controlling lily leaf beetles, with u. of rhode island’s lisa tewksbury
I GET A LOT OF QUESTIONS about insect pests, but not just familiar opponents like cucumber beetles or squash bugs and Japanese beetles. In recent years, I get more and more questions from a widening region about a very beautiful but very naughty pest called the lily leaf beetle.
Its story – how it got here, and what it’s doing and what is being done about it — is also the story of the unwelcome arrival of other invasive exotic organisms that have come to our shores unexpectedly, and found no natural predators or other mechanisms to keep them in check.
I got a 101 on the beetle from Lisa Tewksbury, manager of the University of Rhode Island’s Biological Control Lab in Kingston, where she coordinates research on the lily leaf beetle among other invasives. Learn what’s being done by scientists seeking solutions other than chemical herbicides or pesticides, and what you can do in your own yard if you have them, too.
Read along as you listen to the August 21, 2107 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).
lily-leaf beetle q&a with lisa tewksbury
Q. Before we get started on the lily leaf beetle specifically, can you tell us a little about the lab?
A. The lab was built in 1994 as a biological control quarantine facility, to enable us to do some research with insects from Europe. I work with Dick Casagrande, an entomology professor at the university, and he had been doing some work with potato beetles, and looking at insects that might help control that.
They had wanted to bring back some potential biological control agents, something that could help control the potato beetle, from Mexico. They had done a lot of research on those insects, and needed a facility to keep doing that work. In the meantime, what started to happen is that there were many new invasive weeds coming into our area, and people were requesting that we start to research those.
Q. Purple loosestrife is on the list?
A. Yes. Purple loosestrife was one that I worked on for maybe 20 years but I’ve moved on…
A. …because we feel like we have done quite a bit to get the insect that feeds on purple loosestrife into Rhode Island and it’s spreading by itself now.
Q. So that’s what biological control is—and maybe you can explain it to us. Does that mean it’s a live agent, like that insect you just said, as opposed to using say an insecticide or herbicide?
A. Yes. That’s exactly what it means. And what we tend to do is specifically called classical biological control, so what that means is that for an example, with purple loosestrife—it wasn’t introduced here exactly accidentally, but was introduced as a medicinal plant and because it has a beautiful purple flower. So it starts to spread and it becomes an issue, and people go looking for and organism in its native range that could help control it. [Lab photos above from U.R.I. Biocontrol Lab.]
They actually found that there were many insects in Europe that feed on it. So then they begin to do research to find out which ones are the most safe—meaning they only feed on purple loosestrife—and which ones are most effective, that cause some sort of damage to the plant.
And then those are introduced into North America. So that’s classical biological control, and the idea is that you do it once, and it takes a lot of time and effort and research, and then you make the introduction. And then it spreads on its own, and sets up a longterm management for the pest.
Q. So lots and lots of testing first, and as you say, it’s not an overnight solution by any means.
A. No. It averages about 10 years, sometimes more than that.
Q. So: The lily leaf beetle. What is it, where did it come from?
A. That came from Europe, though the beetle is also native to Asia. But they think that it was introduced from Europe. It was first found in Canada in the 1940s, and then in 1992 in Cambridge, near Boston.
So that’s how we got involved. There was a young woman who wanted to be a graduate student in our lab, S.B. Livingston, and she worked with Dr. Casagrande. She wanted to learn more about the pests to start with, and then also find out more about the potential for biological control.
It kind of ended up going from her to another graduate student to myself. So that one has been from 1994 until currently.
Q. Before you got involved at the lab at U.R.I., it was already in Canada, and it had made its way to Cambridge, Massachusetts. But where is it now?
A. Just recently, the beetle has been found in Washington State.
Q. Wow, that’s far.
A. It’s also in Iowa, Michigan, Wisconsin—and pretty much all across Canada, and as far east as the Maritime provinces of Canada. Most of New England has the beetle, and it’s sort of skipped around those states, but if you take from Maine down, it kind of stops at Pennsylvania and New Jersey.
Q. I know this pest. It lives in my garden; maybe it’s been five years or so. I am on the border of Massachusetts-Connecticut-New York, the Hudson Valley-Berkshires area, so not so far from you, but a different kind of environment.
One year I didn’t have it, and then one year I did. It’s a very beautiful insect—and many insects are amazing looking—but it’s almost like a Chinese lacquer red, beautiful and shiny orangey-red.
A. One of its names is the scarlet lily beetle, so I think some people call that color scarlet.
Q. It’s beautiful, but I pick them off the plants—I go after them like a crazy person, and grab them up like I do with Japanese beetles and everybody else that I don’t think belongs. [Laughter.] And it has this unusual quality—actually, a number of unusual qualities, but one is that it makes a squealing noise if I grab it in my hand. Have you ever heard them?
A. Yes, they definitely do that, and they tend to do that more when you find them outside. We need to grow them in the lab to do our research, and after a while that goes away a little bit. We think it’s an alarm mechanism—a way of talking to each other,
It seems to be when you disturb them. One of the graduate students had noticed them all out in the field of native lilies, and it was raining and they were all coming to the top and all singing.
A. I have never seen that, but we do think that it’s used for defense.
Q. Well, it’s a very high-pitched sound; from my closed fist I will hear this very high-pitched sound from these very beautiful beetles, but who I am not so crazy about. [Laughter.] They have some rather undignified behaviors.
I always tell this to people about weeds, when they say, “How do I get rid of this weed?” I say, first learn about the life cycle of the organism if you want to try to outsmart it. Is that true with the lily leaf beetle?
A. Yes, and certainly when we are looking at a biological control, we need an organism that works with the life cycle. They have to be synchronized. People will notice that it’s late April or early May, at least in our area, and you’ll notice the beetles emerging from the ground.
They have been overwintering as adults, in the leaf litter or soil, and they come up when it gets warm enough, which tends to also be when the lilies are starting to come up. Sometimes people will find them really early, before their lilies are up, but that tends to be when they have been hoeing or pulling weeds, and disturbing the soil. But if it’s not warm enough, or there are no lilies, they will go back in. It’s just that on a warm day that they have come up to look around.
They will go to the lilies and lay eggs, which are orange and in a line, or a couple of lines—and they are usually on the under surface of the leaf. Then they hatch, and the larvae, or the immature beetle, is tiny—it looks like a black spot in the beginning. They will all be still in the egg mass. You might see them all and that’s how you know it’s the first stage. As they start to eat, they start to separate, but even when they get large, you’ll sometimes see them clumped in groups, and feeding gregariously, or in a group like that.
Q. [Laughter.] That’s a nice word for it.
A. I’m not sure all the benefits they get from it, but it does allow you to see sometimes that a lily leaf, which is like a large blade, sometimes will be gradually just chopped away, until all that’s left is this little bit up against the stem, with these larvae on it. FRASS LINK
That’s pretty typical if you see that leaf just being eaten right away.
As they’re feeding, and you get to the second stage, as they get enough food in them they have fecal material—or we call is frass for insects—and they’ll put it on their back. So even if they are kind of a lightish-green or yellowish insect, they will always look like a brown blob on the leaf, because they have this fecal material on their back. That’s another defense mechanism to keep birds maybe or other insects from eating them.
Q. [Laughter.] Well, it seems that this larval stage of this pest is extremely ill-mannered because it’s wandering around with poop all over itself. [above: Larval damage to lily foliage, photo from U.R.I. Biocontrol Lab.)
A. Nobody likes that. [Laughter.]
Q. So it’s like insult to injury, devouring your lily leaves.
A. But it’s a different kind of camouflage strategy. I’ll have many gardeners mention to me that they see these brown blobs, but they don’t necessarily know or understand yet that there is an insect under there.
A. That may be the case for something else that might eat them—that it’s not obvious that it’s not a living thing. So then when they are getting large enough to pupate, they drop from the leaves. You can often tell you won’t see the fecal material any more the frass, which has fallen off, because they’ve stopped eating for a day. And then they drop into the soil and they pupate—they form a little cocoon with the soil.
And then maybe 10 days to two weeks later, they’ll emerge out of that cocoon, and come up onto the plant as a new adult, and that new adult needs to feed for a while. So it feeds for maybe a couple of weeks, and then it goes back into the leaf litter and will stay there until next spring, that’s their overwintering space.
Q. And then the cycle repeats itself.
I want to ask you about the avenue of biocontrol that you have been pursuing in the lab, and then also what people like myself who are frustrated by these creatures can pursue on the smaller scale.
A. As I said the first graduate student spent quite a bit of time trying to understand the life cycle of the insect, and then checking out some other organisms that might have been available. Then when nothing was effective that was already here, she went on an exploration trip to Europe, to start the process of looking for insects that help control the lily beetle in Europe.
We continued that over a number of years, and there was another graduate student, Marion Gold, and then myself. In the process, we also enlisted an organization that helps do this. They’re over in Switzerland, and called CABI. They were able to hire people to go—and I always thought this sounded like a great job—looking for native lilies and then collecting the lily leaf beetle larvae off of them.
They collected many, and reared them, and came up with a list of parasitic wasps that parasitize the lily leaf beetle, some of them more through the eggs, some of them through the larvae. We began the process, some in Switzerland and quite a bit was done in our lab, of seeing if those insects—tiny parasitic wasps—would parasitize other insects. [Above, left to right: Tetrastichus setifer parasitic wasp adult from U.R.I. Biocontrol Lab; Diaparsis wasp parasitizing a larva photo by Tim Haye.]
So we tested other leaf beetles, and things like ladybugs, and all but one or two were very specific to the lily leaf beetle. That’s the information we need to go to the USDA and say that we believe this is safe, and ask for permission to release it in North America.
That was from around 1996-7-8 through 2001, and then the releases were made in the Boston area to start with, because that was where the insect had been first. By 1999 it had moved into Rhode Island and so we started making releases in Rhode Island and worked with collaborators in other parts of New England.
Q. So how has it gone?
A. It’s actually going very well. This year I had a good group of students doing another survey, collecting some larvae—mostly in Rhode Island but some in Massachusetts. Almost everywhere that they went to collect, there were parasitic wasps. So they have spread quite a bit.
In some locations, maybe it has been more recent that they have gotten there, and there are still a lot of larvae. The gardeners might not know that they are having any help, because their lilies still look pretty bad. But in others, we could find a few here and there, but the populations of the pest aren’t bad at all.
I’ve been getting more and more, as I send out my emails saying, “Would you be able to help me again this year and maybe even ail me some of these larvae so I can check them for parasitism?”—which people have been great to do over the years. But some of them send me emails say, “Well, I would, but I don’t have them any more.”
Q. Oh! I live in hope. [Laughter.]
A. Yes. So that’s the version of the good news that we have been getting from quite a few people, primarily in the Boston area and eastern Massachusetts and Rhode Island, especially northern Rhode Island, which is where we released these insects first.
Q. Have these parasitic wasps been released in other areas of the country? You mentioned Washington, Iowa, Michigan, Canada have the beetles.
A. Canada yes; they made their first releases a few years ago, and have been having very good success. We just started in New York this year, and Connecticut has been a few years ago. We have an arrangement to work with Washington State, but that won’t start till next year, but it will be beginning.
If we left it all alone, and stopped with the releases we made a few years ago, probably it would gradually be spread throughout the country as the lily leaf beetle does. But by making additional releases, we’re helping these states get going. The good news about that is that it’s going to be much easier to have successful management if you don’t wait until the pest population is huge.
Q. On the garden scale: So there I am, wondering the right time is to do what, and what tactics to use, and are there lilies they like more and less—since it’s bulb-shopping season. Is there anything tactical on a smaller scale?
A. There are a few things. We did a little bit of work with lilies and lily hybrids. Unfortunately, we haven’t published any of it. One thing is that the beetles will go to Asiatics over Orientals, if they’re growing side by side. It’s not a complete thing; they will feed on Orientals, but it’s one thing we noticed.
The other thing we were looking at was some of the hybrids. There is one called ‘Black Beauty’ that really the adults had no problem doing a little bit of feeding on, and they would lay eggs, but when the eggs hatched the eggs seemed to just die. So that’s one that we have been recommending, and that is a hybrid of uchida and henryi. Any in that sort of area, which I think might be called species lilies, seem to be a bit resistant to the lily leaf beetle. [Above, left to right, ‘Black Beauty’ and Lilium uchida from Brent and Becky’s Bulbs catalog.]
Q. Interesting. With a different pest that I got a number of years ago, the Viburnum leaf beetle, I had done a little homework and found a fantastic chart from Cornell University that showed what their order preference was as they knew at the time.
What I did was I took the ones they liked the most, and at the fringe of the property I planted a few of those shrubs—where it wasn’t in the middle of the front yard, not prominent. And sure enough, I have lured them over to their favorite dinner, and they have gotten less interested in the ones I have in prominent spots. Is there something like that?
A. I think you probably could. It hasn’t been the focus of my research, so I’m not able to give too much information, but I do know that there are preferences. I think if you were able to grow and get beautiful lilies–I think maybe if you grew ‘Black Beauty’ and ones related to that, and grew some other Asiatics elsewhere…
Q. Like in a nursery bed—it’s worth an experiment. Any other things—I’ve read some places about maybe Neem?
A. Yes, Neem is a really good material, and it’s very safe to use. One of the things that people are very concerned about now, especially with flowers that attract bees for pollinating, is that you want to be careful about using things like Imidacloprid or Merit that would certainly work against the lily leaf beetle…
Q. …and everything else. [Laughter.]
A. Yes, it would impact bees. So something like Neem oil is a good alternative to that. And you mentioned, if you have just a few lilies in a backyard, hand picking the adults works really well—or even wiping off the egg masses if you see them. If you’re someone who has 30 or more lilies, you might not have time to do that, but it does help for a small garden.
Q. Is there any relationship to where I buy my bulbs—we just talked about varieties, but…?
A. There is one other comment I’ll make. We just mentioned Imidacloprid, and I think Europe is in the process of changing this, but it might help for people to know that up until maybe a year or so ago, most of the bulbs that purchased from the Netherlands had been dipped in Imidacloprid for aphid control. So somebody might say, “Oh, I started, and for two years I didn’t have lily leaf beetles, but now they’re all here.” You were having some control from that.
Q. Is that a neonicotinoid?
A. It is.
Q. When I am going to hand pick, I get out of control in the spring cleanup, and I’m busy and I don’t notice till they are already chewing. Should I have sort of dug around earlier at the base of lily plants?
A. You can, but that’s a lot harder to do. I would just focus on when the lilies are coming up—or maybe a little of both. If it’s a beautiful warm day and you’ve gone out to clean up the garden, and you see them, definitely get rid of them. But then as the lilies are starting to come up and they’re starting to find them, try to get rid of them, because on a sunny hot day they’ll be really visible.
Q. Do they like lily relatives, like fritillaries? [Above, a crown imperial fritillary.]
A. Fritillaria is the only other genus where the larvae will develop all the way to an adult. There are a few other plants, primarily Solanaceous plants, like the potato, where the adults might feed, and do a few nibbles. People will sometimes say they see them on daylilies [Hemerocallis], but they can’t develop on daylilies. So it’s really just the Lilium.
Q. True lilies. You know I might want to mail you some little creatures. [Laughter.] I’ll pack them up carefully, I promise.
A. Yes, I have written up a little protocol so that if people want to do that, they have my address.
Q. A plain envelope is not going to be good for those guys. [Laughter.]
A. No, sometimes I get them in a plastic bag and they are a little worse for wear.
Q. Eeew. [Laughter.]
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MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its seventh year in March 2016. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the August 21, 2017 show right here.You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).