My hands are a bit sore. So are my shoulders. I spent the last two evenings with an ax in my hand. I really wish that wasn't the case. I tried hard to keep the two ash trees that I hacked up alive. Their deaths, while not caused by chemistry, were due to a failing of chemistry.
I live in Michigan, a state now past the crest of an infestation of the emerald ash borer. The infestation is on the wane because there are so few ash trees left. The borer has killed them all. It is an ugly death. The borer is a tiny bug, less than half an inch long. The borer eats ash leaves, a minor issue for the tree, but when it mates, eggs are deposited on the bark of the tree. Larvae emerge and burrow into the bark. It is the larvae that ultimately kill the tree.
The larvae tunnel. They tunnel into the bark into the cambial layer, the region between the outer bark and the wood, where they will spend their larval phase. They feed on phloem, the layer that conducts sugar and other nutrients to the tree. The action of the larvae distrusts the flow, depriving the tree of nutrients, slowly killing the tree. The pupae hunker down for the winter, erupting through the bark in the spring. Infected trees begin to lose their outer bark, resulting in “blinding” patches where the smooth, orangish underbark is exposed by the loss of the rough, gray, weathered outer bark.
I am not clear on whether it is the emergence of the beetles or the action of predators hunting the larvae that knock the bark off the tree. What I am clear about is how depressing it is to look at a majestic tree with its bark falling off. Whole forests of ash trees stand in Michigan, dead, with their rough bark removed, now dot the landscape.
Two of the largest trees on my lot were ash trees. One was by far the tallest tree around. It was a magnificent tree, over eight feet in circumference at its base. About 30 feet off the ground, it split in a beautiful Y, each arm reaching skyward, ultimately reaching about 70 feet. It was a tree that I assumed I could save from the scourge sweeping through Michigan.
The borer is native to Asia, assumed to have arrived in the Detroit area in the 1990s. First reports of dead trees in Detroit were in 2002. My ash trees are a two hour drive away from those first dead trees. I first saw an ash borer about 6 years ago. I remember it well. It is a striking bug, a beautiful iridescent emerald green. It had taken about 8 years to go 120 miles. Signs in southern Michigan were warning about the borer, mandating steps to keep it from spreading and requesting reporting of any infestation. By the time that I called to report my sighting, it was old news for my area. Today, reporting for Michigan’s Lower Peninsula is no longer required: the area is fully infested.
I decided to save my ash trees through chemistry. Imidacloprid is a systemic insecticide, a member of the frequently maligned neonicotinoid family. I spent a total of several hundred dollars in my attempt to save the trees. They both leafed out last year, at least two years after every other ash tree in the area was dead. By the end of the summer, large areas of the crowns of both trees had lost their leaves. Areas of the smooth orange bark could be seen with binoculars. The patient was clearly dying. Chemistry had let me down.
The trees are now down, cut down during the winter. Counting tree rings on a big tree is harder than I thought it would be. The big tree was more than 60 years old. I am not sure that I can accurately say it was struck down in its prime, but it was surely earlier than it should have been. It was one of the only times in my life that a pest problem wasn't solved quickly and easily with chemistry. This time biology won.
We are on a precipice with the arrival of powerful synthetic biology tools, if we haven’t already tumbled over. Biologists – or are they biochemists? – have now engineered and released mosquitos modified to destroy a population. In this case, it is the Aedes Aegypti mosquito, an invasive species to the Western Hemisphere, but one that has been here for centuries. I don’t have great love for any animal intent on sucking blood, but A. Aegypti is a disease carrier. It is commonly called the Yellow Fever Mosquito, but more lately it has been implicated in carrying a host of other diseases including chikungunya, dengue fever and, most recently, zika.
Oxitec has completed a number of successful trials releasing “self-limiting” mosquitos. That is the name given to their genetic modification that creates mosquitos that require tetracycline to reproduce normally. Without it, the offspring die.
Releasing mosquitos carrying the trait can cause a rapid drop in the population, potentially eradicating it. I didn’t realize that we had gone so far as to release such organisms into the wild. I thought it was still a matter of discussion, as it is in the CRISPR/Cas9 discussion. Gene drives made possible with this powerful new technology hold the promise of creating traits that are always inherited, including those powerful enough to wipe out a species.
Society cannot bring itself to destroy the last samples of smallpox, scourge that it is. Yet, we’ve taken steps to eradicate a higher species. I feel a bit uneasy about the potential to destroy a species that is in an established, larger ecosystem, even one as easily hated as a disease carrying, blood sucking pest. It is clear that the technology is ready to go. The ACS will hold a series of talks examining the power and implications of genetic modifications at the Philadelphia National Meeting. I am hoping that it brings some clarity to my thoughts on the matter.
As I look at the pile of ash firewood that was once a magnificent tree, I feel sad that gene drives or self-limiting modified ash borers were not deployed to stop the invasive borer. I would have deployed them to stop the emerald ash borer. It is rapidly moving and invasive. It does not belong in the ecosystem here and it is well isolated from the native population. It is too late for my ash trees, but not too late to stop the scourge before it wipes out every ash tree. It is also not too late for the next time an invasive scourge begins to wreak havoc. I don’t know when it will happen, but history teaches us that it certainly will.
Mark Jones is Executive External Strategy and Communications Fellow at Dow Chemical since September 2011. He spent most of his career developing catalytic processes after joining Dow in 1990. He received his Ph.D. in Physical Chemistry at the University of Colorado-Boulder doing research unlikely to lead to an industrial career and totally unrelated to his current responsibilities.