Bees and army bands: The remarkable life of TB Mitchell

This is a guest post from our Research Associate, Elsa Youngsteadt

T. Mitchell

A portrait of T.B. Mitchell in the lab. Image courtesy of Special Collections Research Center, North Carolina State University Libraries; photographer unknown.

T.B. Mitchell is probably the reason we ecologists in eastern North America can identify our bees. Mitchell joined the faculty here at NC State in 1925 and distinguished himself as a meticulous taxonomist.

Although he died in 1983, more than 30,000 of his bee specimens are housed here in the NC State Insect Museum, where one can occasionally feel a little time warp: The specimen I am examining right now, under the microscope, was alive in 1925. It was cruising from flower to flower along some North Carolina country roadside 91 years ago when Mitchell nabbed it with his net. He pinned it, identified it, labeled it, may have studied it while writing the key I’m now using—and I’m handling that exact bee, comparing it to one of the same species that I caught last week.

Enough of this kind of thing, and you wish you could meet the guy who made the collection. Thanks to lab alum April Hamblin’s idea to propose a Heritage column for American Entomologist, we nearly feel that we have. April, Margarita López-Uribe, Heather Moylett, and I spent the better part of a year, off and on, going through boxes of letters and stacks of theses, reading Mitchell’s papers, and conducting interviews and correspondence—including actual paper letters. The resulting article is published in the fall 2016 American Entomologist. We invite you to read it and get acquainted with this energetic, unflappable gentleman, his scientific contributions, and his remarkable experiences as a musician and entomologist.

August 30th, 2016|Categories: Lab Happenings, Natural History and Scientific Adventures, Pollinators|Tags: |

Squash Bees Are Pollinating Your Pumpkins and Zucchini

This is a guest post by Research Associate Elsa Youngsteadt

For years, I have felt rather sheepish for never having seen a squash bee. As native bees go, these fetching little stripey, round-faced bees get a lot of press. They’re common and easy to recognize, and they happen to do a very specific job that’s easy to appreciate: They pollinate around 2/3 of the commercially grown squash in the US. When bee enthusiasts are polled for their favorite species, someone always picks the squash bee. So yeah, I felt a little left out.

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This female squash bee has been foraging in this male flower (note the pollen on her back legs). (Photo: E. Youngsteadt)

The problem with squash bees (Peponapis pruinosa) is that they get up really early in the morning. They have an unusual relationship with plants in the genus Cucurbita, which includes summer squash, winter squash, zucchini, pumpkins, and many gourds (but not cucumbers). Female squash bees provision their nests exclusively with pollen from Cucurbita flowers and often build their burrows in the soil right under the plants. Even the male bees spend a lot of time at the squash flowers—not just to dine on their plentiful nectar, but also to meet the ladies who come in searching for pollen.

Specializing on squash flowers means waking up at dawn, when those flowers first unfurl. By mid-day, the blossoms crumple, ready to fall off the vine. So by the time I’m out working in the garden, this is usually what I see on a pumpkin vine: Drab remains of flowers, and no bees.

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This is Cheddi. He wants you to get up and look at your squash bees. (Photo: E. Youngsteadt)

It might have gone on like this indefinitely had we not adopted a cat last winter. Meet Cheddi, a lovey-dovey and very verbal Maine Coon who likes mornings nearly as much as squash bees do. This summer, just when my pumpkins were starting to bloom, Cheddi was in full alarm-clock mode at 6 am: Come on, sleepy people, you are wasting time. You’re not up yet? You should be doing things! Get up! You could come and feed me. Are you awake NOW? It’s morning! Things are happening!

Some days, the silent treatment just doesn’t work. Also, the chickens were making a ruckus. So, still pajama-clad, I shambled out into the dewy dawn past the pristine, glowing-orange pumpkin flowers to let the hens out. And groggily wondered—hey, it’s early, and I have squash flowers. Maybe there are bees.

There were. There was a female, head-first in a flower, her back legs fat with yellow pollen. I felt initiated. And in fact, I’ve seen the bees most mornings since. They’re almost always still out by 8 or 9 am, at which point a few other species—hibiscus bees, green sweat bees, two-spotted long-horned bees, and even honey bees—show up in the flowers, too.

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Squash bees are similar in size to honey bees, but have a rounder, more robust build (and forage earlier in the morning). (Photo: E. Youngsteadt)

Female flower_small

Each female squash flower starts out with a tiny fruit behind it, but the fruit will only develop if the flower is pollinated. It takes 6 – 10 squash-bee visits to fully pollinate a flower. (Photo: E. Youngsteadt)


From the plant’s point of view (and the gardener’s), these insect visitors are indispensable. Cucurbita’smale and female reproductive parts are housed in separate flowers, and their pollen grains are big and heavy. Bees (or, ok, hand pollination) are the only means to get them from one flower to another. It is no exaggeration to say that without bees, there would be no squash. Not just smaller, uglier ones; none at all.

It takes only 6 to 10 squash-bee visits to fully pollinate a female flower—and squash bees normally get this much done in the first half-hour of foraging. At that point, it’s still barely even full daylight out, and other bees are barely beginning to forage. Although honey bees and bumble bees can also be decent to excellent pollinators for squash, they are superfluous in the presence of the early-rising squash bees.

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It works: I have pumpkins. (Photo: E. Youngsteadt)

If you want to encourage these bees in your own garden, there are a few things you should know about them. They are pretty common in suburban areas to begin with—more so than in natural areas, since our cultivated squash are more common than wild gourds in most parts of the country. I only have two pumpkin vines, and the next-door neighbor grows some zucchini, and that seems to be enough to attract the bees.

Because they nest in the ground, often right under the squash plants, these bees are sensitive to things you may do to your garden soil. The female bees usually build their nest cells 6 to 12 inches underground, and the next generation of bees spends most of the year helplessly sealed inside those cells. So tilling a squash bed at any time of year can destroy a lot of bees. A census of 25 squash and pumpkin farms in Virginia found three times more squash bees on no-till farms than on those that tilled.

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Male squash bees may crowd into a flower together, drinking nectar and waiting for female bees. (Photo: A. Nagle)

Other soil treatments may matter, too. One study showed that the bees tend to be more common on irrigated farms. And another found that they seem willing to dig through a modest, 2-inch layer of mulch to make their nests—although these researchers had some trouble with their bees and only had four nests to go on.

Finally, be aware of pesticides in the garden. Squash plants get some pests—such as cucumber beetles and squash vine borers—that may require your intervention. But never apply an insecticide to a flowering squash plant, and bear in mind that systemic insecticides applied before flowering can still turn up at toxic levels in squash pollen. The immature bees in underground nest cells will be exposed to chemicals applied to the soil at any time of year, although no research has yet found a link between pesticide use and squash bee abundance on commercial farms.

Even if you’re not up early enough to see them, or even if you’ve had your harvest and torn out your squash vines—remember that these little bees are there year round, much of it spent underground waiting for the next season of squash flowers.

Sources and further reading

Video about the squash bee life cycle

Slide show from the USDA about squash bees as pollinators

Artz, DR, and BA Nault. 2011. Performance of Apis mellifera, Bombus impatiens, and Peponapis pruinosa (Hymenoptera: Apidae) as pollinators of pumpkin. Journal of Economic Entomology 104:1153-1161.

Cane, JH, BJ Sampson, and SA Miller. 2011. Pollination value of male bees: the specialist bee Peponapis pruinosa (Apidae) at summer squash (Cucurbita pepo). Environmental Entomology 40:614-620.

Dively, GP, and A Kamel. 2012. Insecticide residues in pollen and nectar of a cucurbit crop and their potential exposure to pollinators. Journal of Agricultural and Food Chemistry, 60:4449-4456.

Hinners SJ, CA Kearns, and CA Wessman. 2012. Roles of scale, matrix, and native habitat in supporting a diverse suburban pollinator assemblage. Ecological Applications 22:1923-1935.

Julier, HE, and TH Roulston. 2009. Wild bee abundance and pollination service in cultivated pumpkins: farm management, nesting behavior and landscape effects. Journal of Economic Entomology 102:563-573.

Mathewson, JA. 1968. Nest construction and life history of the eastern cucurbit bee, Peponapis pruinosa (Hymenoptera: Apoidea). Journal of the Kansas Entomological Society 41:255-261.

Shuler, RE, TH Roulston, and GE Farris. 2005. Farming practices influence wild pollinator populations on squash and pumpkin. Journal of Economic Entomology 98:790-795.

Splawski, CE, et al. 2014. Mulch effects on floral resources and fruit production of squash, and on pollination and nesting by squash bees. HortTechnology 24:535-545.

Stoner KA, and BD Eitzer. 2012. Movement of soil-applied imidacloprid and thiamethoxam into nectar and pollen of squash (Cucurbita pepo). PLoS ONE 7:e39114.

Tepedino, VJ. 1981. The pollination efficiency of the squash bee (Peponapis pruinosa) and the honey bee (Apis mellifera) on summer squash (Cucurbita pepo). Journal of the Kansas Entomological Society 54:359-377.

August 17th, 2015|Categories: Natural History and Scientific Adventures, Pollinators|Tags: |

Happy moths, very sad squash

This is a guest post by Annemarie Nagle

I planted yellow crookneck squash this year as an afterthought, after coming across a half-full packet of seeds and pushing last year’s disappointing crop out of mind in a hopeful bout of springtime enthusiasm.

wilty_squash_smallBy June those babies had grown big, lush and beautiful, and friends stopping by remarked on how great the garden was looking. A couple of weeks later and now those giant squash plants are looking more like an embodiment of how I feel after working in the NC heat for a few hours: pretty wilty.

The nemesis at work in my garden is an insect that will be familiar to aspiring squash (and zucchini and pumpkin) growers from Canada to Argentina. Melittia cucurbitae, the squash vine borer, and its host plants in the genus Cucurbita are native to North and South America. In fact, along with maize and beans, squash were cultivated by the Native Americans as one of the ‘Three Sisters’ that provided the agricultural staples for many tribes.

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Wet, brownish frass volcanoes coming out of your squash vines are a sure sign there are borers inside. Photo: A.M. Nagle

M. cucurbitae adults are beautiful orange and black clearwing moths. They fly during the day (most moths are active at night) and are often mistaken for wasps when encountered in the garden. They lay their eggs along the base, stems, and leaves of squash plants, and the larvae burrow into the stem immediately upon hatching. They set up shop and feed for several weeks through the center of the stem, eventually cutting off water flow to the rest of the plant: thus, the wilting.

The fact that I grew yellow squash in my garden last year (and lost them to borers) didn’t do this year’s plants any favors either. The mature caterpillars, which at this point in the year look like chunky, inch-long grubs with amber heads, chew their way out of the stem and drop into the soil, where they will bury themselves a few inches deep and pupate. There are two generations per year in NC, so the first generation will re-emerge as adults in a few weeks to polish off whatever plants they didn’t get the first time (or any new ones you’ve been hopeful enough to plant). The second generation will overwinter in the soil as larvae or pupae encased in cocoons and will emerge come spring.

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Part of the vine removed to reveal the nearly full-grown caterpillar within. Photo: A.M. Nagle

If you are a more dedicated gardener than I am (I’m a plant pathologist, and better at killing plants than keeping them alive…), there are several measures you can take to protect your squash plants from borers. Lightly tilling the soil in late winter can expose the overwintering pupae to the elements. Also, be sure to destroy squash plants when they are done producing to prevent any borers inside from developing, and rotate locations or years for growing squash. For vining varieties such as pumpkins, which can grow new roots at each node, burying portions of the stem encourages the growth of extra roots that can help portions of the plant survive, even when other portions are eventually attacked.

Keep an eye on your squash for the first signs of borer attack: the presence of eggs, then pin holes and brownish, wet frass accumulating at the base. You can ‘deworm’ your vines by making lengthwise slits in the vine near these holes and killing the larvae inside with a knife or pin. Pile an inch or so of soil or compost around the cut to prevent the vine from drying out and encourage rooting.

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M. cucurbitae adult hanging around my cucumber vines. Photo: A.M. Nagle

Insecticide treatments can prevent hatching caterpillars from burrowing into the stem, but are ineffective if you miss this window, so careful monitoring of adult moth activity is important. Adults are attracted to yellow (think squash flowers) and you can monitor when they become active in your garden by placing out a yellow bowl filled with soapy water in late May. Also bear in mind that squash depend on beneficial insects—bees—for pollination, so insecticides should not be applied to flowering plants.

There are some Cucurbita varieties that seem to be less preferred by the borers, particularly those derived from C. moschata, including butternut squash and some types of pumpkin. I’m thinking perhaps a packet of butternut seeds should be waiting for me next year when planting fever hits.

August 12th, 2015|Categories: Landscape IPM, Natural History and Scientific Adventures|Tags: , , |

Cicada Killer Wasps Are on the Wing

This is a guest post by our Research Associate Elsa Youngsteadt

A male cicada killer perches atop a retaining wall, keeping watch over his territory. (Photo: E. Youngsteadt)

A male cicada killer perches atop a retaining wall, keeping watch over his territory. (Photo: E. Youngsteadt)

North Carolina’s steamy July days bring out some of our most spectacular solitary wasps. These sleek and streamlined hunters are quite docile toward humans, but are to be feared by other insects and spiders. The largest of these wasps in North Carolina is the cicada killer (Sphecius speciosus). Females can be up to an inch and a half long and weigh about a gram—as much as a shelled almond.

Cicada killers are solitary, meaning that each female typically builds her own nest and hunts prey to feed her own offspring. (In this habit, they differ from yellowjackets, hornets, and paper wasps, which live in social colonies.) Nevertheless, cicada killers do tend to be found in groups, since they all agree on what makes a good nesting area: sparsely vegetated, southeast-facing slopes or unmortared retaining walls, with plentiful cicadas in nearby deciduous trees.

NC State’s campus hosts a few such cicada-killer neighborhoods, and we started to see the wasps out and about last week. But they haven’t quite gotten around to killing cicadas yet.

Although individual cicada killers have unique markings, they differ from other, similar species in size, body shape, and overall color pattern. (Photo: E. Youngsteadt)

Although individual cicada killers have unique markings, they differ from other, similar species in size, body shape, and overall color pattern. (Photo: E. Youngsteadt)

Males emerge a week or two before females, and spend their time feeding at flowers or sap and establishing territories, where they perch on vegetation or stones to keep watch. They make sorties to chase off other males, pursue females, and investigate intruders—including you, your pet, or your camera lens. Once you know that males cannot sting, these hovering advances (described by one pair of biologists as “businesslike”) can seem quite charming.

This male thoroughly investigated me and my camera before settling down for a photo shoot. (Photo: E. Youngsteadt)

This male thoroughly investigated me and my camera before settling down for a photo shoot. (Photo: E. Youngsteadt)

When the females finally emerge, they mate—only once, but for a long time (30 to 50 minutes). When they settle on a good spot for a nest, the earth-moving begins, and herein lies the occasional conflict between cicada killers and humans. One female wasp can excavate nearly a half-gallon of soil for a single burrow, which can be up to 40 inches long! And she makes about four burrows in her lifetime. She piles the tailings in a neat but largeish U-shaped mound at the entrance of each burrow, and this pileup can damage turf and other plants. But keep reading.

Cicada killers also benefit trees by hunting large insect herbivores—namely, dog-day cicadas in the genus Tibicen. These are the camo-colored, thumb-sized insects that spend their brief adult lives in July and August shrieking and buzzing in the treetops or sawing into branches to lay their eggs.

In her lifetime, one female cicada killer can gather 100 or more cicadas (a hundred!)–each of which weighs about twice as much as she does. She paralyzes the cicada with her stinger and hauls it laboriously back to her nest. She brings one cicada for each of her male offspring, and two or three for each female. (The wasp knows in advance the sex of the next egg she will lay, and stocks the nest accordingly). Then she lays an egg at the base of the cicada’s middle leg and seals up the nest chamber that contains it, never to meet her offspring.

The eggs hatch in a day or two and the long-necked larvae develop quickly, each one polishing off a whole cicada in less than four days. Upon completing its meal, the larva spins a silken cocoon and enters diapause, remaining in a suspended state until the following May or June, when it pupates. That brings us back to the present season, when adult wasps emerge and dig their way out of their nursery tunnels in July—males first.

Entrance to a cicada killer burrow between stones in a retaining wall. (Photo: E. Youngsteadt)

Entrance to a cicada killer burrow between stones in a retaining wall. (Photo: E. Youngsteadt)

If you have cicada killers on your property and find that you really can’t endure them, despite their docile manner and benefits for trees, there are few proven options for control. One study in West Virginia eliminated cicada killer activity on a golf course by spraying the appropriate insecticide directly into active burrows, or immediately around their entrances. (Broader area sprays were not particularly effective.)

However, because the developing larvae may survive this treatment, and because good nesting habitat remains appealing to new females year after year, wasp removal will likely be an annual battle. In most situations, the benefits controlling cicada killers with insecticides are unlikely outweigh the financial and environmental costs.

Other wasp biologists have recommended fertilizing and liming the soil in the affected area to promote thicker vegetation that will eventually deter the wasps; one has informally demonstrated a laborious but effective control method that involves plugging burrows and using a badminton racket to swat the wasps. (Again, this would be an annual undertaking.)

I hope that you don’t have to go to all that trouble, and that you can enjoy watching these insects, instead. And stay tuned for updates on our campus wasps. Once we find females dragging cicadas to their nests, there will be another photo shoot!

Sources and further reading:

Dambach, Charles A., and Eugene E. Good. 1943. Life history and habits of the cicada killer in Ohio. The Ohio Journal of Science, 43: 32 – 41.

Evans, Howard E., and Kevin M. O’Neill. 2009. The Sand Wasps: Natural History and Behavior. Harvard University Press. pp 37 – 43.

Hastings, Jon M., et al. 2010. Size-specific provisioning by cicada killers, Sphecius speciosus, (Hymenoptera: Crabronidae) in North Florida. Florida Entomologist 93: 412 – 421.

Holliday, C. W., and J. R. Coelho. Improved key to new world species of Sphecius (Hymenoptera: Crabronidae). Annals of the Entomological Society of America 99: 793 – 798.

Weaver, Joseph E. 1995. Life history, habits, and control of the cicada killer wasp in West Virginia. West Virginia University Agricultural and Forestry Experiment Station, Circular 161.

There is also a wealth of information, videos, and ideas for controlling cicada killers at the websites of biologists Chuck Holliday and Joel Coelho.

July 20th, 2015|Categories: Feature, Natural History and Scientific Adventures, Urban Ecology|Tags: |

Hoverflies – Bee mimics provide pollination and biocontrol services

Hoverfly on Chrysogonum virginianum. Photo: SD Frank

Hoverfly on Chrysogonum virginianum. Photo: SD Frank

You can often see hoverflies zipping in and out of flowers in your garden. They approach a flowering shrub or group of flowering perennials and hover around seemingly deciding which flower to feed from. A nice part about hoverflies is that they frequently land on flowers to rest providing great photo opportunities for even the clumsiest and least patient phone-wielding gardener or child. Hoverflies are often mistaken for bees. This is called Batesian Mimicry after Henry Walter Bates who studied butterflies (among other things) in the Amazon and first described the phenomenon of harmless species mimicking unrelated harmful species as a form of protection from predators. In this case, many hoverflies, which don’t sting, mimic bee species that do making predators think twice before grabbing them.

The superficial similarity continues since hoverflies also pollinate flowers, though not always as efficiently as bees. Hoverflies visit flowers to feed on nectar or nectar and pollen depending on the species. This gives them the energy and nutrients they need to reproduce.

Reproduction is where hoverflies and bees diverge. (Evolutionarily bees and flies diverged a long time ago during). Most hoverflies have free-living predatory larvae. Hoverfly adults lay eggs on plants near aphid colonies. The maggots move within the aphid colony grabbing aphids with their mouths and eating them. These are very easy to find if you want to see them in (slow) action. Look at milkweed, tulip poplar, any plant with a bunch of aphids. Look closely among the aphids and you will often see green or yellow hoverfly maggots.

Hoverfly larva on a tulip poplar leaf. The tree had many aphids. Notice aphid mummies in the background. Photo: SD Frank

Hoverfly larva on a tulip poplar leaf. The tree had many aphids. Notice aphid mummies in the background. Photo: SD Frank

Hoverflies can be valuable for biological control of aphids in crops like lettuce and grains on which aphids are common pests. Hoverflies can fly far into crop fields to home in on aphid colonies and lay eggs. A lot of research has investigated ways to attract and conserve hoverflies and other aphid predators like lady beetles in crop fields by planting flowers.

Even urban yards can have great hoverfly diversity. As you might expect the best way to attract hoverflies is by planting flowers. But remember flowers are not all they need; they also need aphids for the maggots to develop. Maintaining a “pest free” yard reduces the abundance and diversity of all the predators and parasitoids that rely on those herbivores as food. So when you see a few aphids don’t go nuts. Think of them as food for lady beetles (which also won’t lay eggs without aphids present), hoverflies, minute pirate bugs, bigeyed bugs, lacewings, parasitoid wasps, aphid midges, and hundreds of other insects. Expecting to conserve charismatic insects like hoverflies and lady beetles while eliminating aphids and other herbivores is like trying to conserve lions without gazelles, water buffalo, and zebras.

 

June 4th, 2015|Categories: Natural Enemies, Natural History and Scientific Adventures, Pollinators|Tags: |

Clumsy native bees benefit you and me

This guest blog is by April Hamblin, an M.Sc. student conducting research on urban bees in our lab.

What comes to mind when you think of bees and pollination? Most people immediately think of honey bees and bumble bees, but forget the native bees that inhabit the many natural and urban landscapes around us. In fact, there are more than 500 species of native bees in North Carolina alone.

A great deal of research has shown that these wild bees actually pollinate better than the managed, exotic honey bee. Why is this, you ask? It turns out that the native bees are less efficient than honey bees at holding on to all of the pollen grains they collect, which allows for more efficient pollination as it falls from their bodies. This is great for the plants themselves and anyone that likes to eat plants and their products. Native bees have also been shown to continue foraging in not-so-ideal-bee weather, such as cloudy days, when honey bees like to stay inside their hives.

Apis mellifera

Honey bee (Apis mellifera). Photo: Laura Daly

Melissodes bimaculata

Native bee (Melissodes bimaculata). Photo: Laura Daly

 

On the left is a honey bee (Apis mellifera) and on the right, a native bee (Melissodes bimaculata). The bright yellow dots you see on the bees are pollen. What you may notice is that the honey bee keeps most of its pollen neatly packaged on its hind leg in a specialized pollen carrying basket called the corbicula. In contrast, the wild Melissodes bimiculata uses nearly its entire body to collect pollen. In bee species other than the honey bee, any body part modified to carry pollen is called the scopa.

Here is a good way to think about the difference between these two pollen-carrying systems, and the resulting differences in pollination efficiency. Imagine you were trying to carry four boxes of donuts to your co-workers in the morning. Carrying the boxes neatly stacked in your arms would be the honey bee method. If you were using the native bee method, you’d hold them with your arms and feet, try to balance some on your head and back, maybe even a shoulder–and guess what? You’d drop lots of donuts. It is the same for the native bees that carry pollen in many different places–lots of it falls off as they visit new plants, making them excellent (if slightly clumsy) pollinators.

March 31st, 2015|Categories: Feature, Natural History and Scientific Adventures, Pollinators, Urban Ecology|Tags: |

Boxwood leafminers ready to pop!

Boxwood leafminer larvae are plump and ready to pupate. My daughter and I found a bunch of larvae in bushes in our neighborhood near NC State. These are easy to find. Boxwood leafminers feed within boxwood leaves causing the leaf to become blistered and a little puffy. Take a leaf that looks blistered and tear it open. You will see the bright orange larvae wriggling around inside.

Boxwood leafminer larvae. Photo: IG Frank

Boxwood leafminer larvae. Photo: IG Frank

Last year boxwood leafminer adults emerged on April 15 in Raleigh. At this point, the larvae are not feeding much if at all so systemic insecticides won’t do any good.  You can target the adults with a product that contains abamectin, like Avid.

Acorn top filled with boxwood leafminer larvae. Photo: IG Frank

Acorn top filled with boxwood leafminer larvae. Photo: IG Frank

The larvae do not feed much in the summer, but feed heavily in the fall. Thus, a systemic like imidacloprid applied in late summer will kill the larvae as they feed. Larvae also feed heavily in early spring to complete development, so imidacloprid applied in late winter can also kill larvae. Of course, by this point much of the damage is done, but it will reduce adult emergence.

At the end of our walk my daughter and I ripped open a dozen or so leaves and 8-12 larvae wriggled out of each one. We collected all of these larvae in an acorn top just to see how much we could fill it.

March 26th, 2015|Categories: Landscape IPM, Natural History and Scientific Adventures, Nursery IPM|Tags: , , |

The bees are back in town…digging in the yard

Actually, these Andrenid bees never left town. These small native bees spend most of the year underground and emerge every spring. I have written about their biology before.

Bee emerging from its mound. Photo: S.D. Frank

Bee emerging from its mound. Photo: S.D. Frank

One question I have always had about these bees is: “What do they eat?” Looking around the neighborhood I don’t see many flowers. I have seen the bees loading up on camellia pollen but that is certainly not what they evolved to do. What are these little bees eating in urban and suburban habitats and what plants did they evolve with?

In my yard I have four plants blooming: Crocus, Oregon grape (Mahonia aquifolium), native pachysandra (Pachysandra procumbens), and witch hazel (which is really about finished). Oh, pansies are also blooming.

Mahonia aquifolium

Mahonia aquifolium. Photo: S.D. Frank

Pachysandra procumbens

Pachysandra procumbens. Photo: S.D. Frank

Looking on the ground this is all the bees have. Looking up, though, I see red maples blooming which are an important early season pollen source for native and honey bees. Other trees like red bud are also starting to bloom.

Elsa Youngsteadt, in my lab, is doing some initial work on these bees and what types of pollen they collect and how they use red maples, which are one of the most common street trees. This will compliment some of the other native bee research being done by April Hamblin and Margarita López-Uribe.

March 25th, 2015|Categories: Natural History and Scientific Adventures, Pollinators||

Ants eat your crumbs. What’s the fuss?

This is a post by our Research Associate Elsa Youngsteadt about her new paper in Global Change Biology.

The first time we came back to an empty cage in Highbridge Park, I thought there was a problem.

This was a cage cobbled together out of a fry basket from a restaurant supply store plus a square of hardware cloth, and it was firmly tacked to the ground with landscape staples. With its snug, quarter-inch mesh, it should let most insects move freely, while keeping vertebrates out. With holes any bigger than a quarter-inch, mice could squirm through.

Exclusion cage made from a fry basket to keep food scraps safe from rats. Photo: EK Youngsteadt

Exclusion cage made from a fry basket to keep food scraps safe from rats. Photo: EK Youngsteadt

And they would want to, because the cage held a chunk of Nilla Wafer, a Ruffles Original potato chip, and a slice of Oscar Meyer turkey frank. Yum.

The purpose of the cage was to let us measure how much arthropods* alone were capable of eating in this Manhattan park, without interference from mice, rats, sparrows, and whatever other urban critters might shuffle by with the munchies.

(*Arthropods meaning “bugs,” like sowbugs, mites, millipedes, and insects—including ants.)

So I was dubious when we found an empty cage in Highbridge Park on the first day of our study. Could bugs alone have eaten our little pile of food in a day? When we did a trial run back home on the NC State campus, the food never disappeared completely like that. Had a mouse gotten in after all? Had a human passer-by toyed with our experiment?

So we tried again. We moved our setup to a new spot nearby, tucking it discreetly among the trees and undergrowth behind the ball field. We fortified the cage until it bristled with cable ties and landscape pins. And came back a day later.

This time, our arrival was timely. The cage was surrounded by a silent, busy swarm of pavement ants, trundling off the last fragments of potato chip, the last few cookie crumbs. Ants. Not mice, not tampering humans; ants.

This was a scene we would see over and over in the next several days. And maybe we shouldn’t have been surprised.

Ants feasting on hotdog, chip, and cookie in the cage. Photo: EK Youngsteadt

Ants feasting on hotdog, chip, and cookie in the cage. Photo: EK Youngsteadt

After all, ants are notorious visitors to kitchens and picnics, and they are incredibly important scavengers and hunters in natural habitats all over the world (except Antarctica).

But it seems that I’m not the only one impressed by our tiny urban neighbors. Our study of garbage-eating ants was published today in Global Change Biology, and The New York Times, The Washington Post, National Geographic, and Wired have already published their versions of the story. More news in the works from Germany to South Korea, and I’ve described our study to more than a dozen reporters this week.

This process has been delightful and a little exhausting and even puzzling. I mean, sure, I was surprised when ants cleaned up the food the first time—but everybody else is amazed, too? It’s news that ants eat crumbs?

Or is it news that some scientists were nutty enough to weigh hot dogs and potato chips and set them out in experiments around the most densely populated city in the US–in Central Park, in the middle of Broadway, in view of the Statue of Liberty?

Or is it news that ants are competing with rats for this junk we drop? That this little drama plays out over the crumbs to which we never gave a second thought?

I’ll let you decide. Here’s what we found—the bullet-point version:

  1. Bugs in street medians ate two to three times more junk food than those in parks.
    Co-author Ryanna Henderson sampling a median. Photo: EK Youngsteadt

    Co-author Ryanna Henderson sampling a median. Photo: EK Youngsteadt

    Street medians are little strips of trees and groundcover planted between lanes of traffic, and they host fewer ant species than do parks. Ecological theory predicts that more diverse ecosystems are more efficient, so we were surprised that bugs in medians ate more than those in parks. We indulged in some extrapolation and calculated that the bugs inhabiting the 150 city blocks of medians on Broadway and West Street are capable of eating more than a ton of food per year–the equivalent of 60,000 hot dogs.

  1. Pavement ants (Tetramorium species E) are big eaters. We didn’t watch our cages for 24 hours to see exactly which species collected how many crumbs—but at sites where we found pavement ants, more got eaten. Pavement ants originated in southern Europe and the Middle East, but have been living in American cities for more than a century. They love nesting near pavement, so they’re more common in medians than in parks. (But Highbridge Park had them, explaining its big, median-like appetite.)
  1. Bugs compete with vertebrates (rats!) for our food garbage. Alongside our cages, we offered a second set of uncaged foods, available not only to bugs but also to any hungry vertebrate. More food got eaten from this open treatment than from the cage. That means that both groups of animals (bugs and vertebrates) want the stuff we drop. In other words, they compete for it; what one group gets, the other group doesn’t. I would love to know how much of that uncaged food went to ants and how much to rats–and whether that depended on the kind of food, the size of the food, the time of day, the habitat… But those are goodies for another study someday.
  1. Hurricane Sandy was a disaster, but not for garbage-eating bugs. Several of our study sites were inundated with saltwater during Hurricane Sandy, seven months before our study. We thought this would matter to the wildlife. But we detected no effect of flooding on how much food got eaten. Maybe there was still an effect on some kinds of bugs—we’re still figuring that out—but certainly not on those that eat our crumbs.

 

I admit I’ve often tossed an apple core into the woods, not even thinking of it as litter. It’s “biodegradable,” so it doesn’t count, right? Now, my friends, we have met our urban biodegraders. To them it counts, and their work behind the scenes is making our garbage disappear.

Comic by Dorit Eliyahu  https://sites.google.com/site/doriteliyahu/home

Comic by Dorit Eliyahu
https://sites.google.com/site/doriteliyahu/home

December 2nd, 2014|Categories: Feature, Lab Happenings, Natural History and Scientific Adventures, Urban Ecology|Tags: , |

Do scary parasites mean my yard is healthy?

This is a post by our Research Associate Elsa Youngsteadt about some rare parasites she found.

In a lab full of people quietly staring through microscopes, a startled yelp occasionally breaks the silence. And I admit, it sometimes comes from me. Diving into the magnified world can be a lot like watching a scary movie on a big screen.

Usually the freak-out happens when I’m doing something soothingly monotonous, like counting tiny scale insects on leaves. I get in a groove and forget that I’m seeing everything 30 times bigger than it really is. Then a spider dashes crazily across the field of view: It appears enormous, threatening, bristly, unpredictable, and very, very close. This is when the yelping happens. But of course the beast is actually smaller than a pencil eraser and nowhere near my face, so I feel silly, compose myself, and get back to the scale insects.

But sometimes, the startling thing is something I’ve never seen before, something wild and creepy and totally distracting. This is what happened earlier this year when I settled in to identify some newly collected bees from my yard. These were dead bees, mind you, fresh out of a cyanide jar and expected to sit still and not be startling.

The first few toed the line. There was a shiny, bulbous, blue-green mason bee, and a plain little matte-black sweat bee. A ground-nesting Andrena still had flakes of clay on her jaws. All normal and non-threatening.

Andrena bee with strepsipterans peeking out of its abdomen. Photo: Matt Bertone

Andrena bee with strepsipterans peeking out of its abdomen. Photo: Matt Bertone

Then, the yelp. Spreading across the rear end of the next bee was a mass of very alive, squirmy, maggoty little larvae, looking not-so-very little. I knew in split second what they were, but I admit to quickly popping the bee back in the cyanide jar to finish things off before looking again.

I was witnessing the birth of a brood of strepsipterans—a group of parasites whose wacky life cycle involves a weird, blobby insect eating a live bee from the inside out, while that insect’s own babies eat her from the inside. At the time I caught my bee, the strepsipterans had just finished feeding on their mother and emerged into the world, via a hole in their mama’s head (technically, in her cephalothorax). How else?

Had the bee avoided my net and continued to fly around visiting plants, the larvae would have hopped off on the next flower. (Really, hopped: Despite the initial maggoty impression, these are leggy, nimble little insect tykes.) Each one would have waited at the flower-airport to board a fresh bee, which would carry it back to an underground nest tunnel. There, the strepsipteran would find the bee’s egg or larva and burrow in—disappearing inside within a few hours.

The strepsipteran then loses its legs and eyes and grows along with its young bee host. Eventually it fills the bee’s abdomen, stunting its organs and altering its development. Female Andrena bees, for example, develop the angular cheeks and hairy abdomens typical of males. (They also become very hard to identify.) One researcher even reported finding a bee with a single, giant eye arching over its head like a headband–perhaps a strepsipteran-induced developmental glitch.

Strepsipterans emerging from Andrena bee abdomen. Photo: Andrew Ernst

Strepsipterans emerging from Andrena bee abdomen. Photo: Matt Bertone

As adults, male strepsipterans have wings and return the outside world to fly around for a few hours before they die. Females, however, remain ensconced in their bees, with only their heads visible from the outside. (That’s the smooth, yellowish tissue you can see sticking out of the bee’s abdomen in the photos.)

The rest of her body is “a great sack full of eggs,” wrote entomologist W. Dwight Pierce in 1909. The thousands of eggs simply float around inside the mother’s body, absorbing nutrients from her blood. Eventually, they hatch and trek to the outside world via the “brood canal” that exits their mother’s head. Which is where they were when they made me shriek.

This whole stranger-than-fiction setup is more than just a titillating insect freak-show. As parasites, strepsipterans may have an important role in maintaining insect diversity. Parasites tend to regulate their hosts’ populations in ways that prevent any one species from becoming outrageously common—leaving room for more species overall. That process keeps ecosystems diverse and food webs stable.

Stepsipteran larvae emerging. Photo: Andrew Ernst

Stepsipteran larvae emerging. Photo: Andrew Ernst

I would bet that strepsipterans are among the parasites that help maintain diversity, although their role has never been measured. There are about 600 species of strepsipterans in the world, and they can also be found in planthoppers, cockroaches, grasshoppers and wasps. In the bee and wasp species that have been checked, 10 to 30% of individuals carry strepsipterans and are unlikely to reproduce.

That means strepsipterans are common enough to regulate the abundance of their hosts. In a tantalizing example, the European paper wasp (Polistes dominula) left its strepsipterans behind when it moved across the Atlantic to North America—and none of the North American species will parasitize it. So researchers have suggested this wasp’s fast reproduction and dominance over native North American wasps may be due, in part, to the loss of its parasites.

Of course I have no way of knowing where my one bee with her alarming brood of squirmy strepsipterans fits into the big picture. But I’d like to think she’s a good sign. I’d like to think that if I kept looking I would find that my messy yard is teeming with a diversity of slightly creepy parasites, keeping their hosts in line and yielding an endless supply of microscopic scary movies.

November 25th, 2014|Categories: Feature, Natural Enemies, Natural History and Scientific Adventures, Pollinators|Tags: |