By Michelle Ma
About 450 nonnative, plant-eating insect species live in North American forests. Most of these critters are harmless, but a handful wreak havoc on their new environment, attacking trees and each year causing more than $70 billion in damage.
The problem is, scientists often don’t know which insect will emerge as the next harmful invader.
A team led by the University of Washington, drawing largely on the evolutionary history of insect-plant interactions, has developed a way to understand how nonnative insects might behave in their new environments. The team’s model, described in a paper appearing Oct. 17 in the journal Ecology and Evolution, could help foresters predict which insect invasions will be problematic, and help managers decide where to allocate resources to avoid widespread tree death.
“What makes the bad invaders so special? That has been the million-dollar question, for decades,” said Patrick Tobin, an associate professor in the UW School of Environmental and Forest Sciences and one of the project leaders. “This has the potential to profoundly change how we predict the impact of nonnative species and prioritize limited resources used to mitigate these impacts.”
The new model can quickly evaluate whether a newcomer insect, even before it gets here, has a high probability of killing a population of North American trees. To use the model, all that’s needed is information about the insect’s feeding method (wood, sap or leaf feeder, for example) and what trees it feeds on in its native range. The model will then determine whether any North American trees are at risk of dying from it.
Whether a nonnative insect takes hold and becomes destructive has more to do with the evolutionary history between the new (North American) host tree and the insect’s native host tree from its home region, Mech explained. Molecular tools that allow scientists to construct comprehensive phylogenies (or maps) of how tree species evolved was key to the team’s breakthrough.
For example, if a pine tree in Asia and another in North America diverged tens of millions of years ago, the North American pine likely wouldn’t have retained defenses against an insect that only lives with the pine in Asia. Alternatively, two pines on both continents that share more evolutionary history and diverged more recently might still share similar defenses.
The new model helps identify the evolutionary “perfect storm” for conifers, where the invasive insect still recognizes the new tree as a food source, but the tree hasn’t retained adequate defenses to keep the invader in check.
Jeff Mulhollem, Pennsylvania State University
Genes in green ash trees that may confer some resistance to attacks by the emerald ash borer express themselves only once the tree detects the invasive beetle’s feeding, according to Penn State researchers.
Knowing this, geneticists may be able to selectively breed trees to strengthen them and perhaps move the resistance response earlier to ward off the beetles’ onslaught, explained John Carlson, professor of molecular genetics.
Green ash, an ecologically and economically valuable tree species native to eastern and central North America, is under severe threat from the rapid invasion of emerald ash borer, a wood-boring beetle native to Asia. Penn State scientists and others are trying to save the species.
Prior observations in a green ash provenance trial—an experiment to see how plants adapt—planted at Penn State in 1978 by Kim Steiner, professor of forest biology and director of The Arboretum at Penn State, and colleagues in the U.S. Forest Service, show that a very small percentage of ash trees survive emerald ash borer infestations, seemingly because their tissues do not nourish and perhaps even sicken the beetles.
“Emerald ash borer probably entered the provenance trial unnoticed around 2008 and trees started showing symptoms of attack by 2012,” Carlson said. “All but eight or nine of the approximately 1,800 trees that Kim planted have subsequently been killed by the beetles.”
Ash trees succumb after adult beetles lay eggs on their bark. When the eggs hatch, the larvae bore into the bark and feed on the transportation tissues of the tree. This disrupts the movement of nutrients and water within the tree, girdling it and causing death.
“To better understand the response of green ash trees to emerald ash borer, we compared gene expression data for resistant versus susceptible green ash genotypes exposed to attack by the beetles,” said Carlson, director of Penn State’s Schatz Center for Tree Molecular Genetics. “By comparing RNA-sequence data from stems attacked by emerald ash borer to multiple tree tissues under other stresses, we could identify differences in the gene expression profiles specific to emerald ash borer resistance.”
BY ROBERT LANGELLIER
The chinquapin was supposed to have been wiped out by blight. Now one determined Missouri naturalist is hand-pollinating trees in secret groves to bring it back.
STEVE BOST WILL show you some Ozark chinquapin trees. “But I’d have to blindfold you before you get in the car,” he jokes.
Deep in the rolling southeast Missouri Ozarks, Bost gets out of his car at the end of a remote dirt road. Somewhere nearby, carefully hidden from the public, is the Ozark chinquapin tree, once a keystone Ozark forest species. Decimated by chestnut blight in the mid-1900s, any viable trees were thought to be long gone—that is, until Bost found a few healthy hangers-on in the 2000s. Now he’s trying to bring the tree back from the edge of blight in a non-traditional way. And he’s succeeding.
By Sandra E. Garcia
They hope to fight the thriving black markets for illegally logged timber.
Forests are disappearing. Maps show shrinking woodlands all over the world. Even trees coveted for their wood that are protected from logging are chopped down.
Worried about such deforestation, environmental advocates are driving a project to create a DNA database of populations of the bigleaf maple tree on the West Coast. The eventual goal is to use DNA mapping to combat the thriving black markets for timber in tropical countries that are plagued by illegal logging.
“We are taking leaf tissue from the maple trees and taking samples along the entire length of the species range from Southern California to British Columbia,” said Meaghan Parker-Forney, a science officer with the World Resources Institute, a nonprofit group that promotes environmental sustainability and is working on the monthslong initiative.
The DNA database is an experimental project for the Norwegian government, which is jointly funding the effort with the United States Forest Service’s international program. Norway hopes to see whether such a database is feasible in places like Indonesia and Peru, where illegal logging is rampant.