheat. One way to avoid these lovers is to drive in the late afternoon or evening when lovebugs are less likely to take wing.

Many Insects have prolonged copulation and often males guard their mates for hours or days following copulation. Just for fun, let’s look at a few. From first to last, they are: Damselflies coupled in the “heart” position for long periods of time; conjoined spur-throated grasshoppers basking in sun; camera-shy periodical cicadas that will appear by the trillions this spring when Brood X appears; peripatetic milkweed bugs playing push me, pull you; gorgeous dogbane beetles enjoying dinner and a date on their heart-stopping host; male margined carrion beetles engaging in shaky business with their mates; female thread-waisted wasps dining on pollen while their mate hitches a ride; and adorable male horn-faced mason bees fending-off suitors while guarding their betrothed.  

Kissing bugs get their name by sucking blood from tender spots, including lips of hapless human victims.

Kissing bugs get their name by sucking blood from tender spots, including lips of hapless human victims.

With respect to kissing and kissing bugs, many would agree that kissing ranks right at the top when it comes to affection. However, the kiss of the kissing bug can be oh, so much more than that. Kissing bugs belong to a family of sucking insects called assassin bugs. Assassin bugs are predators, predators with long beaks which they use to suck blood from many other kinds of animals. Kissing bugs take the act of predation one step further. Their primary source of food is the blood of vertebrates, including mice, dogs, and humans. During the day, kissing bugs hide in crevices in plaster, cracks between boards, or in gaps in thatched roofs. At night, these little vampires leave their refuge and quietly seek unsuspecting humans to suck their blood. They may feed on any exposed body part, but look out, their dining preferences swing to tender tissues on people’s faces, especially the lips, hence the name kissing bugs. In southern Texas, Central and South America, kissing bugs are common. For most people the bite of the kissing bug may go unnoticed, or it may leave no more than a small red mark. But for those allergic to the saliva of kissing bugs, itchy welts, rashes, and swelling can occur. As with the introduction of any foreign protein into the body, anaphylactic reactions are a concern. A greater worry associated with kissing bugs is their ability to vector a nasty parasite called Trypanosoma cruzi, the causal agent of a sometimes fatal disease called Chagas disease. The parasite is ingested by the kissing bug as it feeds on an infected animal. Carried in the gut of the kissing bug, the parasite issues forth when the kissing bug defecates on a victim’s skin. An abrasive scratch by the victim or a small puncture in the skin allows the parasite to enter the body and wreak havoc. How disturbing! While most common in regions of Central and South America, kissing bugs can be found as far north as Pennsylvania on the east coast and California on the west coast. If your adventures take you to rural areas of Mexico, Central or South America where Chagas disease is endemic, always sleep inside your netting and remember, no kissing the kissing bugs, even if it is Valentine’s Day!

Acknowledgements

The intriguing article “The adaptive significance of mate guarding in the soapberry bug, Jadera haematoloma (Hemiptera: Rhopalidae)” by Scott P. Carroll, the great Featured Creature fact sheet “common name: lovebug scientific name: Plecia nearctica Hardy (Insecta: Diptera: Bibionidae) Introduction – Classification – Distribution – Description – Key to the Species – Dilophus sayi – Behavior – Hosts – Economic Importance – Management – Selected References” by H.A. Denmark and F.W. Mead,  and the CDC Chagas disease website were consulted to prepare this episode. Bug of the Week thanks Marcia Shofner for the inspiring this heart-warming Valentine’s Day episode.

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Chilly romance for winter stoneflies – Plecoptera: Capniidae and Taeniopterygidae

 

Snow and ice don’t cool romance for amorous winter stoneflies.

Snow and ice don’t cool romance for amorous winter stoneflies.

 

While most insects are scarce and inactive during winter months, winter stoneflies romp about riverbanks and nearby environs even in the dead of winter. Photo credit: Steve Black

While most insects are scarce and inactive during winter months, winter stoneflies romp about riverbanks and nearby environs even in the dead of winter. Photo credit: Steve Black

This week we turn to the Bug of the Week mailbag where we received a picture of an unusual winter-active insect found on the trunk of a tree. Let’s visit stoneflies, curious amphibious insects whose lives are split between two worlds; a life aquatic in their youth and romantic interludes on land as adults.  While many insects migrate or enter a hibernal torpor called diapause during this frosty season, winter stoneflies are in their glory. Special compounds including glycerol, proteins, and sugars act like antifreeze and prevent stoneflies from freezing to death as they cavort on snow covered stream banks. These ancient insects can be found on stones, vegetation, and bridges near small, fast-moving streams. These week’s star was sighted in a nursery near a major river in western Maryland loitering on the bark of a tree. 

Adult winter stoneflies are dark brown or black and are active day and night. In their youth, stoneflies live in fresh water, rushing streams and rivers. Juvenile winter stoneflies, called nymphs, graze on submerged aquatic vegetation or decaying organic matter. Other species have abandoned a vegan diet and eat aquatic insects, including other stoneflies. Stonefly nymphs obtain oxygen from the water through delicate gills lining the neck, thorax, or abdomen. Most immature insects shed their skin or molt just a few times as they develop. However, some species of stoneflies may molt more than 20 times before leaving the water as adults in search of mates. The remarkable transformation from nymph to adult transpires at the edge of the stream as the nymph emerges from the water and latches onto a stone, log, or plant. The exoskeleton splits along the midline and the adult stonefly emerges like a wraith from the cast skin. When the exoskeleton hardens, adults walk and fly to find mates. As adults, food choice differs on a species basis. Some eat lichens, algae, or vegetation, but others gain all necessary nutrients as nymphs and never feed as adults. Winter stoneflies are relatively weak fliers and seem to prefer walking and running to flying. However, other species of stoneflies are good fliers and are attracted to porch lights and, unfortunately, bug zappers.

Stonefly courtship is a curious matter. A hopeful guy stonefly strikes the surface of a resting place, such as a small branch or a stone, with its abdomen to create a specific drum beat. If a female of the same species is nearby and favorably impressed by his rhythm and sound, she will drum a reply with her abdomen. The percussive duet continues and if both like what they sense, the deal is sealed and they mate. After mating, the female stonefly will swoop to the surface of the water to deposit her eggs. This is a season of joy for fish living in stonefly laden streams. Trout, steelhead, and other freshwater fish find stonefly nymphs and adults delectable. Both adult and juvenile stoneflies are an important source of food for denizens of our streams. Fisherman have taken advantage of this passion and created a variety of lures that mimic stoneflies with colorful names like Montana Stone Yellow and Henry’s Fork Yellow Sally.

Plucked from a riverbed, a stonefly nymph dashes to return to its watery realm. Shed skins of stoneflies cling to logs and stones near riverbanks where nymphs molt and become adults. On wintry days, males roam icy landscapes and even slowly moving humans in search of mates. Male stoneflies drum their abdomen on substrates including small branches and stones along the river to attract a mate. While inaudible to the human ear, a receptive female will catch his vibe and signal her willingness to mate by returning his percussive performance with one of her own. Who says drummers aren’t romantic?

Clean, fast-moving streams and rivers are excellent places to hunt winter stoneflies.

Clean, fast-moving streams and rivers are excellent places to hunt winter stoneflies.

Stoneflies are also important indicators of water quality. Streams with heavy sediments, low oxygen content, or pollutants do not support a diversity or abundance of stoneflies. Stoneflies emerging from your local stream are a positive sign of a healthy environment. So, during the next couple of weeks, take a walk on a sunny afternoon and visit a small stream or river to seek the stonefly. The best viewing is when stream banks are covered with snow and stoneflies clamber from the chilly waters below. The winter stoneflies featured in this Bug of the Week were observed on warmish afternoons on a small footbridge spanning the Little Patuxent River in Columbia, Maryland, on the Billy Goat Trail along the mighty Potomac River in Maryland, near the Monocacy River in Frederick County, Maryland, and along the banks of Pidcock Creek near Lambertville, Pennsylvania.

References

Bug of the Week thanks Steve Black for sharing his great image of a winter stonefly discovered on a tree-trunk. The fascinating book “Aquatic Entomology” by W. Patrick McCafferty was used as a reference for this Bug of the Week. Here is a link to a really nice article detailing the stonefly’s clever strategies for surviving winter: https://blogs.scientificamerican.com/guest-blog/winter-stoneflies-sure-are-supercool/

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