Ash trees make up six percent of the tree population in Connecticut, and they are under threat of decimation. Dr. Sourav Chakraborty, Assistant Professor of Chemistry at Central Connecticut State University (CCSU), has been investigating the ash trees as they were attacked by the Emerald Ash Borer (EAB) beetle across the state. The research conducted by Dr. Chakraborty and his students will help us understand the survival strategies of the trees against the EAB and educate residents on how to mitigate the outbreak of similar invasive species.
“EAB is an invasive insect pest which was accidentally imported from Asia and landed in the Detroit area in the late 80s or early 90s,” says Dr. Chakraborty. He added, “The state entomologists investigated the problem and identified D-shaped exit holes in the bark of the ash trees in 2002. The beetle was identified but by that time, thousands of larvae were already feeding on the trees.”
The EAB is methodical and relentless. “The female lays eggs on the bark, then the larva chew through the outer bark and reach the inner bark. The inner bark––which is known as the phloem tissue––is soft and contains a lot of food, including sugar,” says Dr. Chakraborty. “That soft tissue lets sugar travel from the leaves to the roots. The voracious larva feed on the tissue and cut the nutrient transport causing a ‘girdling’ effect, starving the roots and stressing the tree. Eventually, this causes the tree to die.”
“Invasive species are something that people hear very little about,” explains Dr. Chakraborty. “But when students start the research they become intrigued and look more closely at the overall impact. We want to educate kids so they can develop problem-solving abilities and keep their eyes open in the field.”
Dr. Chakraborty and his students have a difficult task ahead of them. EAB was first detected in Connecticut in 2012 and it has been active ever since. “It was first discovered in New Haven County and is constantly spreading,” says Dr. Chakraborty. “The only parts of the state still untouched are the northwest and southeast. This doesn’t mean they’re not there, we just haven’t found them yet.”
Dr. Chakraborty recently started a collaboration with Dr. Arango-Velez of the Connecticut Agricultural Experimentation Station (CAES). As Dr. Chakraborty explains, “I was speaking with one of my colleagues at University of Alberta about pine trees and pine beetles, and he mentioned that Dr. Arango-Velez was at CAES working on EAB, so I reached out. She was excited because she had carried out some work on tree physiology and anatomy, but not really on tree chemistry.” Their collaboration helped them see that the EAB problem extends beyond what Dr. Chakraborty originally observed. According to Dr. Chakraborty, “We are finding the insect is adapting and starting to attack other tree species such as white fringe trees. This is unusual for EAB because it is a specialized insect that feeds only on ash trees.”
While CAES has a wide focus, Dr. Chakraborty’s work with Dr. Arango-Velez focuses on tree metabolites. According to Dr. Chakraborty, “Dr. Arango-Velez is a tree physiologist working on the effect of drought on tree health and how invasive species attacks the trees under such conditions. There are ash trees in Asia–where the beetle is from––and the beetle population is controlled there. So there’s something—possibly a coevolutionary history––with the Asian ash trees that allows them to survive.”
There are concerns that if EAB can move from the ash to white fringe trees, it could potentially adapt to attack other, more commercially-significant tree species. Currently, there are multiple “bio-surveillance” activities, such as parasitoid release, being employed to control the progress of the EAB. “There are wasps from Asia that attack EAB larvae and the hope is that they will kill the larvae and the eggs in the field,” says Dr. Chakraborty.
However, Dr. Chakraborty is cautiously optimistic and suspects that the wasps will not serve as magic bullets. “Sometimes the imported species become invasive in the new environment,” warns Dr. Chakraborty. “There are also woodpeckers that feed on the EAB larvae, and while their activity was shown to be increased in EAB infested areas, this is a major invasion of the EAB, proving these methods have limitations. The bottom line: EAB is constantly being discovered in new counties and states which informs us that the existing methodologies failed to completely stop the progress of this beetle.”
Dr. Chakraborty, along with his colleagues at Ohio State University, identified a few metabolites and proteins which are different between the Asian ash trees and North American ash trees. These proteins and metabolites might hold the key to the resistance traits of Asian ash trees against the EAB. He explains, “This will help us develop a tree breeding approach with resistance in the trees.”
The average Connecticut citizen does have a role to play in the fight against EAB. “Do not move firewood!” pleads Dr. Chakraborty. Infested firewood, when moved to another location, can introduce the EAB to healthy forests. He further explains, “If logs are stored, EAB can go into hibernation and come back out in the summer. All we need is some consciousness. If we’re conscious, there’s a good chance to reduce the impact.”
The EAB forces one to consider the prospect of altered forest dynamics, but it is too soon to predict the full effects of this scourge. “Only time will tell what will happen,” says Dr. Chakraborty. What’s certain is that the obliteration of the ash tree will have a significant impact on the state, altering its landscape and geography, and impacting shade and property values. Probably another tree species will grow and take over until the next generation of insects hit them. The dynamics will definitely shift and a new equilibrium will be reached over time. The USDA Forest Service Northern Research Station in Delaware, Ohio is building an ash seed bank for future regeneration, if worst comes to worst.”