Earth & Sky

The following individual was interviewed for today’s show. Our thanks to:

Mark S. McClure
Entomologist and Chief Scientist
Valley Laboratory
The Connecticut Agricultural Experiment Station
Windsor, CT

Interview with Mark McClure:

It was 1980 or so when I first learned of a very important potential threat to Eastern hemlock, and that is the hemlock wooly adelgid, which had been present around Richmond, VA around 1951. How it got there no one really knows, although it showed up outside of an arboreteum outside of Richmond and had been moving through the mid-atlantic states primarily through ornamental settings and residential properties and so forth until it started to move into New York State. It became much more of a concern in the forest. So I was on the lookout for it when it first arrived in Connecticut in ’85. And so I was poised to begin my studies with it and that’s when the story began, really.

In 1985 it (the wooly adelgid) first arrived in Connecticut and I was very surprised that – although it had been present in the Eastern United States for some 35 years prior to its arrival in Connecticut, virtually nothing was known about this insect. Nothing had been done in the way of reseach on its biology, life cycle, how it was injuring trees and so forth here in the east. So I was really quite surprised in that. I pretty much had to start from scratch in 1985 by studying the biology, the life cycle, population dynamics, how trees were being injured, how quickly that happened and so forth. And I did that for the first five or six years or so, and it became apparant to me that during the course of those studies, that none of the native, natural enemies that inhabit our hemlock forests here in the East were opportunistic at all. They weren’t taking advantage of this new abundant potential host in the hemlock wooly adelgid. And as a result the adelgid was pretty much having its way in the forest and killing trees at an alarming rate. I did find that in the ornamental settings, there are a number of chemical tools which are effective in keeping hemlock wooly adelgid populations at bay. And so in an ornamental setting you can keep trees healthy even though they’re under attack. But in the forest, because pesticides are difficult to apply, and because there are no native natural enemies, the forests were just succuming to attack within 4 to 6 years, typically. So in 1992 I decided that a solution to the problem might be in Japan, the homeland of hemlock wooly adelgid. So I travelled there in 1992, really not knowing what to expect to find. The adelgid hadn’t been worked on in Japan. It was harmless. It was relatively rare, occured up in the mountains, and so forth. And no one really knew much about it. So I went over there not really knowing what to expect. I spent two months there in 1992 and was able to find hemlock wooly adelgid, although in very low numbers throughout the native range of two Japanese hemlock species in Honchu, Japan, and also planted in ornamental situations like in shrines and temples around the cities and so forth. And throughout those infested areas, I did find a number of predators, including a ladybird beetle that was previously unknown to science. It had never been described before, no one ever knew it existed. And I did find it occuring at quite a number of these sites. And it was obviosly a predator of hemlock wooly adelgid having a very good affect on it, a controlling effect. So, working with a Japanese colleague, Hiriyoki Susaki, we subsequently described and named that ladybird beetle Pseudoscymnus tsugae. And after having finished my studies in Japan, I was really interested in getting that beetle established in Eastern North America as a potential biological agent.

[**] Developing a biological control agent, especially an exotic one, really does demand intensive work and extreme care. The last thing we want to do is to introduce another problem into our forests.

So it took us a year and a half to study pseudoscymnus sufficiently, and to research the literature sufficiently to feel confident that – first of all – that it would have a great potential for biological control and it would be of minimal risk to the environment. And after having accumulated all of that data, for that period of time, we submitted our information to the U.S. Department of Agriculture Animal Plant Health Inspection Service, (APHIS), and they provided us with a permit. They felt that there would be no risk to the environment in releasing pseudscymnus and potentially great benefit. We started our release efforts in 1995.

Well, it was very clear that hemlock woolly adelgid was changing the face of the hemlock forests in the Eastern United States when I began work in 1985. And at that time, relatively few states were involved. It had just about made its way into the blue ridge of Virginia, was starting to spread down to the Applachians, spreading northward into New York and Southern New England. But it was spreading much more quickly now that it had occupied these areas because it was finding hemlock distribution more contiguous. It was spreading more quickly as it got into the forests. And people became very concerned. It was killing trees relatively quickly. Hemlock forests are unique in where they occur and how ecologically imortant they are. So the Forest Service got extremely interested in the work that I was doing and in the natural controls that I had developed, especially the ladybird beetle that I discovered in Japan. As I said, I started releasing in 1994, but since them, over the past eight years, the hemlock wooly adelgid has spread very quickly. It now occurs in 15 states all the way from Georgia and Tennessee, in the Smokies, all the way to Northern New England. So it’s spreading more quickly. It’s a huge problem now. It certainly is a problem of the future, as it invades the more contiguous areas of South Eastern Canada, Northern New England out to the Lake States. But certainly, the area it now occupies has is of specific concern. A huge effort is underway to mass rear and release the beetle that I discovered in Japan in hopes that this biological agent can get established and start to bring adelgid populations down to levels below which trees are irreversably damaged. So that’s the battle we’re now fighting. I would say that it has intensified tremendously over the past 10 years or so. We’re right in the throes of the battle right now.

Without getting too technical, the insect feeds on the cell fluids of the trees. It removes energy. But also during the feeding process it injects a toxic saliva into the plant. And what this does is it compromises the vascular system. The tree does not produce vessels, cells, of suffient size to transport the water it needs up into the upper crown so the tree really dries up very quickly. It dessicates, loses its needles, and that’s how it declines quickly. And if you subject those infested trees to drought conditions like we’ve had here throughout the Northeast in recent years, then that just hastens the decline. The tree is less able to get the water it needs because of the lack of water and because the adelgid feeding, trees can succomb very quickly. And that’s really what’s happened over the past several years. So hemlock stands are declining very rapidly, and the hemlock forests are changing very quickly. As the hemlocks are wiped out, other, less desirable tree species are coming in at a tremendous ecological impact.

[**] There’s always an element of risk when your’re introducing a species, whether it’s a predator, a parasitoid, whatever from a foreign land into the new area. There’s always a risk.

What we have to do is to weigh out the risks and the potential benefits relative to what’s going on in the forests with the past. With Pseudoscymnus tsugae, we really started out with looking by looking at what attributes it has which would make it a potentially good biological control candidate. And we did study it for more than a year in laboratory intensive studies, and we found that its life cycle is very closely synchronized with that of the hemlock wooly adelgid. It feeds on all stages of the adelgid, all stages of the beetle, and it really prefers to feed on hemlock wooly adelgid. It has two generations each year, just like the adelgid, it can be mass reared. It has many of the qualities that one looks for in a successful biological control agent. So that’s the first thing – it does have the qualities that one looks for. Then you have to look at what potential negative impact it might have on the environment. What you would like to have in a biological control agent from abroad is something which is very different from the native types of predators we now have. Pseudoscymnus is of a type of ladybird beetle that does not occur in North America. Therefore it doesn’t really have any close relatives here. And that would suggest that it probably isn’t going to compete with some of our native ladybird beetles and out compete them and drive them to extinction. And that’s the advantage to working with something that doesn’t really have any relatives here. That certainly was the case with pseudoscymnus. We conducted laboratory tests, host preference tests where we exposed various other kinds of potential prey items to the ladybird beetles in arenas and found that certainly it has a very restricted host range. It does prefer to feed on adelgids. It will occur on other adelgids – but adelgids by and large are considered pests, and we didn’t see that as a downside. It will occasionally feed on other aphids and so-forth, but really it doesn’t prefer them. And again, those aren’t things that are typically considered beneficial. So in its restricted host range – that was another quality of pseudoscymnus which we felt made it very minimalist to the environment. So we really didn’t see any downsides. During the course of our studies, we’ve carefully monitored this in the laboratory and in the field, and we’ve never seen any antagnostic associations, negative associations at all, with any other insects or anthorpods or what have you that are on hemlock. So we are quite confident that pseudoscymnus is of very low risk, and that there is tremendous potential benefit to our hemlock stands.

We did a number of studies, initially. We started releasing beetles in 1995. And they were small scale. The beetle is somewhat difficult to rear, in that it only feeds on adelgids, and you have to bring in adelgid infested hemlock from the field and put them in cages and put the beetles on it and keep everybody happy while the beetles mature. So it’s quite a hands on effort. And as a result for the first few years of our effort, we only had a few thousand beetles to release in any given area. So from 1994 to about 1997 we’ve released beetles in lots of about 2500 in any given forest and conduct our studies that way. We basically had several studies in Connecticut, about 4 or 5 study sites in Connecticut. We have one in New Jersey, which was about 1/2 down the distribution of hemlock adelgid, and one in Virginia – toward the southern end of the range. And we wanted to do that to see how well the beetle was able to control adelgid populations across the distribution from North to South. And the results of some of those early experiments – some of them in cages, some of them outside of cages – were very encouraging. Where we did release beetles, those trees had 50 to 85% fewer adelgids after a single season than did similar trees with similar infestations and areas where beetles were not released. So we were bery encouraged and excited about this, as was the U.S. Forest Service. So, following 1997, we donated a sister colony of ladybird beetles to a mass rearing facility in Trenton, NJ. And they started mass rearing them for distribution to other states. And that started a multi-state release project, wherin we’ve now released more than 1 million beetles in over 100 sites in 15 states. And we’re coordinating our sampling efforts so that we can continue to evaluate how well the beetle is controling hemlock wooly adelgid populations from Georgia to Maine. It’s just a difficult process that requires a lot sampling and a lot of hemlock crown health classifications to follow the health of trees. And those trends are really being affected by a number of different factors, not only being the presence or abscence of beetles, but also by the weather, the draught we talked about, cold weather conditions that sometimes will kill adelgids during the winter and so forth. But in large, the trends have been very positive. We’ve seen trees that have been severely injured recovering nicely over the past 2 or 3 years, although we can’t attribute it neccessarily entirely to the beetle, the trends are very favorable at our release sites.

Well, the actual sampling involves marking individual trees and following their health from year to year, and also monitoring those trees for the prescence of adelgids and what their population densities are and also the prescence of beetles and how well their numbers are increasing and how well it’s spreading. And that’s how we actually follow trends at individual sites. We obviously have a greater demand for the beetles, but we’re getting them out in much greater numbers, so we’re increasing our ability to really what impact the predators have in the adelgid populations thoughout the range. That’s an ongoing process in order to determine, really, how well things are going we have to look at how long term, from year to year. And it’s discouraging, because in some areas, the poor sites where hemlocks are under severe stress with draught and so forth, trees are declining even though beetles are present, but where we do have our better site where trees are growing under fairly good conditions, that’ where we’ve seen our greatest success.

One of the most surprising, rewarding thing for me has been to really be there from the beginning and to see the whole thing develop. I mean early on, nothing was known about the adelgid. And after several years of working with it, determining it’s biology, and how to control it, and ornamental settings and so forth, and then having gone to Japan not really knowing what to expect there and that obviously resulted in my finding a beetle that had great potential and now has really aroused the excitement of a lot of people here in North America and is being mass reared, and lots of research money is being poured into the development of that biological control agent, I think that has been the most rewarding and surprising aspect for me. I mean I’ve kind of been there from the beginning so it’s developing into something which may eventually be a solution, I would hope at least a part of the solution to the hemlock wooly adelgid problem and may allow hemlocks to remain as a functional part of our forest’s here in the East.

Well, it varies from state to state. As you move northward and southward, it changes in terms of its importance to the forest. Here in Southern New England anywhere from 10 to 20% of our forest trees are hemlock, but as you move into Northern New England, and into Southeastern Canada and into the lake states, it starts to comprise 50-60% of the forest. Where it occurs, I think is the reason why I think why it’s so important ecologically. It’s a species that is very shade tolerant. It can grow in shallow soils on steep slopes. It often occurs along rivers and streams and along lakes and so forth. And it really provides a dense, moist habitat for a number of animals and plant species and really provides a lot of protection during the winter for deer and other wildlife species – several species of birds, for instance, are associated only with hemlock. And so I think in terms of protecting our waterways and providing habitat for those animals and plants that depend upon that moist, cool environment, I think that’s the main importance of hemlock.

…. It’s very difficult to work in the forest environment, a three dimensional forest, and sampling tools oftentimes are two-dimensional, working on the forest floor. So it’s difficult following the movement of the forest floor with predators, and looking at the upper crown, and so forth, of trees. And we’re starting to get a handle on that now. We’re doing some work out of bucket trucks to get up into the upper parts of trees and also felling some trees to get a handle on what’s going on up there. So that has been a major obstacle, just the sampling effort to try to monitor the movement of predators and to determine just what exactly is going on in the forest. And hand-in-hand with that is the major challenge of trying to evalutat specific factors in how they’re impacting wooly adelgid populations. We can see the overall trends, but to try to sort out which factors are mostly responsible for the trends we’re seeing – whether it’s overwintering mortality to the wooly adelgid, or whether it’s draught sensitive trees, whether it’s the beetle at work or whatever else, those are very challenging things as well and are certainly obstacles. And last but not least, the problem of the rearing of the beetle. It does require lots of hands-on effort to bring in live material of the adelgid and to follow them through development. And considering the face that the ladybird beetle is only the size of a poppy seed – it’s very small – it takes an aweful lot of manipulation, an aweful lot of labor. And that’s why it’s a very expensive proposition rearing these things. And we now have two mass-rearing laboratories that are rearing these beetles for distribution and we’re getting over some of the major challenges. We’re trying to streamline that effort now and that has also been a challenge.

Well, certainly there are different ways to management of introduced species, or invasive speciesin our forests. Gypsie moth has been a perfect example of a species that arrived here in the early part of the 20th century, started to spread to our Eastern forests, and really, an army of scientists tried for decades to control gypsy moth with very little success, introducing this natural enemy and that one, trying this fungus and that bacteria, cultural methods and what have you. And it would just go through its cycles and pretty much deneuter the forests along the way at its own schedule. It wasn’t till about 10 years ago that a fungus that had been introduced intentionally several decades ago and disappeared. But now this fungus had appeared 10 years ago and started to work its magic and the fungus had spread throughout the gypsy moth infested area, and ultimately – I think – has become an extremely important and successful biological control agent. And gypsy moth outbreaks are now a rarity and I think that those mass outbreaks are a thing of the past. I think that’s the best example I can come up with in recent history of a biological control agent that’s really now starting to manage an exotic pest for decades that was almost impossible to deal with. I think that biological control is a lasting control. I think there are chemicals, and that we can continue to spray chemicals for management, but that’s going to be an annual committment, and its not environmentally friendly, obviously. But I think if you can come up with safe biological controls and get them established, they’ll take care of themselves and strike that balance which evolved in their homeland. And that’s what we’re doing here with hemlock wooly adelgid.

[**] This ladybird beetle, Pseudoscymnus tsugae, I think co-evolved with hemlock wooly adelgid in Japan. It’s a tremendous system in Japan. Neither one wins – there’ll always be adelgids there, there’ll always be beetles there, there’ll always be hemlocks there and they’ll all live in harmony. The problem was that when the adelgid arrived here it found itself on a hemlock species that was tremendously susceptible, had no defenses. The adelgid was building its populations and killing the host.

The challenge is to now strike up that same balance here in North America those effective natural enemies from Japan, I think with those Pseudoscymnus introductions we’re well on our way to doing that. I think it’s a numbers game at this point. I think that we have, literally millions of adelgids out there and thosands of beetles. And it’s going to take time for those beetles to build their numbers up to the point where they’re going to start managing adelgid populations. Perhaps this ladybird beetle won’t be able to do it alone, it may require the introduction of others as well. But hopefully, in time, our biological control efforts will be fruitful in saving the hemlock. Again, there are other ways of managing the forest with cultural manipulations and genetic manipulations of hemlock trees to see if we can breed for resistance, and so forth. But I think that biological control, among the different controls that we can contemplate, is the one that could provide lasting, effective control with minimal effort once it’s established.

Well, I think the question that I get all the time is, when are these beetles going to be available, and are they available and so forth. Unfortunately at the present time, it is still experimental. The beetles are not available commercially, but I anticipate that within a year or two they perhaps will be commercially available if things continue to go well. I think that’s a message that most people will be most interested in hearing.