Pollination Services in Cucurbits

- This next session, this afternoon session we're gonna focus in on pollination services and start with cucurbits.

I believe it's one of the simplest ones.

Simplest in the sense that I can focus in on relatively few populations.

There's a lot of diversity that I'll touch on, and yet, I can focus in on populations, which is where I'm most comfortable at, actually.

Focus in on who's doing the job, what species, and talk about farming practices.

I'll start with pumpkin.

It's kind of the simplest system of cucurbits that I'm dealing with.

Among the most pollinator-dependent world wide.

Monecious, separate male and female flowers.

Abundant nectar and possibly toxic or harmful pollen rewards for most of the species.

We've collected data in this Project ICP where we got data for three years, 24 fields, wholesale-marketing fields.

Wholesale marketing, we're talking about relatively large fields, five to 100 acres, where they're trying to get the entire crop harvested in a relatively short period of time.

Earlier than, say, a U-Pick operation or something aiming at farm stands.

And they're fields that are rotated.

People always rotate cucurbits.

Typically three year rotations here.

We made collections of specimens, visitation measures with thousands of transects.

If you look at who is visiting those flowers, we got 37 species.

So, yes, these pumpkin flowers are providing resources for an incredible, diverse array of species of bees.

The community composition was 37 species, but how many visits occurred for each species?

97% of the visits were from three species during July 14th to August 20th.

Relatively short time frame.

And during that relatively short time frame, honey bees, squash bees, that's Eucera, Peponapis and bumble bees.

Seven species of bumble bees, but 98% of 'em was one species, the common eastern bumble bee.

So now I can start focusing in on this population level when I'm thinking about pollination services.

The other species are also possibly involved with pollination, but these species are doing the majority of the work.

The pollen's very big and heavy relative to other pollen, so that's another reason why you need your larger body bees.

Are these wild bees, wild population, sufficient and reliable?

Well, if a pumpkin flower is open for about four hours, that's a typical scenario, opens in the morning, closes when it gets hot, what's the minimum number of visits to a female flower?

Well, it depends on how much pollen they're depositing.

This is the worst-case scenario.

Could well be less than this, but 16 visits by a honey bee, eight visits by a bumble bee over the four-hour time frame.

The bumble bees carry more pollen.

16 with the squash bee, it's about the same size as honey bee.

Here's visitations rates that we measured in that setting.

With our metrics, this would be the threshold you'd have to exceed.

That many visits per 45 seconds, per transect.

This is what we achieved.

So if we were above that line, we got the job done.

Honey bees alone got the job done tenfold.

Bumble bees alone, twelvefold.

Squash bees alone, twofold.

Wild bees, just the wild populations, were providing 14 times the amount of pollen deposition necessary to achieve the kinds of yields that we want.

So wild bees in Pennsylvania are kind of doing the job for pumpkin.

For squash bees, if you see individual visits, you kind of get a rough idea of what the population might be.

But for bumble bees, that may not be true at all.

For example, if we went out into a field and we're counting visits and we saw 200 bumble bees, is that 200 bumble bees from one colony or is that 200 bumble bees from 200 colonies?

The colonies are the reproductive unit, we gotta count the number of colonies to get a sense of what kind of resilience we're dealing with here with these populations.

So we wanted to count colonies.

Keep in mind that bumble bees, at this time of year, we're talking about mid-July to mid-August, by that time, we're dealing with a queen that's in her nest laying eggs.

All her offspring are her daughters.

All the foragers are sisters from a single colony.

We collected 200 foragers per field, roughly, and chopped up their DNA, used this microsatellite markers to sort of figure out essentially paternity analysis.

If you assume that the queen mated once and you just followed how many paternity analysis that you've got, the similar like you might do for humans, then you can estimate the number of colonies.

So the way you do this is you genotype 'em with these microsatellites, so the different colors represent different microsatellite paternities, basically.

You group 'em together and that tells you how many colonies you measured.

So, you know, colony number four, we actually picked up three individuals from colony four, et cetera.

And then you assume that comes from a distribution and you basically use mark-recapture analysis.

We throw 'em all into software, randomly make a poll.

The DNA itself is a mark.

Put 'em all in there, randomly do it again, pull out again.

How many times did you recapture from the same colony?

And with that kind of analysis, you can also estimate the number of unsampled colonies, estimated colony abundance of Bombus impatiens in pumpkin fields.

After you do this work, we average 450 colonies.

That's an average for all 24 fields across three years.

So this is a per-field estimate.

The minimum was 200, the maximum was 760.

And that's the conservative estimate.

There's a couple ways to approach this and we got a lot of bumble bee colonies floating around in this kind of environment.

And they're sending in some foragers and other foragers are going elsewhere, but that's a tremendous amount.

If we looked at the visitation rate, visits per flower per 45 seconds for these bumble bees and we looked at how many colonies we got per hectare, you can see the relationship.

So yes, it's the pollination service, ecosystem service of pollination is a function of the stocking rate, if you will, of bumble bees.

It's not like they, as time went on, we got more colonies, it's essentially pulling in what's in the surrounding landscape.

So at the population level, bumble bee colonies of Bombus impatiens is doing great in that setting.

I talked about squash bees briefly and I wanted to stress that when I go to other kinds of marketing systems, let's say farm stands that have a U-Pick operation, they're trying to get many more cultivars of pumpkins over a much longer period of time.

And also, they're all doing it within their farm, their 20 acres or 50 acres or 200 acres.

And so those fields are close by.

They're rotated, but they're all within that same farmscape.

And in those settings, tremendous numbers of squash bees.

Peponapis, I still call it Peponapis, but it's Eucera pruinosa.

When you go to California, which is another big pumpkin producing area, they don't have the bumble bees in their setting.

So we've got this big bumble bee thing, we've got this squash bee thing.

It's being influenced by the proximity of last year's fields, the timing of your sampling.

We were probably biased 'cause we had a lot of fields to go to, so we got going by a little before seven in the morning and we'd have to finish by the time the flowers closed.

That biases us more towards the bumble bees.

The squash bees, some of 'em would have come and gone by then.

The bee populations are remarkably high in pumpkin in Pennsylvania.

This slide, this is coming from Project ICP from multiple types of crops, from multiple locations.

And you look at the visitation rate from wild bees and you extrapolate how much pollen they were measuring.

So what was the fraction of the total pollen grains that were deposited by wild populations of bees?

We're not dealing with commercial bumble bee things.

And here's pumpkin in Pennsylvania.

We rock.

We totally pushed it on the high end of everything.

It's really a good positive story going on right now.

That's pumpkin.

But when you think about the family Cucurbitaceae, pumpkin and squash is kind of the simplest.

They're totally separate male and female flowers.

You get into these others, you've got male and female, you've got male and perfect, which is male and female in the same flower over here and some that are just male.

You've got a lot of cultivars now with watermelon that are gynoecious.

Most of the plants are almost all female and you have to have a pollenizer row slipped in every once in a while.

You know, melon, you've got male and perfect.

Cucumber, all kinds of things and parthenocarpic coming in.

And I'm sure it's changing.

If you go into greenhouse cucumbers in the parthenocarpic cultivars, you try and keep the bees out.

Because you don't want any seeds setting by accident.

So it gets a lot more complicated if you start thinking about the entire Cucurbitaceae.

This is something from the literature where, in this case, it was Midwestern locations.

28 species visiting cucumber.

Honey bee was greater in eight of the 10 farms.

Wild bees greater in two of the 10 farms.

I generally see more reliance on honey bees as I go into cucumber.

Again, a large range of species.

And another big thing that's important here, is these flowers, now, are open pretty much all day and they're much smaller.

That's gonna affect pollinator safety issues.

Watermelon is also much more diverse.

This is Rachael Winfree and Neal Williams and others.

23 farms in counties that border New Jersey and Pennsylvania.

Here's the visits by wild bees, the visits by honey bees.

If it was equal, it'd be on this 45 degree line.

So you can see wild bees were prevalent in 16 of the farms.

Honey bees were prevalent in seven of the farms.

So as we move into all the different cucurbits and all the different cultivars, it's gonna jump around quite a bit.

I started with pumpkins, 'cause it's the easiest.

So who visits?

You've got this honey bee, bumble bee, in this case, squash bee for the pumpkin and squash and a wide array of other species and the relative importance is gonna jump around.

In some respects, for some of these, for the pumpkin and squash, I think the crop is actually providing a resource for the wide array of species that are in the landscape.

But I wanted to back up a little bit and say we've got something good going on.

Why?

And what do we need to conserve it?

We've got a landscape, now, that is providing an ecosystem service, certainly to the pumpkin, squash group and also spilling out to the other cucurbits.

It is safe?

What about our farming practices that are useful for this, helpful for this and what are harmful?

It can change quickly.

So, you know, here you are in a pumpkin field.

Believe it or not, this is a flowering pumpkin field.

You let the fog lift and you wait a few hours and you get all these blossoms popping up.

What are some of the things we need to think about?

Is flowering, compared to a lot of the other crops, the dewberries, the tree fruit, in those kinds of settings, you've got a narrow window of flowering.

You might have, for some of these things, you might have two weeks.

Now, across a farm, you might have multiple cultivars, but you've got this distinct flowering time.

And so you can take the stressors or at least the fungicides, insecticides and break away from that.

That's harder to do with the cucurbits.

That you've got this consistent flowering just dragging on and dragging on.

Also, when in the day?

So you've got some opportunities there.

In the case of pumpkins and squash, the flowers close.

So if you do need to put on a spray, wait 'till the flowers close and that helps you a lot.

The plant populations, tremendously different.

Pumpkin, squash, it depends on the size of the pumpkin that you're after.

Spacings that might be 1,000 plants per acre, 1,500, maybe 2,000.

Pickling cucumbers, over 100,000.

That's gonna change the amount of flowers that need to be pollinated.

How many flowers are out there.

It's also gonna be an important component to think about when we talk about neonicotinoids on the seed.

'Cause if you take small amounts of neonicotinoids, which is a big concern, and you put it on pumpkins, well, you're putting it, you know, you've got 1,500 seeds.

You put it on soy beans, you get 200,000 seeds.

So plant populations are real important.

Also, that becomes important in terms of what kind of seed, what kind of set you're after.

The commercial wholesale market, we're setting 1.7 pumpkins per plant.

That's it.

The rest of them are gonna abort, things like that.

So your pollination needs get influenced by that a lot.

Is the plant providing nutrition for the bee?

Nectar, yeah.

Pollen, for the squash bee, yeah, but maybe not for the others.

And that's gonna differ a lot as we talk about different crops.

Let me return a little bit to nesting and tillage.

Rotation's real important for, you know, we rotate cucurbits on three-year basis at least.

If we deal with rotation, the specialists that are necessary, which include the squash bee, they've gotta have cucurbits in the system every year or else you're gonna wipe 'em out.

The squash bees, they visit more quickly than the honey bees.

They're more reliable.

They disperse pollen over greater distances.

The adults emerge July 4th was what I thought of as the first.

I think it's shifting a little earlier.

They go through about two to three weeks of pre-nesting, maybe dispersal behaviors.

So they're overwintering as, I believe, an adult or prepupae.

And they're coming out kind of late.

So if you've got your cucurbits out before this, you're not taking advantage of it.

And the females make these nests five to nine inches deep, four to five cells per nest.

And maybe they'll make several nests.

They're the only group, in insects that I deal with, that are central place foragers.

They build their nest and they forage out from that one location.

What are we dealing with?

20, 30, 50 maybe at most, offspring.

I don't have any pests that are that frugal.

The lowest I go is 200.

It's common for me to think about 500 to 1,000.

I've got some species that'll give me 3,000 eggs per female.

Jim helped me out once when we were walking around trying to imagine this.

And he's listening to me, said, "Well, stop thinking about that.

"Think about little small mammals." And so there are fewer of them.

So they're a little more precious.

The larvae feed on the pollen, overwinter as prepupae.

So this is about, this is a picture of a nest.

Little antechamber that might be important for humidity and other microenvironmental controls.

They make their nest and they provision the nest to close it up with an egg in there and they seal it.

So that nest, that might be built in late July, early August, that little cell has to sit in the soil and come out the next year, in July.

During that whole time, if you disturb it, you know, will it survive?

And that's where we get into questions of tillage.

They lay their nests right in amongst the vines or right close by in, you know, edges of fields.

This was what happened in a plasticulture system where you're familiar with the raised beds, plastic mulch, drip irrigation.

And so Ric Bessin and his colleagues, they created these kind of tunnels and they threw in females and they did it repeatedly.

And over a course of a season, you accumulate an idea of where their nesting.

So in a plasticulture system, there's your plastic row bed here.

These are the alleys on either side.

These are the cucurbit plants, the green.

So you can see right around the holes where the weeds come up, they were crawling in there and nesting around there, but overwhelmingly, they were getting their stuff in the soil nearby.

Tilled soil that they could nest in.

Here's what happened in a strip tillage system where you had a no-till zone on either side and the thatch was pretty thick, but you tilled a narrow strip, you know, maybe about yea wide, put your cucurbits in there and then they nested in the tilled zone.

So that's where you'd wanna preserve them.

In farms that had no-till in their farmscape, this is over studies in Maryland, Virginia from Schuler, Roulston.

No-till farms had three times the amount of squash bee visitation rates.

When it comes to cover cropping and no-tillage, Pennsylvania ranks among the top.

The whole Northeast ranks among the top.

And we're also getting a lot of no-till adoption happening in pumpkins.

So here's the bumble bee life cycle.

I wanted to stress two points of that life cycle.

This overwintering queen has to get out there in the spring, do all her work to get the first brood going.

That includes making a honey pot, a wax pot, filling it with nectar, it takes a lot of energy.

She's gotta do it all by herself.

Towards the end of the year, she's gotta have the resources to get all through the winter.

These two points are critical points of the life cycle.

And so provisioning resources to those points for the common eastern bumble bee is what we try to do.

We did targeted floral provisioning for this kind of thing, where we created a cover cropping system of fall-planted crops, where you gonna put your crop next year, that would flower in the spring to help provide food for this queen as she overwintered.

And then a summer-planted crop right after that we put in this mix and get a bunch of resources out there for that late season.

We achieved it with this kind of scenario.

Cover cropping mixes.

There hasn't been nearly as much breeding of cover crops as there are of other crops, but that's a emerging area that deserves a lot more work.

We gotta deal with pests.

This one, this one and this one all transmit pathogens, so we've got to deal with pathogens.

Systemics are typically used.

The neonics came in in the mid and late-90s.

And what I was focusing on was the improvement for farm worker safety, 'cause these are all, I'm working primarily in small farms with a lot of hand labor.

So this is what I was replacing that takes, you can see like a 30 to 50-fold improvement on what it takes to hurt a human.

So that is great.

Transgenic options work to stop diseases.

We have 'em in squash.

If we could stop diseases with whole plant resistance, that would have a tremendous impact.

And real quickly, the residues, we can return to this with the stressors, but if you do use neonic seed treatments which are common now, residues are higher in pollen than in nectar.

The amount that shows up is influenced a lot by how the plant grows.

Seed treatment had the lowest residue.

Here, imidacloprid applied to the transplant before putting out there, you can see, 0.1 part per billion versus 31.

Thiamethoxam, which is Cruiser, 0.1, compared to transplant-drip, which was 24.

So if we could just say, "Use it on the seed treatment "and not at all afterwards," which I do think is feasible, you're down at this 0.1, and by the way, this was a study were the limit of detection was 0.2, so it was basically below their limit of detection.

Most of the sprays in pumpkins go for fungicides and we are kind of early on our understanding of how fungicides interact with bees and synergize with insecticides.