Phomopsis Galls
At this time of year, when leaves are rapidly falling off deciduous trees, it is easy to spot clusters of woody galls on the branches and trunks of Bitternut Hickory, Red Oak and maple trees, among others. These abnormal, woody growths known as Phomopsis galls are caused by a fungus in the genus Phomopsis. They begin to form as patches of rough bark, and when fully formed they range from the size of a pea up to the size of a basketball.
Spores are produced by the fungus throughout the summer and are spread by wind and rain splashes. It is thought that spores infect a host by entering a wound in a young twig. The fungus then spreads to the branches and trunk. The galls do not kill the host tree, but can girdle small branches causing dieback. Many affected trees live for decades. (Photo: Bitternut Hickory tree infested with Phomopsis galls.)
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Female Sumac Gall Aphids Leaving Galls To Colonize Moss
The sac-like galls, often referred to as “Red Pouch Galls,” found on Staghorn and Smooth Sumac are anywhere from marble to ping pong ball-size, and usually become obvious in late summer and early fall when they often acquire a rosy pink blush. Inside the thin walls of these galls is one big hollow cavity, teeming with tiny orange woolly aphids (Melaphis rhois) referred to as Sumac Gall Aphids.
In the spring, female aphids lay an egg on the underside of a sumac leaf, causing the plant to form an abnormal growth, or gall, around the egg. The egg hatches and the aphid reproduces asexually within the gall. Thus, all the aphids inside the gall are identical clones of one another. In late summer or early fall, the winged females fly to patches of moss, where they establish asexually reproducing colonies. At some point these clonal colonies produce males and females which mate and it’s these mated females that fly off to lay eggs on sumac leaves in the spring.
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Oak Leaf Seed Galls Releasing Wasps
One of the most unusual looking insect galls, the Oak Leaf Seed Gall, is produced by a tiny gall wasp, Dryocosmus deciduus, on Black and Red Oaks. The leaves of these trees react to a wasp laying an egg on them by creating a unique swelling, or gall, around it. You can find clusters of up to 40 Oak Leaf Seed Galls at this time of year starting to burst open, releasing the adult wasps which have matured inside them.
Few records exist of galls, many of which are homes for developing young insects, being used as food for humans or for domestic animals but Oak Leaf Seed Galls, known as “black oak wheat” in Missouri and Arkansas, have been used to fatten cattle, sheep, pigs and chickens due to their high starch content.
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Oak Apple Galls
Galls are abnormal plant growths that are caused primarily by insects, but also by fungi, mites, nematodes and bacteria. Each gall insect has a specific plant host which produces a distinctive-looking gall. Of the 2,000 gall-producing insects in the United States, 1,500 of them are gall wasps or gall gnats. Of the over 800 different gall-makers on oaks, over 700 are gall wasps.
The pictured golf ball-size gall is referred to as an oak apple gall, specifically the Larger Empty Oak Apple Gall. (There are over 50 species of gall wasps that are known to produce oak apple galls in North America.) This particular gall is called “empty” due to the fact that the inner fibers disintegrate with age, leaving much of the interior empty. It housed the larva of a tiny gall wasp (Amphibolips quercusinanis) through the summer. An adult gall wasp laid an egg in a growing part of the plant (in this case a leaf bud) in the spring. The oak reacted to either a chemical secretion, the egg or the burrowing of the hatched larva (it is not known which of these agents is responsible) by forming a growth around it. This growth, or gall, provided the wasp larva with both shelter and food as the larva developed in a tiny chamber in the center of the gall. As the larva fed on the nutritious tissue in the walls of the chamber, it (the tissue) was constantly replenished by the oak tree. Eventually the larva pupated and the adult wasp, having emerged from its pupal case within the gall, chewed the tiny round exit hole you see in the gall before flying off to seek a mate.
As with the vast majority of plant galls, oak apple galls cause little harm to the overall health of their oak hosts.
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Elm Cockscomb Gall
Galls, abnormal plant growths caused by a variety of agents including insects, come in myriad sizes, shapes and colors. One of the most distinct is the Elm Cockscomb Gall which is caused by an aphid (Colopha compressa). These galls, named for their striking resemblance to a rooster’s comb, are maturing and turning red this time of year.
For much of the summer the aphids responsible for these galls live underground sucking sap from grass roots. In the fall a new (sexual) generation is born, takes to the air, mates and heads for an American Elm (Ulmus americana) tree where each female aphid lays a single egg under the bark. In the spring the emerging nymphs seek young American Elm leaves on which to feed. As they do so, the aphid nymphs emit compounds that result in the formation of galls. Each nymph matures inside a gall and then reproduces asexually, giving birth to hundreds of young within the gall. The mature, reproductive adult aphid dies and the young aphids develop into winged adults that exit the cockscomb gall through a slit on the undersurface of the leaf. These aphids then go down into the soil to feed on the sap of roots until the next generation is born.
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Cedar-Apple Rust Galls
Galls are abnormal plant growths caused by various agents including insects, mites, nematodes, fungi, bacteria and viruses. During the summer spores of a particular fungus cause the formation of brown Cedar-Apple Rust galls (Gymnosporangium juniperivirginianae) on Eastern Red Cedar trees. Members of the fungal family Pucciniaceae are known as rusts because the color of many is orange or reddish at some point in their life cycle.
This fungus requires two hosts, Eastern Red Cedar and primarily apples or crabapples, to complete its life cycle. The two host trees are usually located within a mile of each other. When the Cedar-Apple Rust galls on cedar trees get wet from spring rains, orange, spore-filled fingers or horns, called telia, emerge from pores in the gall. As the horns absorb water, they become jelly-like and swollen (see inset). When the jelly dries, the spores are carried by the wind to apple trees, where they cause a brownish mottling on apples, referred to as Cedar-Apple Rust, which makes apples difficult for growers to sell, even though it doesn’t affect the flavor or texture of infected apples. The rust produces spores on the underside of apple leaves in late summer, which, if they land on Eastern Red Cedar trees, cause galls to form, thereby continuing the cycle.
Spores produced on apple trees do not infect apple trees, only cedar; spores produced on cedar trees infect only apple trees. (Photo: Brown winter form of Cedar-Apple Rust gall & (inset) orange spring form of Cedar-Apple Rust gall. Blue “fruit” on Eastern Red Cedar branch is actually a cedar cone.)
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Blackberry Seed Gall
Galls, abnormal plants growths caused by many agents including insects, are formed during the growing season on the buds, leaves, roots and branches of plants as a response to chemicals or physical irritation. Many of these galls serve as shelters and a source of food for their developing inhabitants.
Blackberry is host to numerous gall-making insects, including mites, midges and gall wasps, and their temporary homes (galls) are most obvious in the winter. The Blackberry Seed Gall is caused by a tiny cynipid gall wasp, Diastrophus cuscutaeformis. A cluster of small, globular, seed-like galls within which the gall wasp larvae live are pressed together in a lump surrounding the cane. These galls derive their species name from their resemblance to dodder (Cuscuta) fruits. Each of these 1/10th-inch diameter chambers bears a spine, and together they create a reddish-brown hairy mass.
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Oak Leaf Galls
Galls are irregular plant growths which can be stimulated by the reaction between plant hormones and powerful growth regulating chemicals produced by some insects, mites, nematodes and fungi. Galls may occur on leaves, twigs, flowers, buds or roots. Many plants serve as gall hosts, but certain plant groups are more attractive to gall producers than others. The Oak family is by far the most popular (with 805 species of gall makers; the next largest family being the Daisy family, with less than 200 gall makers). Galls on oaks are most often caused by small wasps or midges.
Each gall-making species of insect produces a uniquely shaped and colored gall. Thus, it is possible to identify the insect within a gall just by noting the appearance of the gall itself as well as what plant it is on.The growth of the galls takes place in the spring. Gall-making insects lay eggs on the host plant, and the insect larva resides inside the gall that the plant forms. The galls provide the insects within them with both shelter and food. Because many oak leaves persist well into the winter, there is still the opportunity to find galls, though some may be lacking residents at this stage, as many insects emerge as adults in the fall after pupating within the galls.
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Hackberry Nipple Galls
If you look on the underside of the leaves of a Common Hackberry (Celtis occidentalis) tree at this time of year, you often find light-colored, raised bumps, commonly referred to as Hackberry Nipples Galls. The creatures responsible for these growths (through chemical interactions with the leaves) are a group of small insects called jumping lice, or psyllids, which resemble miniature (1/6 “ long) cicadas, with their large eyes and wings held roof-like over their backs.
Adult Hackberry psyllids emerge in September and October from the galls they have formed and seek shelter for the winter, often in the cracks and crevices of tree bark. Because they are attracted to lights and can often fit through the mesh of window screens, these insects also seek shelter in houses. Although considered a nuisance by some, Hackberry psyllids do not sting, nor do they carry disease. They pass the winter as adults and when they break dormancy in the spring, the psyllids exit houses, tree bark fissures, etc. and lay eggs on the emerging leaves of Hackberry trees. After the eggs hatch, the young psyllids start feeding, stimulating abnormal growth in the leaves, forming small pockets, or galls, surrounding the insects. The psyllids spend the rest of the summer sucking on tree sap safely within the protective galls before exiting in the fall. As a rule, these insects do not cause serious damage to their Hackberry tree hosts.
Blueberry Stem Galls
Up to a dozen tiny black wasps (Hemadas nubilipennis) will emerge from this gall in the spring, around the time when blueberry bushes are flowering. After mating, the female wasp lays her eggs under the surface of the blueberry stems. Once she has completed her egg-laying, she climbs to the tip of the shoot and repeatedly stabs it, preventing further growth.
The plant reacts to the wasp’s egg-laying by forming a kidney-shaped gall. The majority of galls (up to 70%) are formed on stems within the leaf litter. These galls can be up to an inch in diameter, and they contain many developing larvae that feed on the walls of the gall and grow during the summer, overwinter as larvae, pupate inside the gall in the spring, and then emerge as adults when the blueberry bushes are in bloom in late May and early June. The adults are almost entirely females.
If a blueberry bush has many galls, it can be problematic. A branch possessing a blueberry stem gall will not produce flower buds, and no flowers means no blueberries.
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Witch-hazel Cone Gall Aphids Laying Eggs
At this time of year there is a species of aphid, Hormaphis hamamelidis, that is laying eggs on Witch-hazel branches. Next spring female aphids will hatch out of these eggs and begin feeding on newly-emerged Witch-hazel leaves. The aphids inject the leaf with a substance that causes the leaf to form a cone-shaped growth, or gall, around the insect, providing it with both food and shelter. The galls are hollow, and have openings extending out through the leaves’ lower surfaces. Within the galls the unmated female aphids produce 50 – 70 young. Eventually the galls fill with winged female aphids which emerge through the cone openings, disperse, and repeat the process. The third generation of aphids consists of both males and females which mate and lay their eggs on Witch-hazel. The aphids that hatch from these eggs create the conical galls found on Witch-hazel leaves.
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Female Sumac Gall Aphids Leaving Galls & Heading For Moss
The sac-like galls found on Staghorn and Smooth Sumac are anywhere from marble- to ping pong ball-size, and usually become obvious in late summer when they often acquire a rosy pink blush. Inside the thin walls of these galls is one big hollow cavity, teeming with tiny orange woolly aphids (Melaphis rhois) referred to as Sumac Gall Aphids.
In the spring, female aphids lay an egg on the underside of a sumac leaf, causing the plant to form an abnormal growth, or gall, around the egg. The egg hatches and the aphid reproduces asexually within the gall. Thus, all the aphids inside the gall are identical clones of one another. In late summer or early fall, the winged females fly to patches of moss, where they establish asexually reproducing colonies. At some point these clonal colonies produce males and females which mate and it’s these mated females that fly off to lay eggs on sumac leaves in the spring.
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Goldenrod Ball Galls Provide Important Source of Winter Food for Downy Woodpeckers
A number of insects cause goldenrod plants to form galls – abnormal growths that house and feed larval insects. The Goldenrod Ball Gall is caused by a fly, Eurosta solidaginis. The fly lays an egg on the stem of a Canada Goldenrod (Solidago canadensis) plant in early spring, the egg hatches and the larva burrows its way into the stem; the plant reacts by forming a gall around the larva. The larva overwinters inside the gall, pupates in late winter and emerges in early spring as an adult fly. Prior to pupating, the larva chews an exit tunnel to, but not through, the outermost layer of gall tissue. (As an adult fly it will not have chewing mouthparts so it is necessary to do this work while in the larval stage.)
Downy Woodpeckers (and Black-capped Chickadees) have discovered this abundant source of winter food, and dine on the larva after chiseling a hole into the gall. Downy Woodpeckers tend to make a tidy,narrow, conical hole by pecking, while Black-capped Chickadees tend to make a messy, large, irregular hole by grabbing bits of the gall with their bill and tugging them free. While woodpeckers prefer larger galls that are located high on goldenrod plants growing near wooded areas, these are not the only factors taken into consideration.
A woodpecker extracts the fly larva through the tunnel the larva excavates prior to pupating, as this facilitates rapid removal of the larva. Downy Woodpeckers can determine whether or not a gall has an exit tunnel, and if it doesn’t, they usually abandon the gall without drilling into it. The likelihood of smaller parasitic wasp larvae occupying the gall (and a plump fly larva not being present) is much greater if there is no exit tunnel, and these smaller prey apparently are not always worth the woodpecker’s time or energy.
NB: Correction: this week’s Mystery Photo was of a Gray Birch (Betula populifolia) bract, not a Paper, or White, Birch (Betula papyrifera) bract. While similar, there are differences between these two species of birch that I should have recognized (especially when looking at the leaf!). Thanks to Kathy, an alert blog reader, who caught this error.
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Black Cherry – well known to most readers!
Black Cherry, more than most tree species, often has several identifying features even after it loses its leaves. The buds of Black Cherry have about ten scales, each of which is brown at the tip and green at the base. The bark of young Black Cherry trees is typically smooth, reddish in color and covered with grayish, horizontal lines called lenticels — small openings that allow the passage of gases in and out of the tree. The bark on older Black Cherry trees consists of squarish scales, curved outward at their vertical edges, somewhat resembling burnt potato chips. Black Cherry is one of several trees on which the fungus Apiosporina morbosa causes Black Knot Galls. Lastly, Black Cherry is the primary host for the Eastern Tent Caterpillar moth. These moths encircle Black Cherry branches with their egg masses, and the eggs hatch just as Black Cherry’s leaves emerge from their buds, providing food for the young larvae.
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Gall-making Mites on Sugar Maple Leaves
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Within a week or two of unfurling, Sugar Maple leaves are attacked and consumed by all kinds of creatures, some of which are insects and mites that cause the leaves to develop abnormal growths called galls. Certain species of eriophyid mites form felt, or erineum, galls, often on Silver and Sugar Maple leaves. After spending the winter months under the scales of buds, these mites emerge in the spring when leaves appear, move out onto the surface of the leaves and begin to feed. Their feeding induces the growth of thousands of tightly-packed leaf hairs which provide shelter for the mites on the leaf surface. These hairs appear as bright pink or red patches that resemble felt. The mites, too small to even be seen with a hand lens, move to the inside of these structures for the rest of the growing season.
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Woolly Oak Leaf Gall
Of the 2,000 kinds of galls found on North American plants, 800 different kinds form on oaks. One of these is the woolly oak leaf gall, produced by a tiny Cynipid wasp, Callirhytis lanata. This gall is usually attached to the mid-vein on the underside of an oak leaf, and looks like a ball of wool. It may be as large as three-fourths of an inch and is often bright pink or yellow in color, fading to light brown in the fall. Oak trees have lots of tannic acid in them (a defense which makes the tree unpalatable to herbivores), with the highest concentration found in oak galls. (The bitter taste is where the name “gall” originated.) It’s possible, since tannins are somewhat anti-microbial, high-tannin galls such as the woolly oak leaf gall may protect the larva against fungi and bacteria.
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Mossy Rose Gall Wasp Larvae Cease Feeding
In the spring, the 4mm-long cynipid gall wasp, Diplolepis rosae, lays up to 60 eggs (through parthenogenesis) inside the leaf bud of a rose bush. A week later, the eggs hatch and the larvae begin feeding on the leaf bud. This stimulates the abnormal growth of plant tissue, and a Mossy Rose Gall, covered with a dense mass of sticky branched filaments, is formed. The gall provides the larvae with food and shelter through the summer. In late October, when the Mossy Rose Gall is at its most colorful, the larvae stop eating and pass into the prepupal stage, in which they overwinter inside the gall. In February or March, the prepupae undergo a final molt and become pupae. If the pupae aren’t extracted and eaten by a bird during the winter or parasitized by another insect, adult wasps exit the gall in the spring and begin the cycle all over again.
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Winged Female Woolly Aphids Leaving Sumac Leaf Galls
The sac-like galls found on Staghorn and Smooth Sumac are anywhere from marble- to ping pong ball-size, and usually become obvious in late summer when they often acquire a rosy pink blush. Inside the thin walls of these galls is one big hollow cavity, teeming with tiny orange woolly aphids (Melaphis rhois). In the spring, female aphids lay an egg on the underside of a sumac leaf, causing the plant to form an abnormal growth, or gall. A number of parthenogenic generations are produced inside the gall, and then in late summer or early fall, the winged females fly to patches of moss, where they establish asexually reproducing colonies. According to biologist D.N.Hebert, these colonies produce the males and sexual females responsible for recolonizing sumac each spring.
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Goldenrod Bunch Gall
Galls are abnormal plant growths that are caused by a number of agents, including insects. Each gall-making insect has a specific host plant and location (leaf, stem, bud) on which it lays its eggs in the spring, during the growing season. The egg-laying and/or hatching and chewing of the larva causes the plant to react by forming a growth around the insect. Galls of different species of insects vary in their shape and the gall maker can often be identified as a result of this.
Goldenrods are host to about 50 species of gall-making insects, two-thirds of which are midges, or tiny flies. Goldenrod Bunch Galls, also called Rosette Galls, are the result of an egg being laid in the topmost leaf bud of Canada Goldenrod, Solidago canadensis by a midge in the genus Rhopalomyia, often Rhopalomyia solidaginis. The stem of the goldenrod stops growing, but the leaves don’t. The resulting rosette of leaves provides shelter and food for the midge larva, as well as a host of other insects, including other midges. Adult Goldenrod Bunch Gall midges emerge from the galls in the fall, and females lay eggs in the soil. The larvae hatch within one to two weeks and spend the winter underground, emerging in the spring to start the cycle all over again. Interestingly, Rhopalomyia solidaginis lays all male or all female eggs, one or the other.
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Blackberry Seed Gall
Galls, abnormal plants growths caused by many agents including insects, are formed during the growing season on the buds, leaves, roots and branches of plants as a response to chemicals or physical irritation. These galls serve as shelters and a source of food for their inhabitants. Blackberry is host to numerous gall-making insects, including mites, midges and gall wasps, and their temporary homes (galls) are more obvious now that Blackberries have lost their leaves. The Blackberry Seed Gall is caused by a cynipid gall wasp, Diastrophus cuscutaeformis. This wasp gets its species name from the resemblance of the galls it forms to the fruit of Dodder or Cuscuta, a parasitic plant. A cluster of small, globular, seed-like galls within which the gall wasp larvae live are pressed together in a lump surrounding the cane. Each of these 1/10th-inch diameter chambers bears a spine, and together they create a reddish-brown hairy mass.
Willow Beaked-Gall Midge
Now that most of the leaves have fallen, it’s a good time to look for galls that form on woody plants. Willows are host to a great number of gall-making insects, including tiny flies called midges. The most common species of willow gall midge is the Willow Beaked-Gall Midge, Rabdophaga rididae. In the spring, after mating, the adult female midge lays an egg in a willow bud (often terminal) that is just starting to expand. The egg soon hatches and the larva burrows deeper into the bud, which causes the bud tissue to swell and form a gall, usually with a “beak” at the top. The larva remains inside the gall through the winter, where it has a constant supply of food (the interior of the gall) and shelter. In the spring the larva pupates, and an adult midge emerges and begins the cycle all over again. Some gall midges are crop pests, but willows are not significantly damaged by the Willow Beaked-Ball Midge.
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Jewelweed Gall Midges
Abnormal plant growths called galls come in all sizes and shapes, are found on leaves, buds and stems, and are caused by a number of agents, including insects. A majority of insect galls are caused by the eggs and developing larvae of flies, wasps and midges. Jewelweed, or Touch-Me-Not (Impatiens capensis), has a very distinctive looking aborted bud gall that is produced by a midge (Schizomyia impatientis). While some galls provide shelter and food for a lone resident, the Jewelweed Gall Midge is colonial, and several orange larvae can be found residing in separate cavities within the gall. These midge larvae are now emerging and will overwinter as adults.
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Spiny Witch Hazel Galls
Aphids are responsible for the formation of two different galls (abnormal plant growths caused by insects, fungi, bacteria and viruses) on Witch Hazel (Hamamelis virginiana). A cone-shaped gall forms on leaves and a second type of gall covered with spiny points grows from branches. The latter gall, referred to as the Spiny Witch Hazel Gall, provides many aphids (Hamamelistes spinosus) with both food and shelter while they are developing inside the gall. (Their two-year life cycle involves birches as their next host.) The pictured Spiny Witch Hazel Gall has split open enough to allow ants to discover and have access to the aphids. Once the ants enter the gall, they stroke the resident aphids with their antennae, stimulating the aphids into producing droplets of tasty “honeydew” from the tips of their abdomens, which the ants find irresistible. In return, the ants protect the aphids from predators.
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Blueberry Stem Gall
If you happen to notice a ¾” to 1 ¼”- long, brown kidney-bean-shaped or round structure on a blueberry bush this time of year, you’ve come upon the blueberry stem gall – a summer and winter home for a dozen or so wasp larvae that will pupate and emerge in the spring as very small (less than 1/8”) black wasps (Hemadas nubilipennis). Last summer a female wasp laid her eggs in a tender, developing blueberry shoot. She then climbed to the tip of the shoot and stabbed it repeatedly, causing considerable damage. Within two weeks the eggs hatched, and the larvae began feeding, which, along with the egg-laying, stimulated the formation of the gall. Initially a blueberry stem gall is green and spongy; by fall it turns red, and by late autumn, it is brown and woody. Next summer, look for multiple holes in these galls that were chewed by the exiting wasps.
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