The Biology Department invited Post-Doctoral Research Specialist Sara Tanis from Michigan State University to give a talk entitled “What’s Under the Bark? A look at native and exotic insects in hardwood forests” on Monday, March 21. The lecture discussed the danger posed by exotic insects targeting – and killing – millions of healthy trees in the United States. 

These invaders are not only reaching deep into the pockets of American homeowners and the U.S. government, but are also decimating forest landscapes. So what exactly is the problem, and how can we put a stop to this destruction?

Tanis opened the lecture by underscoring the importance of forests and trees to both natural and urban ecosystems. In addition to providing food and habitat, preventing soil erosion and increasing property values, trees also cool down cities. Tanis turned to Colgate’s landscape to further articulate this point.

“You have beautiful trees on this campus. And I bet you seek out the shade of those trees when it’s hot,” Tanis said. 

After demonstrating that the value of trees cannot be overstated, Tanis turned to the subcortical insects, or the small bugs residing in the nutrient rich areas right under the bark, that are native and non-threatening to American forests. Tanis explained that native woodborers and trees have maintained a balanced ecosystem through the process of co-evolution. 

“Trees get stronger, then the insects get stronger. But trees defend themselves, and this is something that not a lot of people understand. […] Native insects only attack dying trees because the healthy ones are strong enough to defend themselves,” Tanis said.

So if woodboring pests are only attacking dying trees, what’s the problem?

“The problem comes in when we start talking about exotic forest insects,” Tanis said.  

Over 455 species have been introduced to the U.S., and as global trade continues to increase, opportunities for these insects to arrive, survive and thrive also increase. And once these invaders have established a population, huge losses in biodiversity and ecosystem services promptly follow. Because these exotic forest insects do not share an evolutionary history with their host trees, they can power through forest defense systems and take down both healthy and dying trees. 

Exotic insects are also a financial threat – costing the U.S. about four billion dollars annually. Each time a single tree needs to be taken down, homeowners and/or the government pay thousands of dollars.

“So yes, these insects can cause a lot of damage,” Tanis said. 

Tanis introduced the Emerald Ash Borer (EAB) to demonstrate the magnitude of damage these bark dwellers can produce. Although EAB only colonizes stressed trees in Asia, the exotic pest takes down both dying and healthy trees in North America. 

“It’s a beautiful green beetle, but the most destructive pest in North America. It even has its own comic book,” Tanis said. 

Once an EAB targets its selected prey – the ash tree – it is only a matter of two years before the tree is dead. Already costing the U.S. over ten billion dollars just in tree removal, EAB has decimated ash tree populations in thirty states, with independent infestations proving to be a dangerous consequence of people moving firewood. 

“I’m gonna ask you please, please, don’t ever move firewood,” Tanis said. 

The Asian Longhorned Beetle (ALB) is another exotic Asian woodborer that is currently obliterating our innocent trees. As a generalist, ALB targets a wide range of hosts, thereby potentially posing an even greater threat than the EAB. Although currently contained to urban areas, many are terrified that ALB will sneak into our natural landscapes. 

“If this gets out, we are looking at around $650 billion dollars,” Tanis said. 

Eradication of infested trees due to ALB infestation is also very emotionally taxing for homeowners. 

“How many of you had a tree as a kid? [Hands fly up] With this particular pest, you have no control whether that tree gets cut,” Tanis said. 

Tanis reassured the audience by discussing what she and her colleagues are doing to ensure that our childhood trees avoid the cut.  

“We develop these things called risk maps. They show me hot spots of where I need to go to set traps to catch these guys,” Tanis said. 

The traps are placed atop the canopy and scented with a variety of chemicals mimicking natural pheromones and host volatiles in order to lure the pests

into captivity. 

“We’ve caught a lot of bugs […] Mostly bark beetles and longhorn beetles […] And we’ve learned a lot about our native fauna,” Tanis said. 

Understanding the importance of early detection and rapid response, Tanis and her research team have made large strides in exotic pest control, but significantly more work needs to be done to cut down costs and stop cutting down trees. 

Senior Jillian Belgrad attended the lecture and was shocked by the scale of damage revealed by Tanis. 

“I hadn’t realized how widespread of an issue bark-targeting exotic species are,” Belgrad said. “This lecturer really opened my eyes to both the severity and prevalence of these problems. I’ll definitely look at trees around us much differently now.”