Authors notes:

Trees die within 2-3 years after initial attack.

Ash is a hardwood tree – commonly used for canoe paddles and the handles of a lot of hand tools like hammers, or shovels. “A lot of industries are quite worried about the potential loss of ash trees,” says Haack. “Ash right now is a very common tree that’s planted, there’s more than 20 species of ash in the United States, and it basically occurs in every single state of the continental U.S. And it’s commonly planted along streets because it’s somewhat tolerant to a lot abuse and pollution and compacted stress, so a lot of cities have planted 10-20% of the trees planted along the streets, are ash. You might remember, 30-40 years ago, there was a disease that’s still here in the country, it’s called Dutch elm disease, that killed almost all of the elm trees in the country, or a large part of the elm resource. And so as these cities lost these elm trees, they had to replant the streets to something. And in most cases, they replanted using maple or ash. And so in a lot of cities, there are a tremendous number of ash trees planted along the street. And in the cities like Detroit or Ann Arbor, right now, the same cities that lost all of the elm trees along the streets, 30-40 years ago, now the same thing is happening with this Emerald ash borer, it’s going tree-to-tree-to-tree, and the trees have been killed. ”

Haack said that it’s not known how it came here, but it’s suspected that it came here from some of the Asian countries that we trade with. There are a lot of insects and disease organisms that can hitchhike inside the food products that we ship each other. In this case Haack thinks that it came from some of the wood pallets or wood crating that’s associated with some of the products that we buy. It’s native to several countries in Asia such as China, Korea, Japan, and little parts of Russia and Mongolia. It could have come from any one of those countries. The research project that Haack’s conducting now involves acquiring beetles from these other Asian countries, then compare the DNA structure of the Emerald Ash Borers of the U.S. and Canada. And so the North American Ash Borers will be compared to the beetles that are collected in various Asian countries, and see where it matches most closely. There’s probably more than a dozen people involved in these studies from various universities and federal laboratories. Some of the studies that Hack is involved with now cover aspects of looking at different kinds of insecticides and possible injections to the tree to kill the larvae, or to kill the adults that feeding on the foliage. He’s also looking for attractants as way to lure the beetles into a trap. There’s also studies being conducted looking into the dispersal capabilities – how far can they fly – so that it can be determined how far they can spread. Host range studies are being conducted too; trying to find out what different tree species this insect can attack. Hack says,

“That’s interesting because this beetle is found in different countries like Asia, and, in China, the beetle only attacks ash trees. In Korea, it attacks ash trees and elm trees. And in Korea, it attacks ash trees and elm trees. And in Japan, it attacks ash, elm and walnut. So we were actually quite worried, because in the U.S. and Canada, we’re only finding this beetle attacking ash trees. So, right not it’s behaving most like the Chinese version of this beetle. So right now, we’re doing some studies to look at the host range, wondering, will it attack more than simply ash.”

RH: The beetle was first officially detected here in Michigan back in June of 2002. But it had probably been here for 5-10 years before it was actually discovered. But it was simply overlooked, or no one really just noticed the beetles, they noticed the trees dying, but then finally a series of people looked and saw some of these beetles and brought them to the tight people to get identified. And, that was quite a challenge too – the beetles eventually had to go not only to the experts in the United States, but we sent it to one of the world experts for this group of beetles all the way over to Slovakia, in Europe. And once we knew that we were dealing with a foreign pest, then we contacted our colleagues in various Asian countries and got some more information from them. But once we started looking at the situation in Michigan, we realized that we really had a problem on our hands – in that there were not only thousands, but potentially millions of trees that were already infested. And based on surveys that were conducted here in Michigan, they estimated that as of last year, there were probably already 5 million trees that were infested or killed by the Emerald Ash Borer. But Michigan alone has somewhere between 700 to 800 million ash trees statewide, and nationwide we probably have somewhere between 7 and 8 billion ash trees in the country. So it’s a real common tree.

ES:

RH: I think I would say that the problem has certainly reached the outbreak levels, or epidemic level. And, as I mentioned before, I think that the beetle has probably been here for five to ten years, but probably for those first five or six years it was just slowly building its population. But now it’s reached these levels where there’s just millions and millions and millions of beetles in southeastern Michigan. And in some of the trees that we were looking at this summer, we’d see dozens if not hundreds of these beetles crawling on the bark surface of these trees laying more eggs, so there were tremendous numbers. And the populations are not going to go down anytime soon. There’s very few natural enemies that are attacking this beetle. I’ve found several natural enemies, but they’re not removing even one percent of the pest population. And so if we don’t find effective controls or a way to manage or contain the population – then we see this insect moving nationwide throughout North America, and potentially removing all the ash trees. A lot of us are saying that this appears to be almost like a new type of Dutch elm disease – but now it’s a beetle attacking the ash trees. Once again, when I say ash trees, there’s more than 20 species of ash in the country. But here in the Great Lakes region, we have probably five or six native species of ash growing here, and so far the beetle seems to be able to attack and kill all those species. So we’re making the assumption that it probably will be able to spread throughout the country and successfully attack all the different ash species in North America. We hope that doesn’t happen, so part of the host range study that we’re doing – we’re bringing in other species into Michigan and planting them to see if they’re susceptible to the emerald ash borer.

As a follow-up to one of the earlier questions, when I say we, it’s kind of like the generic we, I mean, I’m involved in some of these studies, but there’re also some of the cooperators at the various universities that are doing the bulk of the work. But we’re also working on, as I said earlier, some of the genetics studies, trying to look at the origin, the country of origin it is, in Asia. And we’re doing a variety of studies trying to see how does chipping wood, or removing the bark of infested trees, does that effect the survival of the larvae, because some of the trees that are infected are very valuable trees, and people are asking – can we move the trunks of these tree to sawmills, or if we remove the bark, is it safe to move the remaining portion of the tree? And then, the whole firewood industry is being affected now. Because in the quarantine counties, they can’t move firewood and, so we’re looking at – does the beetle survive in firewood, and what times of the year is it safe to cut firewood, and what times of the year isn’t it safe. So there’s a whole series of questions like that. There’s a quarantine right now (summer 2003) for both the state of Michigan and the state of Ohio, as well as in Ontario. In Michigan and Ohio, the state quarantines were stopping, or restricting the movement of firewood or ash nursery stock, ash logs. So all of those kinds of materials can’t be moved outside of those infected counties.

ES:

RH: The reason it would be valuable to know the origin of the beetle would be, on the biology side, in case you want to go to the country of origin and look for natural enemies of the pest insect. So there’s actually, others and we have made contacts in China, Korea, and Japan to look for natural enemies. And there are surveys that are going on right now in China looking for natural enemies. And usually, if you can determine what the origin of the pest is, that’s the best place to look for natural enemies, because they’ll be synchronized and adapted to each other. And, another reason is, if you could identify which country a pest came from, that might help you in targeting closer inspection of products that are coming in from that country, or you might be able to learn more about the pathway as to how the insect could have entered that country, so you can slow that process or correct that process. So there’s a regulatory issue as well as a biological issue. And also, as to if there’s a problem in China, from the literature that we have and the contacts that we’ve made in China, the emerald ash borer is native to China, and it has small outbreaks, but usually the outbreaks are infrequent. And so it’s considered a pest, but an occasional pest. But it’s usually in times of drought in China, or times of environmental stress that this insect in increase into outbreak levels. But some of the Chinese reports say that this beetle can kill large areas of ash forests during outbreaks, but it’s usually precipitated by some sort of environmental stress like drought. Typically, it appears that the insect is not a problem. And that’s probably because, again, during evolutionary time ash trees in Asia and the emerald ash borer have evolved together, and they’re in some sort of balance. So in Asia, what puts it out of balance would be a stress situation such as drought. But here in North America, it appears that our ash trees have never seen an insect such as this. So we don’t have a comparable insect that is attacking the trunks of ash trees in the same way. And, so, our trees have never had to evolve these defenses and have never come into balance with this insect. So it comes into North America, and almost all of the ash trees that it encounters just don’t have the natural defenses, or don’t recognize this insect as a pest. We need more studies to prove this, but it might not be reacting quickly enough to the larvae. So when the eggs are laid in the bark surface, and the larvae tunnels through the bark, the tree doesn’t recognize, it doesn’t create a wound response, or it doesn’t try to protect itself quickly enough, so as a result, the insect is successful. It’s something that we see quite often.

One thing I was just going to mention though, in talks that I’ve given where I make statements like – there’s all these exotic pests coming into the country, one thing that we should remember is that, basically every country in the world is guilty of sending pest organisms to other countries. So, in most cases, everyone tries to ship products that are pest free. But every once in a while, material that is infested is used in international commerce. And these insects and diseases are hitchhikers and every once in a while they can find a habitat or a host tree that’s suitable to them, and then they’re successful in becoming established in a new country. And if you go to Asia, there’s several North American pests that are successful there that are very damaging. And, we have North American bark beetles and a whole series of insect problems in China. So, sometimes, I’ll give a presentation, and I don’t try and make it sound this way, but people can sometimes think that it’s a one-way street, that all these other countries are sending pests to the United States. But also, some pests are moving from the United States and Canada to other countries as well.

The following person was interviewed for today’s program. Our thanks to:

Robert A. Haack
Research Entomologist
USDA Forest Service
North Central Research Station