Joseph F. Boggs, David J. Shetlar, Jane C. Martin, Pamela J. Bennett, James A. Chatfield, and Gary Y. Gao
Damaging infestations of mimosa webworm (Hyphantria cunea) and the common bagworm (Thyridopteryx ephemeraeformis) occurred this season in various areas of Ohio, with bagworm populations being primarily concentrated in southern and central Ohio. Sawfly populations remained low throughout much of the state with the exception of dogwood sawfly (Macrem-phytus tarsatus), redheaded pine sawfly (Neodiprion lecontei), and the scarlet oak sawfly (Caliroa quercuscoccineae). Heavy infestations of locust leafminer (Odontota dorsalis) caused very noticable damage to black locust, particularly in the southern part of Ohio, and lilac leaf miner (Gracillaria syringella) produced damage to Japanese tree lilacs in southeastern Ohio. Adults of several species of conifer bark beetles emerged at the same time that some areas of the state were experiencing severe moisture deficits, fueling speculation that dry conditions could have made conifers more susceptible to attack. Numerous species of eriophyid mites were observed this season, but various rust mites and a 'rosette mite' (Trisetacus gemmavitians), caused the greatest concern. Japanese beetle (Popillia japonica) adults were present for an extended period of time; however, most late fall larvae had reached the normal third instar overwintering stage. Bluegrass billbug (Sphenophorus parvulus) and chinch bug (Blissus leucopterus) populations were high this season, especially in southern and central Ohio.
Insect and mite activities reported in 1998 in Ohio State University Extension's Buckeye Yard and Garden Line (BYGL) and Pest Evaluation and Suppression Techniques (PEST) newsletters as well as other sources are summarized and compared to previous seasons. Unusual insect and mite activity is also reported.
Despite its common name, fall webworms (Hyphantria cunea) generally appear in Ohio sometime in early July. However, this season, the first generation made an unusually early arrival with eggs hatching in northeastern Ohio in mid-June. There are two generations in Ohio, but eggs typically hatch over an extended period of time, producing considerable generational overlap. Larvae of both generations cause the same damage, by feeding on leaves shroud-ed in webbing, but unless limited by disease and/or beneficial insects, the nests produced by the second generation are generally more numerous and conspicuous compared to those produced by the first generation.
High populations occurred in localized areas throughout much of Ohio; however, beneficial insects appear to have had an impact on some of those populations. In 1997, Dan Herms (Ohio State University Department of Entomology) reported heavy infestations near Wooster, Ohio, but larvae randomly collected from those populations were heavily parasitized (5). This season, Herms noted that webworm populations were greatly reduced in those same geographical areas.
The unsightly nests of mimosa webworm (Homadaula anisocentra) were again on prominent display on honeylocust in Ohio this season; however, unlike last year, populations seemed more evenly distributed throughout the state rather than being concentrated mostly in southern Ohio (5). Larvae of this moth skeletonize the lower leaf surface as they feed within 'nests' consisting of webs spun over the foliage. Normally, two to three generations occur in Ohio, with each generation overlapping so that larvae are present at all times. This occurs because females lay eggs in the nests produced by the previous generation.
Female mimosa webworm moths were first observed in northeastern Ohio in late May, and the resulting first-generation nests were abundant and very noticeable by mid-to-late June throughout Ohio. First instar larvae of the second generation were found in nests in early August. Last season, a distinct third generation was noted because of an unusual break in activity that lasted from mid- August to early September (5). This year, no such pause was observed, and although a third generation occurred, it was not easily discernable from the second generation.
Two unusual nest-making caterpillars made their debut this season in the pages of BYGL. Both the ailanthus webworm (Atteva punctella) and the redbud leaffolder (Fascista cercerisella) were observed late in the season causing damage to their respective namesakes in southwestern Ohio. The redbud leaffolder is so named because the larvae typically create nests by folding over leaf edges. They may also 'stick' two leaves together. Thick bundles of silk arranged along the leaf edges give the appearance that the leaves or folds are stitched together. The larvae feed within these nests as skele-tonizers and consume the epidermis of both the upper and lower leaf surfaces. The caterpillars have reddish-brown head capsules and alternating black and light green bands running the length of their body. They pupate to become a medium-sized velvety-black moth.
Ailanthus webworms are the immature stage of an ermine moth. The larvae produce nests on the tree of heaven (Ailanthus altissima) by pulling two to three leaflets around a network of loose webbing. The larvae then consume the leaflets. The caterpillars have a wide, light greenish-brown stripe down their backs and several thin, alternating white and olive-green stripes along their sides. They are sparsely covered with short, erect hairs, which help to suspend the caterpillars within the webbing. When disturbed, the caterpillars move backwards out of the nest and drop towards the ground on a strand of silk. Several larvae may be found per nest. Although ailanthus webworms are capable of defoliating their odoriferous namesake, such damage is rare, and the insect is usually of little consequence.
The common bagworm, Thyridopteryx ephemeraeformis, once again developed damaging populations in many areas of Ohio this season. This insect has been on the rise each year in Ohio since the severe winter of 1993-1994 significantly reduced its occurrence (3). As was observed last year, the distribution of this bagworm remains highly variable between the northern and southern parts of the state, with the southern portion tending to have higher populations (5). One difference between the 1997 and 1998 season was that a greater number of damage reports involved deciduous trees. These observations were a reminder that the insect has a wide host range and has been found feeding on more than 128 different species of plants.
The grass bagworm, Eurukuttarus confederata, was very evident in southern and central Ohio this season. As its common name implies, this bagworm feeds exclusively on grasses and constructs its bag from parallel bundles of its host plant. Bags produced by early instars are green but later become brown as the grass stems and blades attached to the bag become dry. This turf-dwelling caterpillar emerges and completes its development much sooner than its arboreal cousin, and this may cause some confusion with identification. When the relatively small bags produced by this bagworm begin to appear on vertical surfaces rising above the ground (e.g., tree trunks, fence posts, and more) in mid- to late June, landscapers may incorrectly conclude that they are seeing a second generation of the common bagworm. Of course, both bagworms only have a single generation each year. Unlike the common bagworm, the grass bagworm causes little damage, and infestations seldom warrant control efforts.
In past years, gregarious feeding caterpillars such as the yellownecked caterpillar (Datana ministra), walnut caterpillar (D. integerrima), and the hickory tussock moth (Lophocampa caryae) were common, and some sporadic outbreaks were observed (1, 3, 4). However, this season, these caterpillars were conspicuous because of their relative absence from the landscaping.
Conversely, large solitary-feeding caterpillars, such as the four- to six-inch-long hickory horned devil (regal or royal walnut moth, Citheronia regalis), the tomato hornworm (five-spotted hawk moth, Manduca quinquemaculata), and the parsleyworm (black swallowtail butterfly, Popilio polyxenes), were once again a common sight. The catalpa hornworm (catalpa Sphinx moth, Ceratomia catalpae) was particularly noticeable, with high populations being reported throughout Ohio. Natural control agents for this insect were also very evident. For example, the white, oblong cocoons of one of the parasitic wasps responsible for reducing populations of this insect were observed 'blossoming' from second generation horned worms in late August in Wooster, Ohio.
Large numbers of white cocoons played a role in disclosing high populations of oak skeletonizer (Bucculatrix ainsliella) in northeastern Ohio. In late June, the yellowish-green larvae of the first generation of this moth began pupating. When these caterpillars are ready to pupate, they drop down on silken threads and attach their white, longitudinally ridged cocoons to just about any surface found in the landscape.
Despite their diminutive size, thousands of these cocoons plastered on lawn chairs, plants, screens, houses, napping gardeners, and other surfaces, may be a real nuisance, and there are two to three generations per year. Although early instars feed as leaf miners and later instars feed on the lower leaf surface as skeletonizers, larval-feeding activity seldom causes significant injury. Spray applications are generally not recommended, since the pesticides may kill parasitic wasps that target the cocoons and reduce caterpillar populations.
A number of sawfly defoliators caused considerable localized damage this season. These included: dogwood sawfly (Macrem-phytus tarsatus), redheaded pine sawfly (Neodiprion lecontei), and the scarlet oak sawfly (Caliroa quercuscoccineae). Dogwood sawfly caused damage to native gray dogwood, and the redheaded pine sawfly produced serious defoliation of Scotch pines in several Christmas tree plantations, primarily in southwestern Ohio.
The slug-like, black to dark-green scarlet oak sawfly caused heavy damage to pin oaks in southeastern Ohio. The larvae feed gregariously and skeletonize the lower leaf surface, leaving behind the upper epidermis. Adults damage leaves by inserting their saw-like ovipositor into the upper leaf surface and cutting rows of small pockets for eggs along major leaf veins. There are two to three generations per year. This insect feeds on pin oak and occasionally eastern black oak as well as its namesake, scarlet oak.
Several sawflies with malevolent reputations, based on past histories of causing damage in Ohio, had relatively low populations this season (1, 2, 3). These defoliators included: the early season European pine sawfly (N. sertifier), introduced pine sawfly (Diprion similis), azalea sawfly (Amauro-nematus azaleae), dusky birch sawfly (Croesus latitarsus), mountain-ash sawfly (Pristiphora geniculata), and the late-season white pine sawfly (N. pinetum). Little widespread damage caused by these sawflies was observed this season.
Adults of three leaf-mining sawflies in the genus Fenusa were on the wing in northeastern Ohio in late April. These included: birch leaf miner (F. pusilla); elm leaf miner (F. ulmi); and European alder leaf miner (F. dohrnii). At the same time, larval mining activity of the hawthorn leaf-mining sawfly (Profenusa canadensis) commenced in southwestern Ohio.
Larvae of these sawflies mine the leaf parenchyma, producing large blister-like, reddish-brown "blotch" mines, which usually extend from the leaf margin toward the midvein. In previous years, all four of these insects caused substantial injury to their hosts in various areas in Ohio. For example, in southwestern Ohio in 1997, the elm leaf miner produced heavy localized defoliation (5). However, with the exception of some heavy, highly localized infestations of hawthorn leaf miner, populations of these insects were relatively low this year.
The annual ravaging of black locust leaves by locust leaf miner (Odontota dorsalis) occurred this season throughout much of Ohio (3,5). The digitate blotch mines produced by the larvae coupled with the skele-tonized leaves produced by the adult beetles caused many trees to become completely brown by late summer.
The lilac leaf-miner (Gracillaria syringella) caused considerable damage to Japanese tree lilacs in southeastern Ohio. Early instar larvae of this tiny moth feed gregariously in blotch-like mines. Leaf-mining activity typically causes the leaves to pucker or curl along the edge of the mines and may cause leaves to drop. Mined portions of attached leaves eventually dry up and become unsightly. Later instar larvae abandon the mines and roll or web together several leaves on which they feed. There are two generations per year, and they may also infest black ash, privet, and euonymus.
There are numerous species of conifer bark beetles in Ohio. All are in the family, Scolytidae, and most belong to one of two genera, either Dendroctonus or Ips. These beetles burrow into the bark, lay eggs, and the larvae tunnel in and feed on phloem tissue. Their activity produces characteristic 'shotholes' in the bark, making an infested tree look as though it has been peppered with shotgun pellets. Although conifer bark beetles are serious primary pests in many parts of the United States, the species found in Ohio are generally secondary pests, meaning that they prefer to colonize stressed trees.
Weakened conifers cannot defend themselves, because they lack the ability to produce enough sap or gum to "pitch-out" borers trying to enter through the bark. Generally, when trees are under attack by bark beetles, it means they are in serious trouble, usually because of an accumulation of stress-inducing factors (e.g., root decline, moisture stress, and more). Several conifer bark-beetle species emerged in late July in many areas of Ohio. At the same time, many areas of Ohio were in the early stages of a serious moisture deficit. BYGLers speculated that the dry conditions may have predisposed some conifers to attack by the opportunistic bark beetles. Given that colonized trees were most likely already in a state of serious decline, it was noted that trees riddled with conifer-bark-beetle holes cannot be 'saved' using an insecticide approach. The proper treatment for such infested trees is 'basal pruning' (removal).
Adult-emergence dates for several clear-winged moth borers were reported for northeastern Ohio as follows: the first ash/lilac borer (Podosesia syringae) adults were captured in pheromone traps on May 5; the first lesser peachtree borer (Synanthedon pictipes) on May 6; and the first peachtree borer (Synanthedon exitiosa) on June 12. Bronze birch borer (Agrilus anxius) adults began their emergence around May 21.
Damage caused by the buckeye/horsechestnut petiole borer, Proteoteras aesculuana, began appearing on buckeyes along the Little Miami River in southwestern Ohio in early April. Larvae of the moth bore into leaf petioles, causing the new leaves to turn black and droop. Infested leaves usually remain attached to the tree and give the appearance of having been damaged by frost or freeze injury. Coupled with the occurrence of a severe freeze in the area in late March, the symptoms presented a diagnostic challenge. However, the presence of the borer could be disclosed by looking for a small hole in the petiole.
The maple petiole borer (Caulocampus acericaulis) produced similar damage on maples in central Ohio. This sawfly also causes leaves to discolor and droop; however, larval feeding activity usually causes the leaves to detach. Thus, the main symptom is an accumulation of fallen leaves, which have a short section of petiole attached, with the end usually blackened and shriveled. Adults lay eggs on petioles in May. As the larvae tunnel and feed, the petiole is weakened; the leaves then drop to the ground. The borer is left in the petiole section still on the tree; later the borer drops to the ground and pupates. This insect creates concern but does not typically damage trees, so control is usually not needed.
The lace bug "season" was initiated by reports in late April of hawthorn lace bug (Corythucha cydoniae) adults leaving overwintering sites and being found on the underside of cotoneaster leaves in northeastern Ohio. By mid-May, high populations of this insect were reported on hawthorns in southern Ohio. Along with attacking its namesake and cotoneaster, the hawthorn lace bug may also be found on pyracantha, flowering quince, crabapple, mountain-ash, and shadbush.
By mid-July, a number of other lace bugs had been observed. These included sycamore lace bug (Corythuca ciliata); oak lace bug (C. arcuata) on burr oak; and walnut lace bug (C. juglandis). In late August, azalea lace bug (Stephanitis pyriodes) and rhododendron lace bug (S. rhododendri) were reported to be ravaging their namesakes.
Lace bugs produce characteristic symptoms that include the appearance of numerous small, yellow or whitish spots or stippling on the upper leaf surface. The stippling is caused by the insects' feeding activity on the underside of the leaves. Another symptom is the occurrence of copious deposits of black, varnish-like excrement on the underside of leaves. The lace bugs observed this season caused considerable damage. In particular, the oak lace bug was singled out as producing very noticeable yellowing of leaves of white oaks in central Ohio and burr oak in the southwestern part of the state. The damage was intensified as the result of a late season production of eggs, which spawned an additional generation in late August.
Eriophyid mites were by far the most prevalent group of mites found in Ohio landscapes this season. In essence, the 1998 season was a repeat of last season (5) with the following mites being found in great abundance -- the leaf-epidermis-rupturing pearleaf blister mite (Phytoptus pyri) on callery pear; Vasates aceriscrumena causing finger-like "spindle galls" on the upper leaf surface of sugar maple; V. quadripedes producing globose, pouch-like "bladder galls" on the upper leaf surfaces of red and silver maples; Phytoptus tiliae producing "nail galls," or elongated growths with pointed tips, on the upper leaf surface of linden; Aculops toxicophagus spawning puckered, irregular, wart-like galls on the lower and upper leaf surfaces of poison ivy; Eriophyes caulis generating pubescent, reddish-brown leaf petiole galls on walnut; Eriophytes tiliae producing light green, felt-like erineum galls on little leaf linden; and Acalitus fagerinea creating green- to yellowish-brown erineum galls on American beech.
However, despite their relative abundance, the aforementioned eriophyids seldom caused enough damage to warrant control efforts. Such was not the case for several other eriophyid mites observed this season.
Rust mites feed by rupturing cells on the surface of plant foliage. Their feeding activity can cause appreciable injury, and damaging populations of three species were observed in several locations in Ohio.
The bronzing effects of baldcypress rust mite (Epitrimerus taxodii) were noted in the southern, central, and northeastern parts of the state. The hemlock rust mite (Nalepella tsugifolia), which causes hemlock foliage to turn blue-green, then reddish-brown, and Nalepella halourga (no common name), which causes bronzing of the inner needles of Colorado blue spruce, were observed in southern and central Ohio.
These eriophyid rust mites behave as "cool season" mites, and high populations were generally observed during cool months, especially in the fall.
One of the most damaging species of eriophyid mite, the "rosette mite" (Trisetacus gemmavitians), was found to be active on Scotch pine in several Christmas tree plantations in central and southern Ohio. Although this mite has no common name, it is called the "rosette mite" because it induces the formation of a peculiar rosette-like gall.
According to the USDA, Agriculture Handbook No. 573, titled, An Illustrated Guide to Plant Abnormalities Caused by Eriophyid Mites in North America, "each rosette consists of a cluster of aborted buds or stunted needles. Typically, the shoots become infested, and the elongation of growing points is inhibited. Numerous buds are clustered at the tip, and the needles that develop from these buds are stunted."
Early-season pesticide application, targeting the rosette mite prior to gall formation, is a recommended control approach; however, results are seldom satisfactory since there is a very narrow application window, and timing dates vary from year to year. The alternative recommendation is to prune and destroy infested rosettes. Of course, this may severely disfigure the tree and limit its value in Christmas tree production.
Although the relatively mild 1997-1998 winter was conducive to continual activity of the cool-season spruce spider mite (Oligonychus ununguis), this mite never reached the expected high populations and associated levels of damage during the spring in most areas of the state. As with 1995 and 1996, large numbers of mites appeared to have been washed from their hosts by heavy spring rains (3, 4). However, populations did recover in the fall, and damage from this resurgence is predicted to be apparent next spring.
The prolonged hot, dry weather over much of Ohio through mid-summer and into early fall proved favorable to the development of high populations of several warm-season mites. Damaging populations of two-spotted spider mite (Tetranychus urticae) were observed on a number of landscape plants, including roses and burningbush euonymus. The oak spider mite (Oligonychus bicolor) was also common in Ohio this season. Coupled with damage caused by oak lace bug, entire trees had canopies dominated by "washed-out" leaves.
Several insect observations made this season were considered unusual. For example, in late-June, the fuzzy, white, flocculent material produced by immature plant hoppers began to show up on the distal stems of numerous species of herbaceous perennials and woody ornamentals. Populations throughout Ohio seemed high, and most were concentrated on plants near the ground, making the insects very apparent to home gardeners and landscapers. Although plant hoppers suck plant juices and produce copious quantities of honeydew, they caused relatively little damage. At most, the cottony fluff may reduce the aesthetic appeal of infested plants, but the problem was short-lived. Once the immatures completed their development, the flocculent material easily washed off.
Cockscombgalls or pod galls were observed forming along the midveins on the underside of hawthorn leaves in southwestern Ohio in late April. Each gall contained three to five tiny midge fly larvae. As the season progressed and the galls matured, they became raised, bumpy, and changed from light green to deep red, making them look like a cockscomb. One or more galls were found per leaf, and as they developed, leaf expansion was restricted, causing the leaves to become severely twisted or curled. However, populations appeared to be low, and no significant injury was suspected.
As with the 1997 season, the 1998 season produced some interesting developments regarding white grub-producing beetles (5). May/June beetle (Phyllophaga spp.) adults appeared a little ahead of schedule, bouncing off windows and window screens and shattering the evening calm in early May. Despite their common name, green June beetles (Cotinis nitida) arrived within their "normal" calendar-date window. The big, metallic-green beetles emerged en masse and began cruising lawns in southern Ohio, terrorizing backyard gardeners, sunbathers, small pets, and others in late July.
Japanese beetles (Popillia japonica) were somewhat unpredictable this season. In Ohio, adults normally emerge from the last week of June through July, and most eggs are laid by mid-August. Once eggs hatch, larvae usually feed and develop to the overwintering third instar stage. Last year, adults emerged over an extended period of time, and the subsequent egg production also occurred over a long period of time. As a result, a high percentage of larvae overwintered in the second instar stage (5).
This year, it first appeared that Japanese beetles would repeat this atypical life cycle. Adults began to appear in southern and central Ohio landscapes in early June and continued to remain on the scene through July, August, and September. This seemed to indicate that Japanese beetle populations were remaining asynchronous in terms of developmental stages, and a percentage of the populations would go through the winter in the second instar larval stage rather than third instars, the usual overwintering stage in Ohio.
However, by October, most Japanese beetle grubs were in the third instar stage. Speculation on how this developmental realignment occurred centered on the dry conditions experienced over much of Ohio from August through October. The beetle lays dehydrated eggs, which must absorb water from the environment. Without water, the eggs fail to mature and they die. It was theorized that eggs laid late in the season failed to produce the expected late developing larvae that would be overwintering this year in the second instar stage.
Bluegrass billbug (Sphenophorus parvulus) made a dramatic "comeback" in Ohio this season. This insect has been almost nonexistent for a number of years. Populations were high throughout the state, with heavy damage occurring in late June; however, the problem was often misdiagnosed as drought injury. Chinch bug (Blissus leucopterus) populations also rebounded from a number of "down" years, with lawns in southwestern Ohio showing severe browning from feeding by this insect in late July and August.
The "usual suspects" once again appeared on Ohio doorsteps, seeking entry points for overwintering. These included gnat-like hackberry psyllids (Pachypsylla celtidismamma), boxelder bugs (Boisea trivittatus), and multicolored Asian lady beetles (Harmonia axyridis). In September and October, masses of Asian lady beetles collecting on the outside walls of Ohio homes were one of the most common subjects of telephone calls to Extension offices.
Ground bees also accounted for telephone calls regarding nuisance problems. Several species of ground bees create nests by burrowing in the ground. These ground bees are also called mining bees or digger bees. Unlike honey bees, ground bees are solitary and do not form social colonies. However, nests may be close together when soil conditions are suitable, and these collective gatherings are sometimes referred to as "colonies" although there is no caste system involving "workers" and a common queen. Instead, each burrow is constructed by an individual female.
Burrows vary between species of ground bees, but most are about one-quarter inch or smaller in diameter and are surrounded by a mound of loose soil, which may rise to a level of one to two inches above the ground. Ground bees are not aggressive and seldom sting. Several species of ground bees are important pollinators, while others provision their burrows with insects and are important biological control agents; thus control is generally not recommended unless a serious threat is perceived.
1. Chatfield, J. A., J. B. Boggs, P. Kauffman, D. J. Shetlar, N. Taylor, and R. H. Zondag. 1993-94. Ornamental Plant Problems in Ohio: 1993. Ornamental Plants. Special Circular 142. Ohio Agricultural Research and Development Center. The Ohio State University. pp. 28-31.
2. Chatfield, J. A., D. J. Shetlar, N. Taylor, J. F. Boggs, P. J. Bennett, R. H. Zondag, M. A. Ellis, and A. Baumgard. 1993-94. Ornamental Plant Problems in Ohio: 1994. Ornamental Plants. Special Circular 142. Ohio Agricultural Research and Development Center. The Ohio State University. pp. 24-27.
3. Boggs, J. F., D. J. Shetlar, G. Y. Gao, D. Balser, D. C. Caldwell, R. H. Zondag, and J. A. Chatfield. 1995. Plant Insect Pest Problems in Ohio: 1995. Ornamental Plants: Annual Reports and Research Summaries. Special Circular 152. Ohio Agricultural Research and Development Center. The Ohio State University. pp. 38-41.
4. Boggs, J. F., D. J. Shetlar, J. A. Martin, P. J. Bennett, J. A. Chatfield, D. R. Balser, and G. Y. Gao. 1996. Insect and Mite Activity Noted in Ohio: 1996. Ornamental Plants and Research Reviews. Special Circular 154. Ohio Agricultural Research and Development Center. The Ohio State University. pp. 17-22.
5. Boggs, J. F., D. J. Shetlar, J. C. Martin, P. J. Bennett, J. A. Chatfield, G. Y. Gao, and C. Carlson. Insect and Mite Activity Noted in Ohio Nurseries and Landscapes: 1997. Ornamental Plants: Annual Reports and Research Reviews. Special Circular 157. Ohio Agricultural Research and Development Center. The Ohio State University. pp. 18-25.