Aliens & Pests

The Forestry Commission has announced plans to replace non-native trees in England's forests with native species. The intent is to restore the forests to something resembling the forests of 100 years ago, and to make forests more attractive for wildife and recreation. Up to 20 million trees will be removed over a 20 year period. Reduction of conifer shade should allow native species to reproduce, though enrichment planting will also be funded.  Up to 30% of England's forests consist of ancient woodlands, stands over 400 years old, but which include lots of non-native conifers. The government had encouraged establishment of conifer plantations which today account for 15% of England's forests. Ironically, the government had paid for establishment of the conifer plantations that it is now paying to remove.

A seed is a wonderful place to live if you are a small insect. Protected by the seed coat and the fruit or cone, nourished by storage compounds like starch and fats, a developing insect has everything it needs. Many insects oviposit (plant eggs) directly into developing embryos. If an insect makes the wrong choice and oviposits into an unfertilized ovule, the developing insect may be out of luck. In conifers, unfertilized ovules become empty seeds, and the tree puts no resources into empty seeds.

Patrick von Aderkas of the University of Victoria and his colleagues found that some insects can avoid making the wrong choice by making the plant feed a larva even if the ovule was not fertilized. A tiny chalcid wasp, Megastigmus spermotrophus (Hymenoptera: Torymidae), deposits eggs in Douglas-fir ovules before they are fertilized. As the wasp larva develops, resources are directed to the seed just as if it had been fertilized. Instead of depending on the tree to supply resources to a fertilized see, Megastigmus manipulates seed development to its own advantages.

von Aderkas P et al 2005 Seed parasitism redirects ovule development in Douglas fir. Proc. Royal Society B Early Online Publishing

The US Army Corps of Engineers is planting American elms, Ulmus americana, on a man-made island in the Mississippi River. The Corps planted 21 American elm saplings on Eagle Island to replace other species washed away in a flood. Elms once were a dominant species on Mississippi River bottomlands until they were nearly wiped out by Dutch elm disease. The new saplings come from trees with at least some resistance to the disease. The planting program is part of the US Forest Service American Elm Restoration Project.

Georgia residents are being asked to watch plants in their yard for signs of disease in an attempt to detect infection with Phytophthora ramorum, the fungus the causes sudden oak death. Special attention is being paid to camellias, lilacs, viburnum, azaleas, rhododendron and mountain-laurel. These plants are known hosts for the fungus, which usually causes leaf spots or twig dieback. The fungus can be fatal to oak trees, and the program is an attempt to eliminate the disease from home gardens before Georgia's valuable and extensive oak forest is infected. Ornamental plants were sent to Georgia from infected Monrovia nurseries in California, so state agriculture authorities suspect that infected plants are in the state. Georgia authorities quarantined plants shipped from Monrovi and other California nurseries, but not until over 49,000 plants had been sold.

Scouts in Washington D.C., equipped with handheld computers, are surveying 8.500 American elms, Ulmus americana, on streets and city property. The scouts are looking for symptoms of Dutch elm disease. Trees with symptoms are reported to urban foresters, who then examine the trees further and prescribe treatment if necessary. The city, which once had over 25,000 American elms, has not surveyed trees in several years. With the infusion of funds from Casey Trees, scouting is now possible. American elms can be conserved through a combination of treatment and sanitation, but scouting is the first requirement. The National Park Service has a comprehensive program to preserve elms on Federal property

National Public Radio has a story by Margot Adler about smoke jumpers climbing trees in and around Central Park looking for Asian longhorned beetle. The story includes vivid descriptions of tree climbing. Previous story: Smoke Jumpers in Central Park

Adult Asian longhorned beetle, Anoplophora glabripennis. Photo courtesy APHIS, US Department of Agriculture

      

In the two years since the "EAB" was first found in Ohio, over 200,000 trees have been cut down in an effort to confine the infestation. As we have reported previously, new outbreak areas have been found this year. Ash removal has been paid for by funds from the US Department of Agriculture. As the borer infestation spread, costs may be shifted to land owners. At least 10% of all trees in Ohio are ash trees (of several species). The Ohio state forestry division estimates that if the infestation spreads throughout the state, direct costs for removal could top $1 billion. This does not include the cost of the lost of ash trees in forests, including the timber value and the loss of ecosystem services. Nor does it include the cost of street tree removal by cities or the cost of increased heat loading of city buildings with the loss of shade trees. In Ann Arbor, Michigan, residents will probably vote in November on a referendum to allocate $4 million for ash removal in the city. This does not include the cost of tree replacement. Timely removal is critical for controlling the spread of "EAB" but also to remove hazardous trees. Ash trees attacked by "EAB" die quickly and become hazardous, with falling dead limbs and entire trees prone to falling. Some smaller towns are trying to head off the borer by using state and federal funds to replace ash trees before the borer arrives. Bowling Green, Holland, Rossford, Sylvania and Rossville Ohio are removing ash trees and replacing them with species that are not susceptible to "EAB". "EAB" information can be found at http://www.emeraldashborer.info.

Adult emerald ash borer, Agrilus planipennis. Photo by James Zablotny, US Department of Agriculture

      

Roving bug-detection patrols will be scouting southwestern Ontario this summer looking for evidence of "EAB". The inspection areas are mostly outside Essex County and Chatham-Kent, where thousands of trees have been cut to stop the spread of the Asian insect, which is lethal to ash trees. Inspectors will be visiting sawmills, private campgrounds and provincial parks looking for ash firewood that might have been brought in from infested trees. Last year, 22 fines of C$400 were imposed on people who illegally moved firewood out of the quarantined areas. Movement of wood by people is a much greater threat than natural movement of the beetle, since firewood can be hauled over long distance in a short time. Adult beetles have begun emerging in Ontario, and will be colonizing new trees However, the extent of new damage will not be known until fall or spring, after larvae have fed on the tree stems and girdled the trees. In Ohio, tree climbers have inspected trees in Maumee Bay State Park and found beetle larvae in seven trees. The trees have been removed. Ash trees within 200 yards of the infested trees were girdled to create 'trap trees.' Stressed trees are more attractive to ash borers than unstressed trees. Girdled trees are more attractive to adult beetles than ungirdled trees and trap trees may attract all the emerging adults, preventing them from flying further afield and spreading the infestation. Trap trees will be removed next spring before adult beetles emerge. The effectiveness of this strategy is not known. It is probably less effective than removing all ash trees in the area, but removal budgets are tight.

Adult emerald ash borer, Agrilus planipennis. Photo by James Zablotny, US Department of Agriculture

The latest Tangled Bank is up at Geomblog. Tangled Bank is a blog carnival for science writers. The current offering has lots of great articles and is worth a visit.

     

There are continuing conflicts between property owners and state authorities trying to enforce ash tree removal to prevent spread of "EAB". We have previously reported several stories on these conflicts. In Port Huron, MI, property owners are trying to stave off the ash removal program by treating the trees with systemic pesticides known to deter the beetle. However, the treatments are expensive and need to be repeated annually with no end in site. State authorities have not agreed to permit treated trees to remain. Since the state has no guarantee that the property owner will continue treatment, or that the treatment is 100% effective, authorities are unlikely to permit the trees to stand. The "EAB" control program requires removal of healthy ash trees within 200 ft. of infested trees (farther in some states). Property owners often do not recognize the need to remove apparently healthy trees. It is a difficult task for agricultural authorities to sell property owners on the need to remove trees, especially prized shade trees, when there is nothing wrong with them. This is a public relations problem for the states trying to prevent spread of the "EAB".

Adult emerald ash borer, Agrilus planipennis. Photo by James Zablotny, US Department of Agriculture

     

The "EAB" has spread in northern Ohio, and is now in downtown Toledo and Maumee Bay State Park. State officials are planning aggressive ash tree removal programs for both areas. The Maumee Bay infestation is particularly worrisome: "The most disconcerting news for state officials was the discovery of infested trees at Maumee Bay State Park in eastern Lucas County. That means the beetle has moved perilously close to the Lake Erie shoreline and could spread eastward across northern Ohio - something officials have been fighting to avoid. They fear the pest will be much harder to stop if it enters wetland areas in state preserves and the Ottawa National Wildlife Refuge in Ottawa County that have limited road access. "I can confirm it has been infested," Lee Anne Mizer, agriculture department spokesman, said yesterday of Maumee Bay State Park. She refused to elaborate, indicating the state plans to discuss details on Monday." - Toledo Blade

Adult emerald ash borer, Agrilus planipennis. Photo by James Zablotny, US Department of Agriculture

The winter moth, Opheroptera brumata, was introduced into North America from Europe. Caterpillars of the winter moth are summer defoliators of maples, apples and blueberries.  Long a problem in southern Canada, the winter moth has established itself in Massachusetts and Rhode Island. Winter moth adults emerge in November and December, and many communities in Massachusetts had dense flights of the moths last fall. These areas are now seeing extensive defoliation.

Defoliated trees are weakened somewhat, but spring defoliations are generally followed by a flush of new growth and recovery. Several years of consecutive defoliation can reduce tree vigor, especially if other stressors such as drought also reduce vigor. Defoliation can severely depress fruit production. The winter moth is unlikely to become as serious a problem as the gypsy moth, and effective biological control agents are already known. In Canada, winter moths have been controlled by the introduction of a predatory wasp, Cyzenis albicans, and Massachusetts authorities are raising trial populations of the wasp. It could take several years before wasp populations are high enough to control the winter moth.

The last few years have seen major increases in defoliation from multiple causes in New England. Defoliation by native insects is at all-time high levels. Insect outbreaks are often regulated by weather. Mild winters, such as we have had in recent years, permit higher insect populations to survive. Global warming is thus a likely cause of increased insect infestations.

A hemlock tree, planted in a yard 14 years ago, died suddenly. The homeowner left town with the tree apparently healthy and returned two weeks later to find the tree had lost all its needles. On inspection, all the above-ground parts of the tree were dead. We excavated the tree with an Air Knife to see if there were below-ground signs or symptoms that might indicate the cause of death. We found extensive injury to the cambium, phloem and xylem below the ground level of the tree.
 

Stem of a dead hemlock showing extensive injury.

What caused all this damage? Read more for the solution.