Month: November 2020

Holiday season is baking season. Pies, cookies, cakes, and breads are comfort foods many crave on chilly days. During this season of culinary delight, cupboards and pantries receive lots of attention and activity. On a recent socially-distanced visit to a friend’s home, we noticed tiny moths flitting about the kitchen. A peek inside the pantry revealed more than a minor swarm of said moths. During this holiday season, many hopeful bakers will open pantries and be greeted by clouds of these small wonders, a cosmopolitan raider of the pantry, the Indian meal moth, Plodia interpunctella. While fascinating for entomologists, this is an unwelcome surprise for most folks.  

The adult stage of this insect is a rather small moth just slightly larger than ½ inch in length, with wings banded white and rusty red. They flit about the pantry or cupboard in search of mates and tasty products rich in carbohydrates, fats, and proteins. One recent infestation in my cupboard raged in a package of organic cashews. Within the package, small cream colored caterpillars spun silken webs and sallied forth to consume the nutritious nuts. In addition to spinning silken galleries, larvae deposited frass, the digested remains of their meal. The voided frass was entangled in silken strands to form a nasty messy web. Two excellent clues signaling the presence of meal moths are the presence of silk and frass within a bag of flour, grain, seeds, or pet food. After larvae complete development, they may gnaw holes and escape their plastic prisons. Nomadic caterpillars are often found wandering about the walls and ceiling of the pantry in search of a protected spot to spin cocoons and develop into pupae. Sometimes vagabond larvae enter cracks between shelves, lids of jars, electrical sockets, or seams behind baseboards to pupate. Soon the next generation of adults will appear, intent on finding new bags and boxes of stored products to infest.  

Within a plastic bag, scads of meal moth caterpillars spin silken webs and deposit frass while devouring my once tasty organically grown cashews. While caterpillars are a rich source of protein, this much extra protein with my nuts I don’t need.

How do meal moths colonize pantries in the first place? It is possible that original infestations of meal moths arrive with cereal, seeds, dried fruit, or grain as a few tiny eggs within a package from the store. After hatching from eggs, small caterpillars in a bag of seeds in the back of a closet could go unnoticed, but this vanguard is capable of generating sufficient moths to initiate a full blown mothagedon. Meal moths also survive outdoors and are commonly found in caches of nuts or seeds stored by squirrels or rodents. Adult moths originating outdoors can invade indoor pantries during warm weather when doors and windows are wide open. Mice often enter homes in autumn and winter seeking shelter and bringing stockpiles of seeds with them. These seeds might arrive contaminated with the associated moth eggs and may become a source of infestations indoors.  

What should you do if you find these rascals in a pantry or cupboard? First, remove all goods and products from the storage area. Vacuum the cupboard, pantry, or cabinet like there is no tomorrow. Carefully inspect all cracks, corners, crevices, and seams in the cupboard and remove any larvae or pupae you find. Seal as many of these refuges as possible with caulk. Remove and replace loose paper used to line shelves. Inspect any pots, pans, glasses or other items occupying the pantry where food will be stored and remove any meal moths on these items as well. Inspect opened and unopened bags and boxes of food for signs of silk, frass, larvae, or moths. If in doubt, toss it out. My pantry pest guru recommends the “deep chill” treatment for unopened packages you might want to salvage, but are suspect by association. Place unopened bags in the freezer for one week, remove them for one week, and then freeze again for a final week. The intermittent week of thaw tricks eggs into hatching and the tiny caterpillars are then killed by the second trip to subzero land. When you purchase items that might serve as food for meal moths, seal them in strong plastic storage containers with tightly fitting lids. This will help prevent any moths you might have missed during the crusade from laying eggs that hatch into larvae capable of infesting your food. Try not to store prime foods like grain or dried fruit for very long periods of time. The longer stored products remain on a shelf, the more likely they are to be infested by an itinerant moth that happens by.  

One approach useful in alerting you to an incipient invasion of meal moths is to purchase and deploy pheromone traps. These small triangular boxes are placed inside your pantry or cupboard. Inside the box is a sex pheromone bait that attracts the male meal moth from many feet away. The ever-hopeful male senses the pheromone, a chemical signal released by a female, and is tricked into believing that a receptive beauty waits inside the open-ended trap. He flies inside to find his mate, but instead becomes ensnared by a sticky substance lining the inside of the trap. By placing these traps within a pantry, you can detect the emergence of male moths that may be the harbingers of a burgeoning population of moths in your cupboard. This advanced warning serves as a signal to initiate a search and destroy mission. Good luck hunting moths and protecting your baking supplies during this season of culinary delight.   

Acknowledgements 

We thank Linda and Jeff for sharing their relentless Indian meal moths with Bug of the Week and Dr. Nancy Breisch for the wealth of information and advice about bugs. The Handbook of Pest Control, Ninth Edition, by Arnold Mallis was used as a resource.

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Just before Thanksgiving kicks off the holiday season, scads of questions show up in my mailbox about hordes of tiny flies buzzing around fruit bowls, kitchen sinks, and counters tops. They seem to appear from nowhere and lend credence to Aristotle’s notion of spontaneous generation, the theory that living organisms like flies somehow originate spontaneously from non-living or putrefying things. To help untangle this mystery, consider the change of seasons.  Late autumn in the DMV and many other parts of our land is characterized by cool damp weather. Moist evenings and mornings punctuated by warmish days are nearly ideal for decomposing tons of leaves, fruits, and other vegetable matter, the accumulated bounty of Mother Nature’s efforts during spring and summer. This week of Thanksgiving, my compost pile is a writhing mass of invertebrates intent on converting vegetable protein into animal biomass as quickly as possible. On warm days, a cloud of fruit flies hovers over my compost and some of these winged raiders undoubtedly infiltrate my home when doors open.

Like many kitchens, mine is home to a bowl of fruit that occasionally contains one item gone a little squidgy. Yeasty odors of acetic acid and ethanol emanating from an over-ripe banana serve as powerful attractants for fruit flies. After arriving at a slightly brown banana, the female fruit fly deposits eggs. Each gal lays roughly 500 eggs during the course of her life time. Small translucent larvae hatch from the eggs. They glide through the overripe fruit slurping-up nutritious fermenting fluids as they develop and grow. With warm ambient temperatures, fruit flies can complete a generation in less than two weeks. With their capacity for reproduction, populations around the fruit bowl can explode seemingly overnight. One careless week, I neglected to empty the stainless steel compost bin on my kitchen counter and I was rewarded with several hundred fruit fly maggots happily growing in the bin. Yikes!

Fruit flies can also enter home as stowaways with overripe fruits or vegetables from the market or garden. These goods may arrive preloaded with a complement of eggs or tiny larvae. To reduce chances of bringing home an infestation, inspect your produce carefully and wash fruits or vegetables before you set them out in a bowl. If fruit is unrefrigerated and displayed in a bowl, check it out regularly and toss over-the-hill items before they generate flies. Fruit flies often breed in sink or floor drains, garbage pails, or recycling containers in homes, restaurants, and offices where decomposing organic material accumulates. Inspect these areas regularly, clean up spills, and disinfect surfaces. For the cloud of fruit flies wafting around your home, consider building a vinegar trap to catch and kill these noisome rascals.  Traps can be purchased commercially and several trap designs are available on the internet. My do-it-yourself vinegar trap consists of an 8 oz. clear plastic tumbler filled with 4 oz. of apple cider vinegar or wine vinegar and a few drops of dish detergent. Within 24 hours of placing the trap on the counter, more than 100 fruit flies were lured to their death.  One clever modification of the trap includes fastening a bit of plastic wrap over the lid of the vessel with rubber bands a poking a few holes in the plastic. Apparently, this allows fruit flies to enter but confounds attempts to escape should they change their tiny minds about a vinegary death by drowning.   

More than just an indoor nuisance, several invasive species of fruit flies have now established in our region. The spotted-wing drosophila, Drosophila suzukii, first detected in the US in 2008 in California, has now spread from coast to coast and border to border. It is a major pest of strawberries, blueberries, raspberries, black berries, and cherries, and crop losses in the United Sates alone are estimated to exceed hundreds of millions of dollars annually. If spotted-wing drosophila was not enough, a second dastardly fruit fly, the African fig fly, Zaprionus indianus, first detected in Florida in 2005, has now spread to the Canadian border and can also be found here in the DMV. African fig flies infest a broad range of plants, including berry crops as well as figs, grapes, and cherries. Unlike spotted-wing drosophila, female African fig flies generally cannot cut through intact fruit skin to lay eggs; they instead are thought to oviposit (deposit eggs) into or near pre-existing cracks and wounds. In some varieties of grapes, the African fig fly may actually out-compete its Asian relative, the spotted-wing drosophila.

African fig fly is an invasive fruit fly species that was first detected in the United States in 2005 and has since established in Maryland. Adults can be identified by the white and black stripes running longitudinally down their back. While spotting an adult is easy, spotting a larva swimming in a raspberry is a bit harder and somewhat disconcerting if the raspberry is in your cereal.  Video credit: Maggie Lewis

Ah, but fruit flies are not all bad. The most famous fruit fly of all is, of course, Drosophila melanogaster. This tiny workhorse of scientific studies, a hero many of us met for the first time in high school biology, brought the 1933 Nobel Prize in Physiology or Medicine to Thomas Hunt Morgan for his pioneering work on mechanisms of heredity and the location of genes on chromosomes. Fruit flies have ventured to the International Space Station to help scientists study the effects of zero gravity on cardiac function and immune responses to disease. Closer to home and in my compost bin, they provide a vital ecological service by unlocking nutrients tied up in vegetable waste and returning these nutrients to food webs. So for good or bad, hail the tiny but mighty fruit fly.

On this unprecedented Thanksgiving in the time of COVID-19, Bug of the Week wishes you a happy one. Be sure to share some of your unwanted vegetables with ever-grateful fruit flies in your compost!

References

The wonderful video, images, and ideas for this week’s episode were created by doctoral candidate Maggie Lewis of the Department of Entomology, University of Maryland, College Park. We thank Ingalisa and Sahar Schrobsdorff for providing inspiration for this story and sharing an image of their clever fruit fly trap. The interesting references “Trapping spotted wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), with combinations of vinegar and wine, and acetic acid and ethanol” by P. J. Landolt, T. Adams, and H. Rogg, “Spotted Wing Drosophila: Potential Economic Impact of a Newly Established Pest” by M. Bolda, R. Goodhue, and F.  Zalom, “Effects of Interspecific Larval Competition on Developmental Parameters in Nutrient Sources Between Drosophila suzukii (Diptera: Drosophilidae) and Zaprionus indianus” by M. Edana Shrader, H. J. Burrack, and D. G. Pfeiffer, and “Flies, gnats, and midges” by W. A. Kolbe in “The Handbook of Pest Control” were used in preparing this Bug of the Week. To learn more about the African fig fly, please visit the following website:  https://academic.oup.com/jipm/article/10/1/20/5514212#136729274

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Some call it tupelo, others call it black or sour gum, but I call it drop-dead gorgeous, Nyssa sylvatica. Of all the trees in the forest, I think this one takes home first prize in autumn with shades of scarlet, orange, yellow, and green swirled together in a raucous mix. A common native of eastern North American forests, this beauty is almost pest free and thrives in managed landscapes.

One summer’s day while enjoying my Nyssa’s deep glossy leaves, I was miffed by several gnarly leaves at the tips of branches. Along the margins of said leaves were numerous yellowish-white crescent shaped galls. Galls are abnormal plant growths often associated with an insect, mite, nematode, or microbial pathogen. To get a closer look at this aberration, I plucked a few leaves and dissected the galls under the lens of a powerful microscope. The galls were hollow pockets packed with hordes of tiny yellow sucking insects known as phylloxerids, close kin to woolly aphids we met on beech trees and alder branches. These suckers are tiny, about a millimeter in length. Within each gall several of these gals were surrounded by dozens of pill-shaped translucent eggs, offspring produced asexually, without contributions from males.

How do they make galls? Well, galls form when an invading biotic agent, in this case a tiny insect, takes control of the genetic machinery of the undifferentiated cells in the developing leaf. Compounds released by the insect as it feeds tell the cells of the leaf something like this, “don’t expand to form a normal flat leaf, curl over along the margin and form a nice hollow pocket, a home where I can lay eggs and my children and I can dine unseen and unmolested by hungry predators.”  How clever is that! Pretty clever indeed, but one small problem exists. During autumn when my Nyssa drops its gnarly leaves, surely these leaf-bound gall-dwellers do not fare well in the soil. Where do the tiny phylloxerids go? 

Early in the season, marginal galls created the phylloxerid twist and distort young leaves at the tips of Nyssa’s branches. Within each gall are female phylloxerids laying dozens of pill-shaped eggs. Phylloxerids are strange looking creatures. Between the first set of legs in the center of the body are sucking mouthparts used to initiate gall formation and to remove sap from the leaf’s cells.

In a remarkable treatise on all things phylloxerid published some 116 years ago, Theo Pergande of Cornell University described the overwintering stages of the phylloxerid. He observed tiny wax covered phylloxerids in protected locations on the bark of the Nyssa. This week I scaled my Nyssa and several meters up in craggy folds along the trunk and in rough patches of bark were small white tufts of wax housing tiny sucking insects, presumably the overwintering generation of phylloxerids. While the exact molecular mechanisms by which gall-makers control their plant-hosts remain largely unknown, hundreds of species of insects and mites have discovered astonishing ways to alter the plants they live on and in during millions of years of intimate association.

Acknowledgements

We thank Drs. Fredericka Hamilton and Gary Miller of USDA for help in identifying the tiny creature featured in this episode. “North American Phylloxerinae Affecting Hicoria (Carya) and Other Trees” by Theo Pergande, and the amazing ‘Aphids on Worlds Plants’ website were used as references for this episode.

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Followers of Bug of the Week have witnessed the tale of spotted lanternfly unfold from its first discovery in Berks County, PA in 2014 to its spread across states lines, including Maryland’s border in 2018. With a recent sighting of euonymus leaf-notcher adults in Hampstead, MD less than 10 miles from the PA border, it looks like some of Maryland’s troubles may be heading Pennsylvania’s way. Let’s review how we got here. Back in 2002 a new pest was discovered in Fairfax, VA when a homeowner noticed a voracious caterpillar munching her ornamental euonymus. The caterpillars were sent to Eric Day at the Insect Identification Laboratory in Blacksburg, VA. Eric reared the larvae and sent the unknown moths to specialist John Brown at the Systematic Entomology Laboratory, USDA. Dr. Brown identified the moth as one not known to occur in the US – a new, exotic, invader. The scientific name of this alien is Pryeria sinica. Prior to its discovery in Fairfax, this pest was only known from eastern Russia and China through Korea, Japan, and Taiwan.  

In 2003 more moths were collected in Northern Virginia and on May 28, 2003 Gaye Williams at the Maryland Department of Agriculture identified specimens of Pryeria sinica from Anne Arundel County, Maryland. Somewhere along the way the new pest was dubbed the euonymus leaf-notcher due to the distinctive pattern of feeding caused by the caterpillar. As the large caterpillars eat, sections of leaf along the margin disappear down their gullets, hence the name leaf-notcher. The leaf-notcher passes winter as taupe colored eggs deposited in clusters of 150 or more on pencil-sized twigs near terminals of branches. Eggs hatch in mid-March and early April, and tiny caterpillars first feed in tight silken webs spun around unfolded leaves at terminals. As larvae grow, they move to expanded leaves to feed and are often found in large groups. Their presence is easily recognized by marginal notches and coarsely shredded leaves on the ground below. When abundant, these caterpillars can entirely strip shrubs.  

After completing development in early summer, larvae wander from the plants seeking protected locations to pupate. Large numbers of wandering caterpillars may alarm homeowners, but citizens should remain calm as caterpillars are not known to eat humans or pets. Caterpillars spin pupal cocoons amidst fallen leaves and adult moths appear in the autumn to fly, mate, and lay eggs on the terminals of euonymus branches. Unlike many moths, these are day fliers. They have unique patterns and colors on their body and wings that make them closely resemble wasps. The fact that they mimic wasps may help them avoid being eaten by day feeding predators such as birds. In North America, the leaf-notcher has been reported on Euonymus japonicus and E. kiautschovicus ‘Manhattan’. In its native range in Asia, the pest has been reported feeding on E. sieboldianus, E. japonicus, and E. alatus. Moreover, other members of the Celastraceae such as Celastrus punctatus and C. orbiculatus are recorded as hosts for this pest.

In early spring, euonymus leaf-notchers hatched from eggs and scores of caterpillars began to strip leaves of euonymus. After completing development in spring, caterpillars spun silken cocoons in protected locations. In late October and November, adult moths emerged from very cute pupae, mated, and deposited overwintering eggs on twigs of euonymus.

 The pest has two obvious weak points that provide excellent opportunities for management. From the time that egg laying ends in December until eggs hatch in spring, eggs can be crushed on the plant or simply removed by pruning off the terminal and disposing of it. If larvae are small or in restricted areas on a plant, then they too may be removed by a gloved hand or pruner. If larvae are widely distributed, abundant, or otherwise difficult to control manually, then several insecticides should perform well. Some of the most “environmentally friendly” insecticides for killing caterpillars contain Bacillus thuringiensis kurstaki (Btk) or the active ingredient called spinosad. Btk destroys cells in the gut of the caterpillar, a slow and painful death to be sure. Spinosad acts on the nervous system of the caterpillar, inducing a more rapid, twitchy form of death.   

Euonymus leaf notcher, where are you now? While no formal records are being kept at the present time by most state agencies, if you think you have spotted this pest you are always welcome to send an image to Bug of the Week care of Mike Raupp at [email protected]. Of course, you can also contact your state Department of Agriculture or University Extension Service and give them a heads-up. Happy leaf-notcher hunting!

Acknowledgements

 Many thanks to Charles Krause for sharing his wonderful images of euonymus leaf-notcher and providing the inspiration for this episode. Thanks also to Gaye Williams of the Maryland Department of Agriculture for confirming the identity of the adult moth.

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A few weeks ago, we visited a rockin’ orb weaving spider, the black and yellow garden spider, and watched it dispatch a dastardly brown marmorated stink bug. This week we meet another amazing orb weaver, the beautiful marbled orb-weaver. Usually in mid-autumn Bug of the Week begins to receive images of these fantastic predators and this year was no exception. I had the good fortune to bump into one of these beauties while wandering a trail along the Patuxent River in Columbia, MD. One look at the ornate coloration and patterns on the abdomen of this spider leave no doubt about how this beguiling spider got its name. The marbled orb-weaver is found throughout the contiguous lower 48 states and as far north as Alaska. It is also a common denizen of forests and fields in Europe.  

Like other members of its clan, the marbled orb-weaver spins a web of radial threads like the spokes of a wheel upon which spiral sticky capture-threads are placed. Capture-threads are remarkable evolutionary products of millions of years of bioengineering. Each capture-thread has a core of silk bearing scores of tiny droplets of viscous glycoproteins. These glycoproteins give the web its stickiness. Hapless insects that blunder into the web are trapped by the sticky silk until the spider zooms to its future meal, where it delivers a lethal paralyzing bite. The marbled orb-weaver has a clever strategy to capture prey while limiting exposure to its own enemies. After constructing its amazing web of death, the marbled orb-weaver hides in a retreat near the web. The retreat might be a cluster of dead leaves or a piece of loose bark. A strand of silk called a signal thread runs from the web to the retreat. When a potential victim is snared by the web, vibrations travel along the thread and alert the orb-weaver to the presence of its prey. The message is simple and clear – dinner is about to be served. 

Hiding in a folded leaf near its intricate web, a marbled orb-weaver awaits a victim. In a flash that even slow motion fails to capture, the orb-weaver descends to the center of the web to find its prey. Good fortune befalls a small wasp that strikes the web as it somehow manages to escape. Just to share what the orb-weaver might have done, I included a short clip to show how its cousin, the spotted orb-weaver, wraps up its prey.

Acknowledgements   

“The National Audubon Field Guide to North American Insects and Spiders”, by Lorus and Margery Milne, and “Estimating the Stickiness of Individual Adhesive Capture Threads in Spider Orb Webs”, by Brent D. Opell, were used as references for this episode. Bug of the Week gives special thanks to Frederic Zeldow for the nice picture of a marbled orb-weaver and inspiration for this episode.

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