Walnut Twig Beetle, Thousand Cankers Disease

Distribution  |  ID & Biology  |  Hosts & Habitats  |  Impacts  |  Prevention & Control

Background

The walnut twig beetle, Pityophthorus juglandis, is a tiny Scolytid bark beetle native to the southwestern US. It is the insect vector of Thousand Cankers Disease. The disease, first observed in the 1990s but not recognized until 2008, has killed many walnut trees planted outside their native range across the western US.  It is now a serious threat to walnuts in their native eastern range.

Distribution

The walnut twig beetle was first detected in the Eastern US in 2010 and has now been found in Tennessee, Virginia, Pennsylvania, North Carolina, Ohio, and Maryland. It is widespread across Western US. While not yet in New York, the walnut twig beetle has been confirmed in adjacent states and poses a threat to walnuts in New York, the Northeast and New England.

 

Map Source: ThousandCankers.com

 

Identification and Biology

The walnut twig beetle is reddish brown to brown and only 1.5-2mm long. Identification of this tiny bark beetle is possible with a dissecting microscope but confirmation by an expert is recommended because there are many similar species.  A very good identification guide is “LaBonte and Rabaglia, A Screening Aid for the Identification of the Walnut Twig Beetle, Pityophthorus juglandis Blackman.” The fungus is carried into the tree on the bodies of adult beetles; the beetles bore under the bark, create tunnels or galleries, and lay their eggs.

 

Steven Valley, Oregon Department of Agriculture, Bugwood.org
Steven Valley, Oregon Department of Agriculture, Bugwood.org

Hosts and Habitats

All walnut species tested so far are susceptible, particularly black walnut but also the Northern and Southern California black walnut species.

Impacts

Thousand Cankers Disease, caused by a fungus and spread by the walnut twig beetle, is usually lethal to walnut trees (Juglans spp), particularly black walnuts (Juglans nigra), within a few years of noticeable symptoms. Black walnut has high economic value for wood production. Throughout its native range, the net volume of black walnut growing stock on timber land was valued at over $500 billion.

 

Evidence of Thousand Cankers Disease. Ned Tisserat, Colorado State University, Bugwood.org
Tree Killed by Thousand Cankers Disease.  Karen Snover-Clift, Cornell University, Bugwood.org

Prevention and Control

Prevention through quarantine is key because symptoms (thinning canopy, leaf yellowing/wilt, tip die-back) appear after it is too late to save infected trees or nearby trees.  Most eastern states where the disease has been detected have adopted quarantines on the movement of nursery walnuts and walnut wood. Maps of range and quarantine information can be found here.

Heat treatment of logs before movement for processing has been shown to be an effective way to prevent spread of both the disease and beetle.

Pheromone baited traps have been developed for beetle detection in new areas but are only effective at short range.

Sirex Woodwasp

Sirex Woodwasp, European Woodwasp, European Horntail

 

Problem | History and Range | Identification | Biology | Signs and Symptoms | Damage in New York | Damage in the rest of the US | Management and Control | New York Distribution Map

Problem

Female Sirex woodwasp Gyorgy Csoka, Hungary Forest Research Institute, Bugwood.org

Sirex Woodwasp, Sirex noctilio, larvae are woodborers that tunnel deep into the trunks of all species of pine (Pinus) trees. As the female Sirex woodwasp, Sirex noctilio, prepares to lay her eggs, she secrets a toxic mucus and symbiotic fungus into the tree which work synergistically to weaken, and in some cases kill the attacked tree(s).  The mucus creates a suitable environment for the fungus which decays the wood so it is easier for the larva to digest.

Sirex woodwasp has caused mortality of millions of North American pines planted In Southern Hemisphere forests, where Sirex Woodwasp (S. noctilio) is also an invasive species. Currently, Sirex woodwasp is estimated to cause between $16 and $60 million in annual damages per year in those forests.

In the US, southern and western native pine forests and plantations face both an economic and ecological threat with the potential loss of valuable pine stands. The USDA Forest Service estimates the Sirex woodwasp could cost between $2.8 and $17 billion in lost sawtimber and pulpwood values if it becomes a nationwide established species.

History and Range

The Sirex woodwasp, S. noctilio, is native to Europe, Asia and north Africa. It was first discovered in North America in 2004 in a trap in Fulton, NY (Oswego County). In its native habitat it is considered a secondary or minor pest. Where it has been introduced it is considered to be a major pest. In its native range S. noctilio attacks Scots (P. sylvestris) Austrian (P. nigra) and maritime (P. pinaster) pines and is known to attack North American pines including red (P. resinosa), loblolly (P. taeda), slash (P. ellotti), ponderosa (P. ponderosa), lodgepole (P. contorta) and Monterey (P. radiata). White pine (P. strobus) is also attacked but is less preferred.

Pines 6” and larger are susceptible, stressed, suppressed and crowded pines seem to be favored. It is thought that the Sirex woodwasp can spread approximately 25 miles per year.

Sirex woodwasp known range, as of 2011. USDA/APHIS/PPQ
World Distribution of Sirex noctilio, 2000. Dennis Haugen, Bugwood.org

 

Identification

Female and Male Sirex Woodwasp Vicky Klasmer, Instituto Nacional de Tecnologia Agropecuaria, Bugwood.org

Adult Sirex woodwasp’s head and thorax are blue-black and have black antennae. Females have a blue-black abdomen with orange legs, while the abdomen of males has an orange mid-section and they have black hind legs. Woodwasps are 1 to 1.5 inches long and lack the typical narrow “waist” that most other wasps and hymenoptera have and there is a pointed plate that projects from the end of the abdomen.

There are many native woodwasps (Siricid woodwasps), and it is recommended to have a suspect woodwasp identified by an expert. Our native woodwasps only feed on dead and dying trees, while the Sirex woodwasp can also attack healthy trees. Images and descriptions of many Siricid woodwasps can be found in the Canadian Journal of Arthropod Identification “Siricidae (Hymenoptera: Symphyta: Siricoidea) of the Western Hemisphere” at http://www.biology.ualberta.ca/bsc/ejournal/sgsbws_21/sgsbws_21.html.

Larvae are 0.04 to 1 inch long, are creamy white and legless and have a spine at the end of their abdomen which is diagnostic for all woodwasps (also called horntails).

Larva – Vicky Klasmer, Instituto Nacional de Tecnologia Agropecuaria, Bugwood.org

Biology

The female Sirex woodwasp injects her ovipositor into the trunk of a pine tree, just into the wood, and injects one egg at a time along with the symbiotic fungus, Amylostereum areolatum, and a toxic mucus. The toxic mucus suppresses the tree’s defenses and decreases the tree’s ability to protect itself from the wood decaying fungus. When the larva hatches, it feeds on the fungus decayed wood and enzymes, and possibly the fungus as well, as it bores through the wood. Females lay 25 to 400 eggs. Fertilized eggs become females and unfertilized eggs become males. Larvae feed in the tree for 10-11 months and then pupate near the bark. Adults emerge after three weeks. Peak adult emergence is in July, but can occur from July through September. There is believed to be one generation per year in New York.

Many of the specifics of Sirex woodwasp biology and the relationship between Sirex and the fungus are still unknown. Research is currently being conducted that will hopefully provide more detail on this fascinating insect and its associated toxic mucus and symbiotic fungus.

Signs and Symptoms

Infested trees initially wilt, needles droop, then change from green to light green to red. This usually takes 3-6 months. Wilted trees generally die within a year.

When adults emerge they bore a 1/8 to 3/8 inch round exit hole through the bark. Trees in newly infested areas have exit holes 10-30 feet above ground. In heavily infested areas, the whole trunk is utilized by the larvae and exit holes can be seen along its length. There may be lines of pitch or resin beads at oviposition (egg laying) sites.

In the wood, frass packed larval galleries tunnel in towards the heartwood and then loop back out towards the bark. The fungus causes a brownish stain in the outer sapwood.

Wilted needles – Dennis Haugen, Bugwood.org
Exit holes – Dennis Haugen, Bugwood.org
Pitch from oviposition sites – Dennis Haugen, Bugwood.org
Staining caused by Amylosetereum fungus – Dennis Haugen, Bugwood.org

 

Damage in New York

Damage and galleries – Vicky Klasmer, Instituto Nacional de Tecnologia Agropecuaria, Bugwood.org

In New York State the largest damage is being seen in plantation Scots, Austrian, and red pine. These plantations were planted in the early to mid-20th century and were often unmanaged and are now crowded, stressed and underperforming. The death of these underperforming trees is not having a large economic or environmental effect in New York.

Damage in the rest of the US

Whereas Sirex woodwasp damage in New York is not profound, Sirex Woodwasp damage has the potential to be much greater in the South and Pacific Northwest. The projected economic damage to these forests is upwards of $17 billion dollars with hundreds of thousands of trees lost.

To see maps of the potential damage to US pines click here. http://www.fs.fed.us/foresthealth/technology/invasives_sirexnoctilio_riskmaps.shtml

Management and Control

Biological control using a parasitic nematode, Deladenus siricidicola, has been successful in some infestations. The nematode infects the woodwasp larvae and ultimately sterilizes the females. These females lay infertile eggs that are instead filled with nematodes. As nematode populations grow, they can keep Sirex Woodwasp populations below damaging levels. Easy to rear in the lab, Deladenus siricidicola can be injected into infested trees. For more information about the lifecycle of Deladenus siricidicola see Cornell University’s Biological Control website:  https://biocontrol.entomology.cornell.edu/pathogens/Deladenus.php

There are also parasitoid wasps, many native to North American, which could assist in managing Sirex woodwasp populations.

New York Distribution Map

This map shows confirmed observations (green points) submitted to the NYS Invasive Species Database. Absence of data does not necessarily mean absence of the species at that site, but that it has not been reported there. For more information, please visit iMapInvasives.

European Crane Fly

OriginHabitatIntroduction and SpreadImpactsIdentificationPrevention and ControlNY OccurrencesOther Occurrences

Background

European crane flies (Tipula paludosa), also known as leather jackets during the larval stage, are an invasive insect that have become established in the northwestern United States, eastern Canada, and New York.  Crane flies look like large mosquitoes, but exploit a different ecological niche and do not bite humans.  Crane flies are most problematic to the turf grass industry, especially on golf courses. This is because the flies lay their eggs in the soil for larvae to feed. Tipula paludosa as well as Tipula oleracea are exotic European crane flies that are present in New York.

Adult European crane fly. Photo: Canadian Forest Service Archive, Canadian Forest Service, Bugwood.org

Origin

European crane flies (T. paludosa) are native to northwestern Europe.

Habitat

European crane flies thrive in moist soils and prefer mild winters and cool summers.  In Quebec, Canada, T. paludosa had higher larval abundance in silt or clay soils rather than sandy soils (Taschereau et al. 2009). They have been found in many different types of turf grass (at homes and golf courses), sod farms, and grass fields.  The flies also favor areas with thatch buildup.

Introduction and Spread

European crane flies were most likely introduced through the transport of infested materials.  During the summer months, T. paludosa larvae will reside below the soil surface and pupate.  By end of August or early September, the adults emerge, mate, and lay 200-300 eggs within 24 hours.  Once the eggs hatch, the larvae will feed throughout the fall and spring.  T. paludosa complete one generation per year and T. oleracea will complete two generations per year with adults emerging in the spring in addition to the fall.  T. oleracea females are better fliers, which could contribute to their eggs being more dispersed than T. paludosa eggs (Peck 2006).

Impacts

European crane flies have a large impact on the turf grass industry.  The larvae may scalp lawns during foliar feeding and damage the root systems as well.  Dawson et al. (2004) found that larvae of crane flies significantly impact shoot and root biomass and the microbial composition of the soil. Damaged lawns may appear yellow or have bare spots.  Crane fly larvae have the potential to affect cereals and produce crops, nursery stocks, bare root and container stock, and flowers as well.  The highest damage intensity from T. paludosa has been observed in late spring.  Additionally, some natural predators, such as birds and skunks, may disrupt lawns when foraging for larvae in the grass.  Natural predators feeding on larvae and swarms of mature adult crane flies maybe become nuisance species for home owners.

European crany fly adult on ground foliage.  Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

Identification

European crane flies are about a half-inch long, with six long legs.  A distinguishing characteristic of adult European crane flies is a dark-colored band on the leading edge of the wing next to a light colored band.  The rest of the wing has no pigmented areas, which is useful for distinguishing them apart from some native species.  Eggs of European crane flies are black and oval shaped and can be found near the soil surface.  The larvae are gray-brown and worm-like.  Larvae have a tough skin with visible veins.  The empty pupal cases may be seen in low turf and look like small grey-black twigs.

Wing of adult T. paludosa.  Photo: John Sankey, web.ncf.ca/bf250/gardendip.html

Prevention and Control

Monitoring:  Surveying for crane fly larvae should be performed in the early spring by observing turf damage.  To survey, take core samples or turn over the top 1-2 inches of sod in one square foot plots and count the larvae.  Pouring warm water with dish soap on a mowed plot will also make the larvae emerge if you prefer not to dig the sod up; however, this method may not be as successful.  In the fall, surveying for the pupal cases can be performed in low cut grass.  In the fall, adults should be noticeable especially in large infestations. Since T. paludosa adults do not fly far, the surrounding areas should be surveyed for eggs and larvae in the current and future years.  If you are unsure if you are looking at an invasive European crane fly, collect samples and take them in to your local Cornell University Cooperative Extension office or send them to a specialist or diagnostic lab.

Manual and Mechanical Control: Maintaining proper turf grass health may help to allow the grass to recover from damage faster.  Applying  fertilizers in the fall will help maintain turf quality.  Increasing soil aeration and dethatching in the spring may help reduce crane fly populations.  Also, because larvae thrive in moist soils, timing of irrigation may be critical during the oviposition stage of the lifecycle and throughout the fall season.  Draining soils during the critical period of the life cycle may be beneficial to reduce fly populations in infested soils.  Eggs that are laid at the soil surface and the larvae that emerge can be raked up and destroyed to prevent future damage from occurring.

Biological Controls:  Crane flies have some natural predators, such as various species of birds or microorganisms.  Beauveria bassiana is a fungus that has been seen to attack crane flies. Nematodes applied in the spring have been effective in some areas as well (mainly the Northwestern United States) in 55 degree temperatures and irrigated soil.  For some fly populations, manual and biological control methods are environmentally preferred.

Chemical Controls:  Chemical controls for crane flies are most effective if applied in the fall during the egg laying period, but may be used in the spring as well.  Imidacloprid, trichlorfon, carbaryl and chlorpyrifos are effective against crane flies. Contact your local extension office for more information on chemical pesticides and always read the instructions on the labels.  For more information on potential lawn and turf solutions:
http://www.northeastipm.org/schools/outside/low-maintenance-turf/
http://www.organiclandcare.net/store/nofa-organic-lawn-and-turf-handbook

To prevent additional spread of crane flies, movement of sod, container stock, and other turf grass materials should be limited.

New York Occurrences

European crane flies (Tipula Paludosa) were first detected in New York State in 2004.  This species has been found in Erie, Monroe and Niagara counties in New York and is most prevalent in the western half of the Erie Canal corridor.  A similar species of crane fly, Tipula oleracea, is also present in Monroe, Niagara, Ontario, Onondaga, Oswego, Seneca, Wayne, Nassau and Suffolk counties in New York.

Other Occurrences

T. paludosa has been documented in the Northwestern United States, New York and Eastern Canada.

Asian Longhorned Beetle

Biology        Hosts        Impacts

Introduction

The Asian longhorned beetle (Anoplophora glabripennis) is a wood-boring beetle believed to have been introduced into the U.S. on wood pallets and wood packing material in cargo shipments from Asia (the beetle’s native range includes China and Korea). Asian longhorned beetle (ALB) larvae bore through wood of a wide variety of hardwood species, most notibly maples, elm, horsechestnut, willow, sycamore and birch. ALB boring phsycially weakens the trees and disrupts sap flow. Branches with boring damage are more likely to break off, creating a public saftey hazard. Trees will eventually be killed by ALB boring damage.

Asian long-horned beetle adult – Kenneth R. Law, USDA APHIS PPQ, Bugwood.org

ALB was first discovered in the US in 1996 on several hardwood trees in Brooklyn, NY. Additional infestations were found in Long Island, Manhattan and Queens. In 1998, the beetle was discovered in Chicago, IL. Asian Longhorned beetles were later found in Jersey City, NJ, in 2002 and in Middlesex and Union counties, NJ, in 2004. In 2007 the insect’s NYC range was found to extend to Staten Island and Prall’s Island in the Hudson River. To our north, the beetle was discovered in Toronto, Canada, in 2003. In 2008, a large number of Asian longhorned beetles were discovered in and around Worcester, MA in urban and rural forests. In 2011, ALB was found in Tate Township Ohio.

Asian long-horned beetle historic and current NY infestations (USDA APHIS 2014)
2014 ALB Brooklyn, Manhattan, and Queens historic and current infestations (USDA APHIS 2014)
2014 ALB Central Long Island quaranteen area (USDA APHIS 2014)

To view maps of all current quarantine and infestation zones visit the USDA APHIS ALB Page.

 

Asian long-horned beetle adults with dime and exit holes – Kenneth R. Law, USDA APHIS PPQ, Bugwood.org

Biology

Asian longhorned beetle adults can reach 1½ inch in length with very long antennae (reaching up to twice the length of the insect’s body). The beetle is shiny black with small, irregular white markings on its body and antennae. Adult Asian longhorned beetles are active during the summer and early-autumn months. After mating, females deposit their eggs in depressions chewed into the bark of hardwood trees (females can lay 35 to 90 eggs in a season). After hatching (typically 10-15 days), beetle larvae feed by tunneling under the tree bark into the cambium (fresh sapwood) for several weeks. The larvae then tunnel into the xylem (heartwood) were they feed through the winter, forming galleries in the trunk and branches of infested trees. Adult beetles chew their way out through round holes approximately 3/8 inch in diameter, emerging from June through October (presence of the adult emergence can often be detected from sawdust around and beneath these holes, and by sap oozing from the holes).

 

Hosts

Asian longhorned beetles prefer such hardwood trees as: red maple (Acer rubrum), sugar maple (Acer saccharum), boxelder (Acer negundo), Norway maple (Acer plantanoindes), sycamore maple (Acer pseudoplatanus),  silver maple (Acer saccharinum),  horsechestnut (Aesculus hippocastanum), willows (Salix spp.), and American elm (Ulmus Americana). They will also attack birches (Betula spp.) and sycamores (Platanus spp.).

 

Impacts

Asian longhorned beetle gallery development and exit holes weaken the integrity of infested trees and can eventually result in death of severely infested trees. It is theorized that if the beetle spreads beyond its current North American range, millions of acres of hardwoods could be killed, potentially causing more damage than the combined impact of Dutch elm disease, chestnut blight, and gypsy moths. National and State forests, parks,and private backyards could be impacted, as could such forest dependent industries as lumber, maple syrup, house and furniture manufacturing, and commercial horticulture nursery stock.

 

Asian long-horned beetle larva and damage – Steven Katovich, USDA Forest Service, Bugwood.org

Swede Midge

Introduction

The Swede midge (Contarinia nasturtii), an invasive agricultural pest (also known as the cabbage crowngall fly and cabbage gall midge) was first detected in New York in 2004 in Niagara County. Although the insect is a native of Europe and southwestern Asia, it is believed the midge was introduced into NY from the Canadian province of Ontario where it was first found on broccoli in 1996. By the end of 2007, the Swede midge had been confirmed in 12 NY counties (Allegany, Chenango, Franklin, Herkimer, Jefferson, Livingston, Onondaga, Otsego, Rensselaer, Steuben, Suffolk, and Yates).

Biology

This species is a small (1.5 – 2 mm), light brown fly that is indistinguishable from many other midges except by an expert entomologist. Adult midges emerge in the spring from pupae that have over-wintered in the soil. Adult flies mate soon after and females search for suitable host plants. Each female can lay about 100 eggs during their one to five day lifespan. The females lay their eggs on the growing point of young plants. Larvae hatch from the eggs after a few days and begin to feed in groups on the growing plant tissue. Larvae complete their development in 7 – 21 days after which they drop to the ground and pupate in the soil. Adults can emerge within two weeks, restarting the cycle. Depending on temperature and length of growing season, there can be up to five overlapping generations of Swede midge per year.

 

Damage

As they feed, Swede midge larvae produce a secretion that breaks down the surface of the growing point of the plant and liquefies the cell contents, resulting the formation of leaf and flower galls and a misshapen growing point. Damage caused by Swede midge larvae feeding results in distorted growing tips and may produce multiple (or no) growing tips; young leaves may become swollen or crumpled and leaf petioles or stems may exhibit brown scarring. Swede midges feed only on cruciferous vegetable crops, such as cabbage, cauliflower, broccoli, and Brussels sprouts, frequently causing severe losses. The insect also damages canola, collard, horseradish, kale, mustard, rutabaga, turnip, and radish.

Swede midge damage

Management

Insecticides can be used to kill adults or prevent them from laying viable eggs. However, controlling larvae is much more difficult because insecticide would have to enter the plant tissue upon which the larvae are feeding. Currently, the best way to manage Swede midge damage is to limit the spread of the insect into new areas. Adults are very weak fliers, so the primary vector of introduction is believed to be the movement of transplants which may contain eggs or larvae, or movement of soil which may contain pupae. Repeated working of infested soil can reduce the number of viable pupae. Also, because adult Swede midges cannot travel far, crop rotation using noncruciferous plants can help to reduce the likelihood of spreading an infestation.

Hemlock Woolly Adelgid


Origin & Spread  |  Biology  |  Impacts  |  Detection  |  Management | New York Distribution Map

Introduction

The hemlock woolly adelgid (HWA, Adelges tsugae) is an aphid-like, invasive insect that poses a serious threat to forest and ornamental hemlock trees (Tsuga spp.) in eastern North America. HWA are most easily recognized by the white “woolly” masses of wax, about half the size of a cotton swab, produced by females in late winter. These fuzzy white masses are readily visible at the base of hemlock needles attached to twigs and persist throughout the year, even long after the adults are dead.

Here’s a handy Hemlock Woolly Adelgid ID video from UMass Amherst:

 

Origin and Spread

Hemlock woolly adelgid is native to Japan and possibly China where it is considered a common inhabitant of both forest and ornamental hemlock and spruce trees. It rarely achieves pest outbreak densities or inflicts significant damage to host trees in its native Asian habitat because natural enemies and host plant resistance help keep HWA populations in check.

Hemlock woolly adelgid was first detected on the east coast of North America in Richmond, Virginia, in the mid-1950s (Souto et al. 1995). Since its likely accidental introduction from southern Japan (Havill et al. 2006), HWA has spread to 18 eastern states from Georgia to Maine, devastating populations of native eastern (Tsuga canadensis) and Carolina (T. caroliniana) hemlock. HWA now covers nearly half the range of native hemlocks and appears to be spreading about 10 miles a year. It has reached its southern limit, but continues to expand its range to the west and north.

HWA was first detected in New York State in the early 1980s (Souto et al. 1995). Outbreaks have expanded from initial infestations on Long Island and in the Hudson Valley to the Rochester area, the Catskill Mountains, and recently into the Finger Lakes region.

HWA was first detected on the west coast of North America in British Columbia in the 1920s, and now also has a range from northern California to southeastern Alaska. There, it occurs on both mountain hemlock (Tsuga mertensiana) and western hemlock (T. heterophylla) trees. However, HWA does not cause extensive mortality or damage on West Coast hemlocks. Recent comparative genetic analyses suggest that populations in the Pacific Northwest may actually be endemic to that region or originated from very early introductions.

Biology

The hemlock woolly adelgid has a complex life cycle, involving two different tree host species as well as asexual and sexual life stages. On eastern hemlock, HWA produces two generations a year, an overwintering generation (sistens) and a spring generation (progrediens); these two generations overlap in the spring. The progrediens has two forms, a wingless form that remains on the hemlock and a winged form (sexuparae) that flies in search of a suitable host spruce tree upon which to start a sexual reproductive cycle (McClure 1995). In New York, there are no suitable spruce, thus the winged HWA are not successful. Each generation has six stages of development: egg, four juvenile (nymph) stages, and the adult.

Hemlock woolly adelgid annual life cycle on hemlock in North America. (From Cheah et al. 2004)

Overwintering adult females are black, oval, and soft-bodied (approximately 2mm long). They are usually concealed under the white woolly masses of wax (ovisacs) they secrete from special glands on their back-side. From March through May, these females lay 50 to 300 eggs in the woolly masses. The eggs are brownish-orange and very small (0.25mm long by 0.15mm wide). Depending on spring temperatures, eggs hatch from April – June.                                         

 Adult female HWA with woolly ovisacs and eggs
HWA with woolly ovisacs and eggs
Adult female HWA, wax removed
Adult female HWA, wax removed
Hemlock woolly adelgid nymph in the crawler stage
Hemlock woolly adelgid nymph in the crawler stage


Newly hatched nymphs – also known as crawlers – are reddish-brown with a small white fringe near the front (less than 0.5mm long). Crawlers search for suitable sites to settle, usually at the base of the hemlock needles, where they begin to feed and will remain attached to the tree with their specialized sucking mouthparts for the rest of their lives. Crawlers, an important dispersal phase of HWA on hemlocks, can be spread by wind, on the feet of birds, or in the fur of small mammals (McClure 1990). Once settled, these HWA crawlers quickly develop through the four nymph life stages, and mature in June.

Some of the adults of the spring generation (progrediens) are wingless and remain on the hemlock tree, feeding and producing eggs protected by woolly masses just like the overwintering generation, but during June-July. Their offspring hatch into crawlers, quickly settle onto hemlock branches, begin to feed and then enter a dormant period for several months until late October when feeding and development resumes. These nymphs become the next overwintering generation (sistens). The other portion of spring adults has wings and leaves the hemlock trees in June in search of spruce trees to complete the sexual phase of HWA reproduction. However, in North America, no spruce species (Picea spp.) are suitable hosts and any offspring produced die within a few days of feeding. Thus, the winged adult form can be a significant source for HWA population reduction. This is particularly important considering the number of winged adults produced in the spring generation increases with the density of overwintering adelgids, likely a result of changes in nutritional quality in the hemlock host tree.

Impacts

The hemlock woolly adelgid feeds deep within plant tissues by inserting its long sucking mouthparts (stylets) into the underside of the base of hemlock tree needles. It taps directly into the tree’s food storage cells, not the sap. The tree responds by walling off the wound created by the insertion of the stylets. This disrupts the flow of nutrients to the needles and eventually leads to the death of the needles and twigs. Needles will dry out and lose color, turning gray and eventually dropping from the tree. Terminal buds will also die resulting in little to no new shoot growth. Dieback of major limbs can occur within two years and generally progresses from the bottom of the tree upward (McClure et al 2001).

The hemlock woolly adelgid has an impressive reproductive potential: consider that one female in the winter generation produces an average of 200 eggs which in turn mature and each female of this adult spring generation produces on average another 200 eggs each. That’s 40,000 eggs in one year, starting from one individual female! Thus, HWA populations can grow rapidly in a relatively short period of time. Heavy HWA infestations, particularly in the southern Appalachian Mountains, can kill hemlock trees in as little as four years, with older trees dying more quickly. However, for reasons still under investigation, some infested trees in parts of New England survive for 10 years or more.

HWA damage to needles and branches after 2-3 years of infestation
HWA damage to needles and branches after 2-3 years of infestation
Decline and mortality in infested hemlock in North Carolina

 

HWA infestation resulting in thinning of hemlock crown
HWA infestation resulting in thinning of hemlock crown

Eastern hemlocks play a unique ecological role in eastern forests. Long-lived and shade tolerant, hemlocks may grow in single-species stands or in combination with deciduous hardwood species. They are frequently found growing on exposed slopes as well as protected gorges and stream bottoms. Eastern hemlocks create a cool, damp and shaded microclimate that supports unique terrestrial plant communities, maintains cool stream water temperatures for fish and stream salamanders, and provides important winter habitat structure and food resources for wildlife. Research, particularly in the hard-hit southern hemlock forests, has indicated that declines in hemlock from HWA can result in losses of unique plant and animal assemblages and drastic changes to ecosystem processes (Ellison et al. 2005).

Climate change, particularly warmer summer temperatures, will affect the suitability of habitat for eastern hemlock in the Northeast. Perhaps more troublesome are projected increases in overwintering temperatures that may promote the range expansion of HWA into more northern hemlock forests, areas previously considered unsuitable for HWA survival (Paradis et al. 2008).

Light infestation of hemlock woolly adelgid
Light infestation of hemlock woolly adelgid
Heavy infestation of hemlock woolly adelgid
Heavy infestation of hemlock woolly adelgid

Detection

Detecting new HWA infestations at the leading edge of its range is critically important for slowing the spread of HWA. Unfortunately, HWA is difficult to detect at low population levels. The first signs of HWA are the presence of the white, woolly ovisacs on the underside of twigs, most often on the newest growth. This white, waxy wool is most easy to observe with the naked eye or through binoculars January through June. Other signs of infestation include graying and dropped needles and limb dieback.

Winter is the optimal time to detect HWA, as the ovisacs are most apparent and the leaves from adjacent deciduous trees that could interfere with observations are absent. An inexperienced observer may confuse several look-alikes with HWA. Spider sacs may look superficially similar but are constructed of much stronger fibers and are usually not closely pressed to hemlock twigs. Spittlebugs, never found in the winter, produce watery, white foam, not wooly and waxy fibers. Scale insects are common, but are found directly on the hemlock needles, not the twigs. Pine pitch and bird droppings may also confuse an untrained observer.

Hemlock woolly adelgid look-alikes that may confuse untrained observers
Hemlock woolly adelgid look-alikes that may confuse untrained observers

 

For more information about examining hemlock trees and surveying hemlock stands, please see Whitmore (2009) “Early Detection of the Hemlock Woolly Adelgid (Adelges tsugae) in Small Northeastern Hemlock (Tsuga canadensis) Woodlots

Management

Sasajiscymnus tsugae adult feeding on HWA eggs
Sasajiscymnus tsugae adult feeding on HWA eggs

Currently, the two approaches for managing HWA infestations are chemical insecticides and the use of natural enemy predator species as biological control.

Infested hemlock trees can be protected individually with chemical, systemic insecticides. These insecticides, typically applied as a soil drench or an injection into the soil below the organic layer or as a basal bark spray, are incorporated by sap flow into the tree’s tissues and can provide multiple years of protection from a single treatment. However, the costs associated with application, environmental safety concerns about applying insecticides near water resources, and the tremendous reproductive potential of HWA makes this approach less feasible on a broad scale in natural areas. For insecticide guidlines for New York State see Cornell University’s Crop and Pest Management Guidelines http://ipmguidelines.org/. And, consult a certified pesticide applicator.

Laricobius nigrinus adults feeding on HWA
Laricobius nigrinus adults feeding on HWA

To manage HWA at the landscape scale, researchers have been investigating the use of biological control agents. Over the last 10 years, scientists have evaluated the effectiveness of several HWA predators from Japan and the Pacific Northwest including the beetles, Sasajiscymnus tsugae, Scymnus spp., and Laricobius nigrinus as well as fungal pathogens. Some promising evidence has emerged, but further study is needed to test the effectiveness of biological control at larger geographical scales and over the long-term (Cheah et al. 2004).


           

Scymnus sinuanodulus adults, a biological control agent under consideration
Scymnus sinuanodulus adults, a biological control agent under consideration

Homeowners would be wise to take an integrated management approach for HWA-infested hemlock trees on their property. In lieu of systemic insecticides, spraying hemlock foliage with properly labeled horticultural oils and insecticidal soaps may be effective when trees are small enough to be saturated in order to ensure that the insecticide comes in contact with the adelgid. Owners can reduce hemlock tree stress by watering during drought periods and pruning dead and dying limbs and branches. Avoid the use of nitrogen fertilizers on infested hemlocks as it will actually enhance HWA survival and reproduction. Take care moving plants, logs, and mulch from infested to uninfested areas, particularly when HWA eggs and crawlers are present (March – June). Actions such as moving bird feeders away from hemlocks and removing isolated infested trees from a woodlot may also help prevent further infestations.

For more information about hemlock woolly adelgid, visit:

https://henderson.ces.ncsu.edu/hemlockwoollyadelgididentificationandcontrol/
https://blogs.cornell.edu/nyshemlockinitiative/

Woodlot owners should consult Orwig & Kittredge (2005) for available silvicultural options.

Remember, when using a pesticide, first consult your local CCE office or State pesticide guide to identify insecticides that are registered for use in your state and the proper timing for chemical application.

New York Distribution Map

This map shows confirmed observations (green points) submitted to the NYS Invasive Species Database. Absence of data does not necessarily mean absence of the species at that site, but that it has not been reported there. For more information, please visit iMapInvasives.

 

Emerald Ash Borer

EAB on leaf, note irregular edges caused by EAB feeding on leaves. Source: David Cappeart, Michigan State University, Bugwood.org

Hello emerald ash borer. Goodbye ash trees.

The Emerald Ash Borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), commonly referred to as “EAB”, is an invasive wood-boring beetle. Native to Asia, the beetle’s first North American populations were confirmed in the summer of 2002 in southeast Michigan and in Windsor, Ontario. EAB was likely introduced to the area in the mid-1990’s in ash wood used for shipping pallets and packing materials in cargo ships or shipping containers. Emerald ash borers feed on and eventually kill all native ash trees (Fraxinus spp.). Slowing their spread is imperative.

Emerald Ash Borer: Biology and Life Cycle

Learn about the basic biology of EAB.

Emerald Ash Borer: Monitoring and Reporting 

Have you seen ash trees with signs or symptoms of EAB?

Emerald Ash Borer: Management

What are the options for managing EAB?

Emerald Ash Borer: Take Action

Slow the spread and reduce the damage of EAB.

Emerald Ash Borer: Resources

Find external websites, posters, and presentations about EAB.

New York Distribution Map

This map shows confirmed observations (green points) submitted to the NYS Invasive Species Database. Absence of data does not necessarily mean absence of the species at that site, but that it has not been reported there. For more information, please visit iMapInvasives.