The goldspotted oak borer, Agrilus coxalis Waterhouse (Coleoptera:Buprestidae), is adding to the woes of California’s magnificent oak forests. 

While sudden oak death is killing oak and other trees in the northern part of the state, the oak forests of the southern part of the state have escaped damage due to the dry conditions that prevent spread of the disease. 

Now, the goldspotted oak borer is causing oak mortality in the southern part of the state.  Like other Agrilus beetles, such as the emerald ash borer and twolined chestnut borer, the goldspotted oak borer kills trees when the larvae feed on the phloem and cambium.

The borer, first identified during oak mortality surveys in 2004 in San Diego County, has been found attacking coast live oak, Quercus agrifolia, canyon live oak, Q. chrysolepis, and California black oak, Q. kelloggii, on the Cleveland National Forest.  It is now considered a major cause of oak mortality in Southern California.

The goldspotted oak borer is native to parts of southern Arizona, Mexico and Guatemala. It has not previously been considered a major pest in those areas.  While the borer may have extended its range naturally, is it likely that it was introduced into southern California by movement of firewood, as with the emerald ash borer.

It remains to be seen how significant a pest this will turn out to be.  Major mortality was not seen until 2008 in Cleveland National Forest, and it will take some years to assess the extent of the outbreak.  A risk assessment by the US Forest Service (click map for details) shows that oak forests throughout California are at risk from this pest.

Additional information:  USDA Forest Service Pest Alert: Goldspotted Oak Borer. (pdf, will open in new window)

The New York Times has an outstanding video, “America’s Disappearing Forests”  documenting the devastating impact of the mountain pine beetle (Dendroctonus ponderosae) on lodgepole pine (Pinus contorta) in the Rocky Mountain states.  The insect has destroyed about 2 million acres of lodgepole pine forests. Since lodgepole pine typically occurs in pure stands (coming in after fire), the insects are in effect wiping out entire forests.

It is becoming clearer that the main cause of the outbreak is the prolonged drought of more than 8 years, and mild winters.  The prolonged drought weakens the ability of the trees to fight off beetle attacks. The mild winters allow higher survival rates in the beetles.  Since the western states will only become warmer and growing seasons longer, there is no end in sight to the outbreak except the death of lodgepole pines.  This does not mean the end of forests in the region, since other species can occupy the space. However, the loss of a dominant species in an arid environment means that it will take a long time, centuries at least, for the forests to recover.

Picture: lodgepole pine mortality due to mountain pine beetle. Photo courtesy of Jerald E. Dewey, USDA Forest Service, bugwood.org.

America’s Disappearing Forests – The New York Times – Video Library

The Big Five: emerald ash borer, Asian longhorned beetle, Sirex wood wasp, sudden oak death, hemlock woolly adelgid

Forests in eastern North America are beset with a number of exotic pests and pathogens. Several of these pests and pathogens collectively could have a larger impact on eastern forests than chestnut blight, which killed billions of trees in the first half of the 20th century.  This article is a brief introduction to the Big Five.  Expanded articles will follow over the next month.

There are 4 insects and 1 disease that, in my opinion, represent the biggest threat to eastern forests.  Although there are other major pests and pathogens, both native and exotic, these five either threaten a large number of important tree species or threaten a single very important tree species.  ‘Important’ refers to commercial value of the species, ecological importance or both.

The Big Five (each link is to a longer article which will be updated frequently. NOTE: The linked articles will be available on November 27):

1. Sudden Oak Death (SOD). Caused by the fungus Phytophthora ramorum. A major disease in California, SOD threatens the dominant oak forests of the eastern US.  Transmission is mainly through shipment of stock from infected nurseries in the west. A vigorous inspection and sanitation program in nurseries is slowing the spread of the disease. 
2. Emerald ash borer (EAB). The emerald ash borer is a small, brilliant green beetle native to Asia. It was first found in North America feeding on ash trees in southeastern Michigan in 2002, and is now in 10 US states and Ontario. The beetle kills all ash (Fraxinus spp.), but white, green and black ash are particularly susceptible.
3. Asian longhorned beetle (ALB). The Asian longhorned beetle first appeared in Brooklyn NY in 1996, probably hitching a ride on pallets and other wood containers from China. ALB outbreaks are primarily urban. If the insect spreads into eastern forests, many tree species are threatened. Hosts include maples, buckeyes, willows, elm, birch and sycamore, though other species may be susceptible if ALB reaches high populations.
4. Hemlock woolly adelgid (HWA). The hemlock woolly adelgid, a sucking insect native to Asia, has been in the US sine 1924, slowly spreading to encompass much of the range of eastern hemlock. Although it is spreading slowly, it has the potential to wipe out eastern and Carolina hemlocks throughout their native range.
5. Sirex wood wasp.  The Sirex wood wasp is a major pest of pine trees throughout Europe and Asia. The female wasp lays eggs in pine bark and injects both a toxic mucus and a fungus. The toxin kills tree cells, the fungus grows on the dead cells and the wasp larvae feed on the fungus. Further outbreaks of the wasp are expected, as it hitches rides in wood packing materials. Sirex wood wasps have been found in 15 New York counties, several areas in Ontario, and in Pennsylvania and Vermont. The greatest economic threat is to the southern pine industry, but Sirex wood wasps have not yet been found outside of the northeastern US.

Each of these pests and pathogens poses a threat to particular tree species. Collectively, they threaten the entire eastern forest region.  Emerald ash borer is completely beyond the ability of sanitation and quarantine protocols to control its spread, and it is only a matter of time before the beetle is found throughout the range of ash trees.  Hemlock woolly adelgid is also beyond our capacity to control.  Whether sudden oak death, Asian longhorned beetles and the Sirex wood wasp will reach epidemic proportions is impossible to predict. Vigorous surveillance is so far holding SOD at bay in the east, while Asian longhorned beetles are gaining ground in Massachusetts.

The impact of these pests and pathogens on our forests is closely tied to the impacts of global warming. As the earth warms, habitat conditions for tree species will shift northward. The ability of trees to shift ranges in response to global warming depends on the existence of suitable habitat. The Big Five, as well as other insect and disease problems, may fundamentally alter the structure and function of eastern forests well before the major impacts of global warming occur, and may limit the ability of trees to migrate in response to a warming climate. For example, if warmer conditions allow the hemlock woolly adelgid to become well established at the northern limit of the current range of eastern hemlock, there may be no northward migration of hemlock because trees on the northern fringe will be killed.

Please check back for frequent updates on these pests and pathogens. Although there are many web sites describing each of these individually, there does not seem to be an effort to track information collectively about all these problems.  If any reader knows of such an effort, please post a comment.

Picture credits (all images used by permission):

• emerald ash borer, David Cappaert, Michigan State University, Bugwood.org
• Asian longhorned beetle, Pennsylvania Department of Conservation and Natural Resources – Forestry Archive, , Bugwood.org
• Sirex wood wasp, David R. Lance, USDA APHIS PPQ, Bugwood.org
• sudden oak death (canker on tanoak), Joseph O’Brien, USDA Forest Service, Bugwood.org
• hemlock woolly adelgid on eastern hemlock, North Carolina, picture by Tom Kimmerer.

Trees are host to a bewildering array of fungi. Fungi that live inside the tree’s body (rather than on the surface) are known as endophytes. Endophytic fungi produce a lot of interesting chemical compounds, including antibiotics and hydrocarbons.

Gary Strobel and his research group at Montana State University have found a fungal endophyte in a Peruvian tree that produces a complex array of hydrocarbons that resemble diesel fuel.  They are calling this mix of products mycodiesel.

The fungus, Gliocladium roseum, can produce mycodiesel using cellulose as a substrate in culture. This suggests that the fungus is a wood decay organism, though its biological role as an endophyte is not known (some endophytes cause disease, some protect trees from disease, some have no known role).  The fungus was found on the Peruvian tree ulmo (Eucryphia cordifolia)

The big question that many people will ask is whether the fungus can be made to produce enough diesel-like fuel to make it economically important.  While the popular press is trumpeting mycodiesel as the fuel of the future, it is way too early to know whether the discovery is of any commercial significance. Making the transition from laboratory yields to industrial yields is a long and expensive process.

But there is no question that this is a discovery of substantial biological importance. Teasing apart the mechanisms that allow this fungus to produce so many hydrocarbons will illuminate the biochemistry of hydrocarbon biosynthesis in fungi. 

The discovery is also a testament to the career-long commitment of Professor Strobel to research on endophytic fungi. His lab has produced a consistent stream of important research results based on his passion for these fungi, which have largely been ignored by other biologists.

Picture: Gliocladium roseum, an endophytic fungus from the Peruvian tree Ulmo. Photo from Gary Strobel’s lab.

Sources:

• The production of myco-diesel hydrocarbons and their derivatives by the endophytic fungus Gliocladium roseum (NRRL 50072) — Strobel et al. 154 (11): 3319 – Microbiology.
• Full article as a .pdf from Gary Strobel’s web site
• MSU-led team finds new type of fuel in Patagonia fungus – MSU Press Release
• Scientists discover tree fungus that could provide green fuel for transport – The Guardian
• Endophytes, from Fungal Biology, University of Sydney, Australia

Gardeners at a historic estate in Derbyshire, England, have discovered the disease sudden oak death on rhododendrons, and fear that it could spread to ancient trees on the estate. Sudden oak death has been found at over 500 sites in England. English oak (Quercus robur) does not appear to be harmed by the disease. However, many other trees common in England are susceptible, including beech and conifers. The disease has been found mostly in rhododendrons, azaleas, viburnums and camellias in England. In 2004, a significant outbreak of the disease was found in Wales on holm oak, Quercus ilex.  In the US, thousands of trees have been killed by sudden oak death, caused by the fungus Phytophthora ramorum, prompting an aggressive response to the disease by British authorities.

Sources:

• BBC NEWS – Disease threatens ancient trees
• BBC News – Sudden oak death 
• Sudden oak death – California oak mortality task force

The first emerald ash borer (EAB) in a tree coming from a nursery has been found in Kenosha County in southern Wisconsin. The ash tree, from a nursery in Lake County Illinois, was planted near Silver Lake, WI.  Emerald ash borer infests and kills all North American ash trees (Fraxinus).

Interstate transport of nursery trees from states with known emerald ash borer infestations is a violation of the federal EAB quarantine.

The emerald ash borer has destroyed millions of ash trees in Michigan, Indiana, Ohio, Pennsylvania, Maryland, Illinois, West Virginia, Virginia, Missouri and the Canadian provinces of Quebec and Ontario.  Wisconsin has been trying to prevent the movement of firewood and nursery stock from Illinois.  Given the large number of vacationers travelling from Illinois to Wisconsin, importation of the beetle in firewood seems only a matter of time.

Picture: Emerald ash borer adult, Agrilus planipennis Fairmaire, courtesy of David Cappaert, Michigan State University, bugwood.org

news: Emerald ash borer found in tree from nursery