161 - Kate LeCroy- Exotic Mason Bees


Andony Melathopoulos: [00:00:00] A few episodes back we had a fascinating show with Josh Vlach, from the Oregon Department of Agriculture, talking about the importance of keeping invasive arthropods out of Oregon as a way to improve pollinator health. And one of the things that he mentioned was keeping exotic bees out of the state. Now, there hasn't been a lot of data sort of looking at the association of the growth of an establishment of some of these exotic bees on native bee communities until recently. You may have heard in the news, there was a fascinating study done in Virginia and Maryland tracking exotic mason bees, and the associated changes in some of the native bee communities.

[00:00:42] And I'm so pleased today to bring the author of that study, to talk to you. Kate LeCroy is a PhD candidate at the University of Virginia working out of the Roulston lab. And it's a fascinating episode in terms of, how you bring such data sets to bear on [00:01:00] problems like this, and some of the challenges of using data to make these kinds of interpretations of impact. It's also fascinating because it's the first episode we've ever had that includes a Dolly Parton playlist. So, you won't want to miss this episode.

[00:01:14] The other thing to point out is that, Kate is going to be talking this year at the annual Orchard Bee Association meeting. One of the best meetings that I attend every year, it's going to be on Friday, December 11th, 9:00 AM to 1:00 PM Pacific Time. You can register at the Orchard Bee Association meeting. There are going to be some fantastic speakers there, but also just a chance to stay in touch with what's going on in the orchard bee world, orchardbee.org - register today.

[00:01:41] And without further ado, here's Kate LeCroy talking about exotic mason bees today on PolliNation.

[00:01:51] Okay, well, I'm so excited to have you on the show today. Welcome to PolliNation.

[00:01:56] Kate LeCroy: [00:01:56] Thank you for having me, Andony.

[00:01:59] Andony Melathopoulos: [00:01:59] You know, lots [00:02:00] of gardeners and orchardists have talked about cultivating mason bees. We've had lots of shows on, cultivating mason bees. Can you tell us a little bit about the genus Osmia, particularly the species that you have in Virginia and Maryland, where you did your research?

[00:02:14] Kate LeCroy: [00:02:14] Yeah, certainly, mason bees are in my opinion and hopefully yours, are really cool. And mason bees are in the genus Osmia and they usually nest in hollow cavities found in nature. So that could be little rocky crevices and outcrops or abandoned insect burrows from beetles or other ground nesting bees. They nest in snail shells or pine cones, and even in a rolled-up newspaper. If you build it, they will come.

[00:02:48] And they earned their name, mason bee, not by joining a secret society, but by using materials like mud or chewed up leaves make little walls inside their nest. And we've got around [00:03:00] 20 or so mason bee species in Virginia, and some of those are native. Most of them are native, but we also have some exotic mason bees in Virginia, including Osmia cornifrons and Osmia taurus.

[00:03:16] Andony Melathopoulos: [00:03:16] Before we get into the exotic bees - I often think of mason bees as being, bees that fly in the spring. Is that necessarily the case with the Osmia fauna that you have up there in the north east?

[00:03:32] Kate LeCroy: [00:03:32] Good question. So a number of our mason bees do emerge in the spring. We do have bees that are active in the later summer seasons. I think my favorite pollinator species Osmia texana is active later in the summer around July.

[00:03:53] Andony Melathopoulos: [00:03:53] Okay, fantastic. Let's get back to the fact that you mentioned that there are a number of species that are [00:04:00] native, but that some were exotic. Can you explain who these exotic mason bees are and how they got to your region and maybe this larger issue of, you know, how these bees are getting moved around the world?

[00:04:14] Kate LeCroy: [00:04:14] Yeah, certainly. So with mason bees, some mason bees have a history of being studied and managed for orchard pollination, and some mason bee species are introduced to areas where they didn't previously exist. In fact of all the bees species, most bee species that we know of are introduced to North America, they're all cavity nesting bee including mason bees.

[00:04:42] And two mason bee species introduced from Asia have recently naturalized in the region. And the Japanese horned-faced bee is Osmia cornifrons. And that's a mason bee that was intentionally introduced from Japan [00:05:00] by the USDA, the United States Department of Agriculture. And it was introduced in the 1970's for crop pollination services, such as for apple orchards.

[00:05:11] In 2002, another mason bee from Asia, Osmia taurus was first documented in the United States and we first found it in West Virginia. And we don't know how it got here. There's no record of it being intentionally imported. We know that most bee species that are introduced intentionally or unintentionally are cavity nesting bees that are introduced in North America. They often come nesting inside cargo unsuspectingly or in lumber for furniture making. But this is how oftentimes species are introduced either intentionally or unintentionally.

[00:05:50] Andony Melathopoulos: [00:05:50] We had an episode a while back, where someone was describing alfalfa leaf cutting bees and the way that they were brought over and they [00:06:00] seem to have been introduced, accidentally, but then somebody figured out they were getting high yields for alfalfa seed crops, and then they started the cultivate them. It's been going on for a while, that was back in the fifties, at least when that happened.

[00:06:13] Kate LeCroy: [00:06:13] Yeah! Jim Cane and Theresa Pitts-Singer have a cool, article about alfalfa leaf cutting bees.

[00:06:21]Andony Melathopoulos: [00:06:21] It is a great article it really is one of those species that there was research on it, but there's kind of a grassroots sort of taking up of the bee. The whole cultivation is a fascinating story. That's one example where people will say, "oh, the introduction" and I imagine in the first case with coronifrons, it was introduced specifically for the purpose of pollination. But in many cases, these bees are just coming in, every year, another one's landing and it takes off.

[00:06:58] I [00:07:00] haven't seen a lot of research looking at the effects of these introduced bees on closely-related native species. Can you explain how you kind of came to this research question and, how you were able even to ask the question about these negative impacts? When I imagine the impacts happen over a span of a decade or so, and you're doing your PhD work. So how were you able to even approach this question?

[00:07:24] Kate LeCroy: [00:07:24] Yeah, that's a great question Andony, and really figuring out if one bee has a impact be that positive or negative on another bee is so hard to measure, in part, because bees move around really fast. So documenting any kind of competition among bees, is really hard compared to say plant competition. But, I always find myself wanting to look at patterns and confirming patterns before I start thinking about what produces the patterns.

[00:07:59] So, [00:08:00] what I really wanted for my PhD was to find and confirm patterns about bee decline, because the literature is really sparse. The literature is really sparse when, you're looking at impacts of exotic bees on native bees or introduced bees on native bees. It's pretty sparse, but in my place, I wanted to find a pattern first that held true. And then start elucidating, any mechanism that might produce that pattern or that could be responsible for producing that pattern.

[00:08:36]Andony Melathopoulos: [00:08:36] Okay, that's great. That first point you made about how difficult it is to track these patterns, because the patterns will take place over a long period of time. The bees are flying around and with wild bee communities, they go up and down. One year they're good, one year they're not. It's not like a managed species where you're trying to maintain a steady level over time. [00:09:00] So how on earth were you able to measure this impact? This question would take a lot of area and a lot of years. How did you manage to even ask this question in a PhD?

[00:09:13] Kate LeCroy: [00:09:13] Yeah. So I am very lucky in terms of standing on the shoulders of giants. There've been a lot of collection efforts and efforts to track changes so far in the region I was interested in, which is the Mid-Atlantic United States. So that includes West Virginia, Virginia, Delaware, Maryland, as well as Washington DC. And there have been records of where these mason bees are and how frequently they were captured in a given area.

[00:09:49] And a good opportunity to look at that change over time could be using data from pan traps. And pan traps in the Mid-Atlantic they've been [00:10:00] used to catch lots of flying insects are attracted to these colorful plastic bowls or cups. And they are essentially plastic bowls filled with some kind of preservative solution or soapy water to catch the flying insects.

[00:10:14] These insects will die in the solution and a collector will scoop them out of the bowl to clean and identify the insects that they're interested in. And I spent some pretty frequent pan trapping activity throughout the Mid-Atlantic United States since the early two thousands, especially in Maryland, Virginia, Delaware, and West Virginia. A lot of those efforts have been coordinated by Sam Droege at the US Geological Survey. And he has this wonderful community of volunteers and citizen science participants all over these states. Sam's pan trapping dataset continues up to today. So I think the earliest records might be in [00:11:00] 1999 when I was nine years old and he's still going getting a whole community involved in monitoring.

[00:11:10] Andony Melathopoulos: [00:11:10] A funny anecdote is when Sam came for a holiday in Oregon, he brought pan traps with him and then, it had to be like three or four months later, I got these pizza boxes full of pinned and labeled bees. And I was like, "holy smokes, how did he do that?!"

[00:11:27] Kate LeCroy: [00:11:27] Oh yeah, he's notorious for his little Caesar's pizza boxes of bees. And he'll give them to, seventh graders and grandparents and he doesn't keep them roped up in museums for everybody, who's unable to go back into the back of a museum collection. He gives these pizza boxes out to classrooms and everyone. So it's really bringing the bees to everybody.

[00:11:55] Andony Melathopoulos: [00:11:55] But I guess before those pizza boxes go out to everybody, that data is collected and captured. And so [00:12:00] there's years of data that has been captured. So anytime an Osmia species sort of flew by one of these traps and landed, it got captured in a dataset. And I guess that's what you had. You had data sets from across the region. They weren't specifically looking for Osmia, but Osmia were landing in them.

[00:12:20] Kate LeCroy: [00:12:20] Yes, exactly. Andony. So we utilized Sam Droege's dataset where they cleaned and, pinned and identified those bee species. And there were a lot of other bees and wasps that were in those pan traps that are not just Osmia. So another great data set I utilized was from Grace Savoy-Burke and Debra Delaney at, University of Delaware. Grace and Debra coordinated, an extensive pan trapping project in the same general region in 2014 and 2015. And I also conducted a citizen science program with folks doing pan [00:13:00] trapping all over Virginia in 2017 and 2019.

[00:13:04] Andony Melathopoulos: [00:13:04] I really, I really love that idea as well, just, in terms of when people do these kinds of surveys, they can be used years later for all sorts of questions also just getting the infrastructure in for doing the surveys can be so helpful. Years later when, somebody has a really good question to ask of it.

[00:13:25] Kate LeCroy: [00:13:25] Yeah. These pan traps, they caught all kinds of bees and wasps and, to be completely clear, not everybody, probably no one who was putting out these pan traps thinking exactly "oh, how are the mason bees changing in how often I catch them?" So there were plenty of variation in how people put out these pan traps. For instance, let's say they're in West Virginia and they set out perhaps 15 bowls and they'd leave these bowls out for [00:14:00] two days. So that's a sampling event in West Virginia that use 15 bowls for two days and they collected certain number of bees.

[00:14:09] We would just pull the data for mason bees and look at that. But let's say there's another sampling event that's in Delaware and they put out nine bowls, not 15 and they leave them out for seven days instead of two days. And then another person in Maryland just set off 50 bowls for one day and on that day there was really bad weather. So how do you standardize what they did? And how do you make conclusions? Especially year to year? It's really hard, it's not a trivial problem.

[00:14:45] Andony Melathopoulos: [00:14:45] Can you tell us a little bit about it? In the paper that was recently published, on your work, you describe how you were able to deal with these inconsistencies. It was just really fascinating because I imagine other researchers, have the same issue [00:15:00] of, taking these data sets and trying to sort of pull them together so that they can make them meaningful. Tell us a little bit about the steps that you took.

[00:15:06] Kate LeCroy: [00:15:06] All right. So it's definitely not a trivial problem and we wrangled a lot of data. So one way we did this was filtering out sampling events perhaps that noted bad weather. Bad weather events could be a reason why you don't see a certain bee, not because it wasn't there, but because the bad weather had bad flying conditions. And we also filtered out events that didn't use all three colors of the standard bowl colors for pan trapping. So they had to use blue bowls, yellow bowls and white bowls. And there are lots of sampling events that only used one or two of the colors and some records didn't even have the notes about what colors were used.

[00:15:56] Andony Melathopoulos: [00:15:56] Oh, and I suppose the reason that's significant is that [00:16:00] the bees may have a bias towards a certain color. So if you only had yellow ones, it might skew the results slightly.

[00:16:07] Kate LeCroy: [00:16:07] Right. There may be certain groups of bees that are more attracted to certain colors. And, generally figured out that across all times of the day, the colors attractiveness can change given what color it is. So they know that blue, yellow and white are generally fail safe combination to get as many bees that would come to pan traps.

[00:16:31] Andony Melathopoulos: [00:16:31] Okay, so you filtered those out and you looked at the notes and "oh this is a bad weather day, I'm going to take this out, that doesn't represent the sample."

[00:16:41] Kate LeCroy: [00:16:41] Yeah and overall, there were about 350 of the sampling events that didn't use the right colors. And, that was about 3,000 mason bees assessment records that we couldn't use in the analysis.

[00:16:58] Andony Melathopoulos: [00:16:58] So, I remember reading in the [00:17:00] paper at this fascinating situation where you had one trap that had just an inordinate number of one species in it, that you had to filter out because it was just so unusual.

[00:17:09] Kate LeCroy: [00:17:09] That was bizarre. There were, 550 or so mason bees in a single day and the next largest event was a 35 day catch that had significant maybe 80 specimen records. So it was a lot, it was just very unusual. So we left that one out, but we were transparent. We did run the analysis with it and put it as a supplementary analysis to show that it didn't change for that particularly weird event.

[00:17:43] Andony Melathopoulos: [00:17:43] So how many bees in total?  This was 15 years of data. When you brought it together and how many bees are we roughly talking about?

[00:17:55] Kate LeCroy: [00:17:55] Yeah, we're talking about around 6,000 specimens of mason [00:18:00] bees and, over about 1,100 sampling events.

[00:18:04] Andony Melathopoulos: [00:18:04] Okay. Fantastic.

[00:18:05] Well, let's take a quick break. I want to leave us on a cliffhanger. It's like, "hey, if you want to know what happens next, join us after the break." So let's take a quick break and we'll regroup and, find out what you found in all those 15 years of data with these mason bees in Virginia and Maryland.

[00:18:23] Okay, we're back, you know, at the break, I always love the breaks cause we get a chance to debrief a little bit. And one of the things that we didn't talk about in terms of, making the dataset fit, was not just, whether the traps are the same color or bad days, or kicking out these extraordinary bee catch events, but also other factors. Can you walk us through some of the other things that go into taking a data set like that and making it into something that's apples and apples?

[00:18:54] Kate LeCroy: [00:18:54] Yes. And yes, that is really important to have [00:19:00] some amount of data that you can compare more as equally as possible or as best as you can. So, one thing that some sampling events did not have, was the same number of bowls put out in each sampling event. Some might have set out five bowls for their pan trappings, other sites set out 50 bowls. And, so how do you account for differences in number of bees that way? And there's also the number of days that they set up these pan traps. Some will be just for a day, others will be for 15 days. So how do you standardize these different data?

[00:19:44] And the way we did that was standardizing it in our statistical analysis, where we multiplied the number of days and the number of bowls and created bowl days and that is what we’re calling our offset variable in our [00:20:00] analysis. And the other element was, space. So the Mid-Atlantic is a large swath of space. It's not just one field station with a plot to look at bees over time. And that has exciting, context to make conclusions about a larger area. But it's also difficult to say, that you were able to document this over time significantly.

[00:20:26] Andony Melathopoulos: [00:20:26] Well, I know like people are familiar with it, we've had Rich Hatfield on from Xerxes doing the Pacific Northwest Bumblebee Atlas, where they gridded out the state and kind of evened out the sampling effort. But I imagine when you have a historic data set, you can't do that. You're sort of opportunistically picking data where somebody ran a study. So how do you standardize that?

[00:20:47] Kate LeCroy: [00:20:47] Yes. So we worked really hard pre-analysis and post analysis to make sure we accounted as best as possible for spatial [00:21:00] variation and spatial what we call auto correlation. Mini spatial structure left in the analysis could give us concern that our estimates are not valid or that there could be problems in interpreting them. So, we utilized, a clustering strategy and it was based on the estimated forging distances of mason bees. And so if these sampling events were very close to each other within the foraging distance of a mason bee, we clustered them. And sampling events that were in the same year we pooled all of their records data together and we added their bowl days.

[00:21:52] Andony Melathopoulos: [00:21:52] Oh great. Because I guess the issue is you could inflate the numbers if you have a bunch of bowls that are very close together, it gets [00:22:00] very inflated because there's just so much sampling activity there. But rather you could say, well, they're kind of the same unit of area because the bees are in those bowls could be from the same nests or something and so then you just kind of make it a unit together.

[00:22:15] Kate LeCroy: [00:22:15] Yeah. So, if there's a lot of sampling events around Baltimore, Maryland, spoiler alert there were. So we're going to cluster those, we're going to, pull those data so that we don't get just tons and tons...

[00:22:29] Andony Melathopoulos: [00:22:29] So, Baltimore dominates the data set.

[00:22:32] Kate LeCroy: [00:22:32] Yeah, so we don't want that to happen. So we cluster those sites and standardize it that way.

[00:22:39] Andony Melathopoulos: [00:22:39] Fantastic. Okay. We teased that we were going to get into the results, but we're really going to get into the results now. So what did you find? Were these exotic bees having a negative impact on, the native mason bees that were there?

[00:22:55] Kate LeCroy: [00:22:55] Yeah. So what is interesting to me is that in [00:23:00] this study, I didn't find any causal linkages of one exotic be impacting a native bee. But what I did find were interesting patterns and we found that in the Mid-Atlantic we were able to analyze eight mason bee species. Six of those mason bees are native species and two are the exotic, cornifrons and taurus. And we found that all six of the native mason bee species that we caught were on average, caught less and less every year in their raw numbers and significantly so. At the same time, in those 15 years, one of the exotic mason bee species Osmia taurus is soaring in the number caught in pan traps on average each year. So the other exotic species Osmium cornifrons doesn't seem to be changing in abundance in these pan traps year to year.

[00:23:56] Andony Melathopoulos: [00:23:56] Okay, so a lot of the native [00:24:00] species are doing poorly or there's less of them showing up in the traps every year. What kind of magnitude are you seeing? What was the extent?

[00:24:10] Kate LeCroy: [00:24:10] Our native species were declining anywhere from about 9% to 16% per year in abundance. And that would mean if you think of a cumulative loss of bees since 2003 -  that would be all native species, their cumulative loss range from like 76% to 91% since 2003.

[00:24:49] Andony Melathopoulos: [00:24:49] That's really dramatic. That's a really interesting finding. You also mentioned, you had two exotic species, cornifrons wasn't in decline, [00:25:00] but it was holding steady. But you said that the second exotic species really grew. What are we talking about there?

[00:25:11] Kate LeCroy: [00:25:11] Yeah. So it was about a 16% increase per year on average, in our pan traps. And if you were to think about that as a cumulative increase, it would be an 800% jump since 2003 in abundance in pan traps.

[00:25:30] Andony Melathopoulos: [00:25:30] So that's really remarkable. It's the first finding of that kind that I've ever encountered. So it's really useful information. You mentioned earlier that you can document descriptively that this is going on, but the causation - that wasn't really the scope of the study. What questions rise in your mind in terms of like, what might be causing this? And what might be sort of driving these changes?

[00:25:55] Kate LeCroy: [00:25:55] Yes. I think that's really important and that a pattern [00:26:00] like this brings back the importance of talking about bee decline. When we talk about bee decline we often fail to tease apart winners and losers, and that's an important distinction to make when we're trying to save the bees.

[00:26:17] Andony Melathopoulos: [00:26:17] Oh, so like "winners" and "losers". Some species may proliferate, and some may decline. And when you talk about decline across the board, it doesn't capture that level of detail, which is important.

[00:26:32] Kate LeCroy: [00:26:32] Yes. Yes, exactly. And I think the factors that could be driving the patterns we're seeing, there are a few, but I'm excited to explore them, but these are just hypotheses. So one is competition for resources like floral resources and nesting resources.

[00:26:56] Andony Melathopoulos: [00:26:56] Oh, so by nesting resources, you mean those [00:27:00] twigs or pine cones, all those other kinds of places where these bees are nesting, that one species might just get there first to occupy them and the other ones can't use them.

[00:27:12] Kate LeCroy: [00:27:12] Yeah. So if we were to think that competition between Osmia taurus and native species was the reason for the decline we observed. Then we really want to look at what are the similarities, how do they share floral resources? Do they use similar nesting resources, for instance? Osmia lignaria, our native Osmia lignaria is the most closely related to Osmia taurus and Osmia cornifrons. And, it uses similarly sized nesting cavities as the exotic species. And this native bee, Osmia lignaria uses the same nesting partition material, mud while the [00:28:00] other native species use chewed leaves. And, it also is one of only two native mason bee species that will emerge as early as the exotic Osmia conrnifrons and taurus in our region.

[00:28:13] Andony Melathopoulos: [00:28:13] So one way you could get at that question of like limiting nest resources is kind of like start to drill down and ask questions about, well, did this species have a similar niche to the exotic species? Because there you'd expect the impact to be most severe.

[00:28:31] Kate LeCroy: [00:28:31] Yes. We would think that Osmia lignaria would have like the greatest potential among native species to really be impacted, but that's not really what we see in our results. We can't see any significant differences between how "bad" all the native species are declining. They're all really bad, but there may be something else other than competition for food and nest resources that's driving this pattern we're seeing.

[00:29:00] [00:28:59] So another possible mechanism could be that diseases from exotic mason bee species are spreading to native mason bee species. So usually when a bee species or any species is introduced, they're probably not coming by themselves so they can have other associates that spread with them. And one of the main diseases really affecting the bee genus Osmia worldwide is chalkbrood and that's, a group of fungi in the genus Ascosphaera.

[00:29:40] Several species of Ascosphaera are native to North America. But there were some researchers in Ithaca, New York in Bryan Danforth's lab that found exotic Osmia cornifrons was harboring a Japanese species of this fungi. [00:30:00] So one thing we're worried about in Virginia is perhaps these Japanese fungi are in our native mason bees now.

[00:30:16] Andony Melathopoulos: [00:30:16] So the cornifrons probably has some kind of resistance to it. It isn't as impacted when this disease spreads out. And so the other, the native species don't have it and they potentially may have a competitive advantage because of the pathogen.

[00:30:33] Kate LeCroy: [00:30:33] That's a really interesting hypothesis, we think. However, there's still a lot to be explored there because some fungi in this Ascosphaera genus can be, more saprophytic and not pathogenic. So it could be that...

[00:30:51] Andony Melathopoulos: [00:30:51] Saprophytic, it's just killing already dead larva?

[00:30:56] Kate LeCroy: [00:30:56] Saprophytic means it [00:31:00] simply enjoys, consuming resources from pollen in the nest or fecal matter in the nest or other things.

[00:31:08] Andony Melathopoulos: [00:31:08] So it's not causing damage,

[00:31:10] Kate LeCroy: [00:31:10] Right, yeah. And if it is, it's merely incidental, but we don't know. So we really want to explore that and I've been working on that. And I'm excited to write that paper about exotic Ascosphaera and native mason bees in Virginia.

[00:31:28] Andony Melathopoulos: [00:31:28] Okay. So we've got competition for resources, both nesting and floral resources. And we've got, potential of a new pathogen coming in. Is there any other, aspects that might be explaining these trends?

[00:31:42] Kate LeCroy: [00:31:42] Yes. I also am curious - I think one reason Osmia cornifrons might have been selected for import into the US instead of Osmia taurus was perhaps Osmia taurus experienced really high levels [00:32:00] of natural enemy attack in Japan. However, if Osmia taurus was able to escape that enemy attack from its native range, and it has reduced pressure from enemies in West Virginia. Then it may have really high, reproductive output. It may be able to really ramp up its productivity in this new environment, where there are fewer natural enemies for it .

[00:32:29] Andony Melathopoulos: [00:32:29] You know, it's fascinating. It reminds me of a conversation I had with Jim Cane once about alkali bees and he mentioned the reason why alkali bees can be propagated in such high numbers is because it may be the only ground nesting bees system that you could do that with is because it really doesn't have any predators. And so the same thing may be happening here. Where a species is sort of released into an environment and it really couldn't do well, but as soon as it's escaped its predators, it really explodes in number.

[00:33:01] [00:33:00] Kate LeCroy: [00:33:01] Yeah. That's another hypothesis we want to explore.

[00:33:05] Andony Melathopoulos: [00:33:05] Wow. What? Oh yeah, you got more?

[00:33:08] Kate LeCroy: [00:33:08] Oh gosh. Yeah! I've been spitballing ideas all during the pandemic of how this pattern could happen. So one more is, perhaps cornifrons and taurus have different climate preferences. And in fact, Osmia taurus seems to be doing really well in warmer climates and it seems to be able to tolerate a wider variety of climate conditions than Osmia cornifrons. So we think that if it's able to do this, then it may be poised to spread much farther in its, introduced range, particularly in warmer areas than Osmium cornifrons ever has been able to. But we still need to explore range expansions, and shrinkages in our native and [00:34:00] exotic Osmia species.

[00:34:01] Andony Melathopoulos: [00:34:01] This is great. I really liked the way you set this all up, because just coming back to your beginning with winners and losers and the mechanisms underlying them, these patterns can be visible and it may be really easy to say, " oh it's just a non-native bee". And, "it's just a bully or something", but actually the nuance of it may help figure out how you can do something about it.

[00:34:26] And I guess that brings me to my last question. Now once you're in a situation like this, when you do have exotic bees that are loose, we have several situations like this across the United States. But in particular with mason bees, where there is a trade of mason bees, what can be done if anything, how can we deal with the situation now that it has occurred?

[00:34:48] Kate LeCroy: [00:34:48] Yeah, thank you for asking Andony. I think there is something that can be done. Companies that sell exotic Osmia cornifrons to farmers or to gardens, or to folks who want [00:35:00] mason bees in their backyard. These companies should really check that they're not accidentally shipping around the nearly identical looking fast proliferating invasive Osmia taurus.

[00:35:12] Those species look basically similar to the naked eye and it's best to tell them apart using a microscope. So if companies are going to sell these bees in the first place then they need to make sure they're not spreading those invasive species. And, I think there should be stronger government restrictions or regulations on importing bees. And it's important, I think, to continue promoting wild bee monitoring schemes so we can track exotic and native bee species distributions and changes.

[00:35:50] Andony Melathopoulos: [00:35:50] Okay, those are great suggestions. So just to recount them. So the cornifrons is out in a number of places and it's not [00:36:00] everywhere. Osmia taurus is the one that we really, really want to be careful of. And I think producers need to, make sure that it's out of their stocks and have a way to weed it out. I also like what you said about, part of that system of being able to know where those bees are and aren't kind of requires some kind of surveillance. Without the surveillance, you'll never know, and it won't give the producers any idea of whether, the cat's out of the bag or not.

[00:36:26] Kate LeCroy: [00:36:26] Right, exactly.

[00:36:28] Andony Melathopoulos: [00:36:28] Fantastic. All right. Well, let's take a quick break. We have a series of questions we ask all our guests. I'm so curious what your answers are going to be. So let's take a break and we'll be right back. Okay. So, we ask all our guests these questions. First question is, do you have a pollinator book recommendation that you want people to know about?

[00:36:50] Kate LeCroy: [00:36:50] Yes, Andony, I do. So, I found this gem of a book that, is free to access online, called "Trap Nesting Wasps and [00:37:00] Bees", and it has all their life history, photos and plates of nest structures. It's by Karl Vorse Krombein and it was published in the sixties. And if you download the whole PDF, it's like five gigabytes, but it's got really great photos. I feel like I learned so much every time I pull it up.

[00:37:27] Andony Melathopoulos: [00:37:27] I've never heard of this book, although I've heard the last name because of the mite. That's the mite guy. Okay. So, tell us a little bit about it, it's interesting it's not called cavity nesting bees and wasps, it's "trap nesting". So this is based on sort of observations that you can make, tell us a little bit more about the book.

[00:37:48] Kate LeCroy: [00:37:48] Yeah. So, this book really documents some year to year what Karl Vorse Krombein caught in his trap nest, often [00:38:00] around Plummers Island, near Washington, DC. And it's a lot of year to year variations. He takes, a beautifully detailed approach to documenting all of the enemies inside the nests, all of the types of bees and wasps that he found. Like what days did they come out? If there was any, what I love is nest succession where one mason bee might start making an nest, but another mason bee female takes over the nest and it's of a different species. So he has these beautiful details of natural history about all of this stuff. Nesting behaviors as well.

[00:38:41] Andony Melathopoulos: [00:38:41] We had a previous episode with, Ron Spendal. Who's a Master Gardener in Washington County and he has a plexiglass tops and he does a lot of very detailed observations. And I wonder, if he doesn't know about this book -  he'll be so excited. Once we're done, I'm sending this directly to Ron.

[00:39:00] [00:39:00] Kate LeCroy: [00:39:00] Oh, great! That work sounds right up my alley. I've made some plexiglass nests as well, they're really awesome.

[00:39:07] Andony Melathopoulos: [00:39:07] Well, the next question I have for you is, do you have a go-to tool for working with pollinators?

[00:39:13] Kate LeCroy: [00:39:13] Yes. So the best tool I know, that gets me through assembling thousands of nesting boxes or even identifying bees is a good Dolly Parton playlist.  It really gets me through, I'll share the public playlist. I made it public so anybody can, you know, start identifying bees or, you know, gardening or observing mason bees. And I recommend playing it on repeat, it's about an hour and a half, but it flows really well.

[00:39:49]Andony Melathopoulos: [00:39:49] We are going to have a link to the Dolly Parton mason bee, block observation, Spotify playlist. This is the first time we've gotten a recommendation like that. I'm really loving this interview. Really [00:40:00] great job Kate.

[00:40:03] Kate LeCroy: [00:40:03] You're welcome.

[00:40:05] Andony Melathopoulos: [00:40:05] Okay, great. Well, you're doing the unusual here. I don't think anybody's done anything like that. Expectations are high for number three, your favorite pollinator species, take it away.

[00:40:18] Kate LeCroy: [00:40:18] Yeah. So,my favorite pollinator species is, guess what? A mason bee. And it's Osmia texana. Osmia texana has really interesting distribution all over north America. And, I went hunting with an undergraduate student named Dawson Little, we went hunting for the species in West Virginia one summer. Because it was rarely occurring at our field station, but we really wanted to go find it and we were able to trap nest it and we found it a lot on thistles. And, we were able to make a pilgrimage to Sam Droege's lab to take photos of this [00:41:00] one particular specimen that had a lot of thistle pollen and gummed up nectar on his body.

[00:41:07] Andony Melathopoulos: [00:41:07] The image that you've sent is this your image?

[00:41:11] Kate LeCroy: [00:41:11] Yes! Sam Droege took that photo.

[00:41:14] Andony Melathopoulos: [00:41:14] Great. And I can see the thistle pollen right there on the scopa.

[00:41:18] Kate LeCroy: [00:41:18] And it's really beautiful.

[00:41:20] Andony Melathopoulos: [00:41:20] It looks like a little critter.

[00:41:24] Kate LeCroy: [00:41:24] Yeah. Osmia texana is about the same, a little smaller than Osmia lignaria but let's say somewhere around eight to nine millimeters long. So maybe the size of your pinky

[00:41:41] Andony Melathopoulos: [00:41:41] It's a beautiful bee, we'll share the image, on the link there. And, you did great on these last questions. It was a great interview. Thanks so much for sharing, information on your research. We're really looking forward to hearing more about it.

[00:41:54] Kate LeCroy: [00:41:54] Thank you so much for your time and for inviting me. I really appreciate it.


Stem nesting bees like mason bees are particularly amenable to being introduced to distant lands. In this episode we hear about research looking into the impact of these introductions on native bee populations.

Kate LeCroy is a PhD Candidate at the University of Virginia studying mason bees (genus Osmia) with T'ai Roulston. Over the last three years, Kate has partnered closely with 200+ citizen science program participants to monitor mason bee diversity and disease ecology across the Commonwealth of Virginia. Along with running training webinars and coordinating the 12-week monitoring projects each year, Kate identifies the springtime mason bees and fungal associates from each location and shares these data back with each participant. Pre-pandemic, Kate would spend a lot of her time each spring driving around the nooks and crannies of Virginia blasting Dolly Parton, visiting her program participants to deliver monitoring equipment and answering any of their questions in person. Kate loves community-building while doing science, and she hopes to do this throughout her career.

Links Mentioned:

Book recommendation:


Dolly Parton Spotify playlist

Favorite Pollinator:

Osmia texana (additional photos)

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