Photo and information courtesy Buggy Joe Boggs from the Ohio State extension.
THE BOOGIE-WOOGIE APHID. Small colonies of beech blight aphids (Grylloprociphilus imbricator) are now appearing on their namesake host in southwest Ohio. These unusual aphids enshroud themselves in a profuse mass of white, wool-like filaments, and large numbers these "woolly aphids" will gather together in prominent colonies on twigs and branches of American beech trees. When a colony is disturbed, the aphids pulse their posterior ends in unison. This peculiar behavior has been accurately described as making the aphids look like "dancing dust balls doing the boogie-woogie."
Despite their nasty sounding name, these aphids cause little harm to their tree host. In fact, they have great entertainment value! However, they are prolific producers of sugary, sticky honeydew causing branches, sidewalks, parked cars, slow-moving gardeners, etc., beneath the colonies to become covered in sticky goo. Indeed, aphid colonies are often found by observing circular or semi-circular spots of sticky honeydew on hard surfaces beneath infested trees. The honeydew on leaves and branches may also become heavily colonized by black sooty molds. One of these molds (Scolias spongiosa) will only grow on honeydew from beech blight aphids. This unusual fungus grows as a dense, black, "fuzzy" mat on top of the honeydew on leaves. Over time, the black mat thickens into a furry mass. Then the fungus progresses into a growth phase that is unlike most sooty molds; it produces a spongy, golden-yellow heap that rises 1/2 " or more above the leaf or twig surface. The odd looking fungal growths look like nothing else that would commonly be associated with aphids or honeydew.
HOLEY THISTLE! Canada thistle (Cirsium arvense), with its spreading, invasive behavior, can present real problems to gardeners. However, this week I spotted a serious bio-ally that was introduced into the U.S. to help us fight this noxious weed. The thistle tortoise beetle (Cassida rubiginosa) feeds exclusively upon its namesake host and its damage to thistle plants can have a considerable impact. Over the past several years, I've watched a large patch of Canada thistle gradually decline due in large part to the depredations of the thistle tortoise beetle. Add the damage caused by other biological control agents such as the thistle head weevil (Rhinocyllus conicus) that attacks flower buds, and the bacterium Pseudomonas syringae pv. tagetis that bleaches out the terminal growth, and it makes me almost feel sorry for the poor thistle ... almost.
Thistle tortoise beetles damage plants both in the adult and the immature larval stages. Both feed as skeletonizers on the leaves of thistle. Feeding scars are irregular-shaped ovals with one leaf epidermis still intact producing what looks like a window pane. Most feeding occurs on the upper leaf surface. Eventually, the "window pane" drops out to produce holes. The collective feeding activity of the adults and larvae reduces the photosynthetic area of the thistle. This weed-whacking beetle is also known as the "thistle defoliating beetle" and it feeds on other non-native thistle nasties including musk (Carduus nutans) and plumeless (C. acanthoides) thistles.
The grayish-green oval-shaped larvae sport a pair of spike-like appendages (cerci) at the tip of their abdomen which are used to practice a bizarre behavior. They impale an odious collection of feces and shed exoskeletons with their cerci, and then they arch their abdomens upward to carry around their repugnant package umbrella-like over their bodies. They look like tiny, walking poo-balls. It is assumed this is a defense against predation.
CORRUGATED BIRCH LEAVES. The unusual leaf damage caused by the spiny witchhazel aphid (Hamamelistes spinosus) is now appearing on river birch in southern Ohio. The aphid is sometimes called the "river birch aphid" owing to its affinity for Betula nigra. This unusual aphid has a complex life cycle that involves two hosts: witchhazel (Hamamelis spp.) and birch (Betula spp.). On birch, the aphid produces raised ribs or "corrugations" on the upper leaf surface that match deep furrows between the veins on the lower leaf surface where the aphids live. The affected leaves will usually turn yellow and may prematurely fall off of the tree. On witchhazel, the aphids highjack leaf buds to produce a hollow green gall in which the aphids live. The gall is covered in short, green, flexible spines, thus the common name.
ROSESLUGGED LEAVES. The distinctive "windowpane effect" caused by the feeding activity of various members of the "roseslug sawfly complex" is just becoming evident on rose leaves in southwest Ohio. The possible culprits include the bristly roseslug sawfly (Cladius difformis), the common roseslug (Endelomyia aethiops), and the curled rose sawfly (Allantus cinctus). Early instar larvae of these sawflies feed as leaf skeletonizers on the lower or upper leaf surfaces, depending upon the species. The corresponding epidermis on the opposite side of leaf remains intact and eventually turns white producing the "windowpane" symptom. Later instars feed between the main veins producing "see-through" leaves. The bristly roseslug is a "season-long" pest with as many as six generations occurring in Ohio. The curled rose sawfly has two generations per season, and the roseslug only one generation. Control and prevention of damage depends on a proper identification of which roseslug culprit is responsible for causing the damage. Only the bristly roseslug continues to produce damage throughout the season. As their common name implies, the semi-transparent pale green larvae are covered with short bristles; however, the bristles are difficult to detect without magnification. Damage by this sawfly can be prevented by making a soil drench application of imidacloprid (e.g. Merit) or dinotefuran (e.g. Safari) at the time leaf buds start to break.
FOURLINED PLANT BUGS. Early damage on annuals and herbaceous perennials caused fourlined plant bug (Poecilocapsus lineatus) nymphs is just starting to appear in southern Ohio. This sucking insect feeds on over 250 herbaceous plant species including some woody ornamentals. The quick-moving nymphs are reddish-orange with black wing-pads. The appropriately named adults vary from yellow to green in color and have four black stripes down the wings. Like many plant-feeding Hemipterans, the fourlined plant bug injects enzymes into the plant causing cells to collapse. The bugs then feed on the resulting "slurry." The damage appears as small, round, black sunken spots which may coalesce into extensive blackened areas on infested leaves. The symptoms are commonly mistaken for a plant leaf disease. The plant bug has only one generation per year. However, both the adults and nymphs are heavy feeders and high populations can produce significant plant injury. Targeting the early instar nymphs for control reduces the overall damage caused by this insect, thus control measures need to be applied now to prevent much of the damage that will occur for the season.