Cities as a glimpse of the future

This is a guest post by our Research Associate Elsa Youngsteadt about the work and meaning behind her new research published in Global Change Biology.

About a year ago, I found myself sitting ruefully in a patch of chiggery grass by the side of the road near the little town of Bahama, North Carolina, waiting for a tow truck. I had stuck the lab pickup firmly in a ditch. It was tilted at an embarrassing, sickening angle and had one wheel lodged against the mouth of a culvert. Helpful passers-by with chains and four-wheel drives kindly offered to pull me out, but really only made matters worse.

My memory is already fuzzy about the sequence of events, but somewhere in there—

Gloomy scales and the beetle that loves them. Each white or gray bump is a gloomy scale. The twice stabbed lady beetle is one of their predators. Photo: S.D. Frank

Gloomy scales and the beetle that loves them. Each white or gray bump is a gloomy scale. The twice stabbed lady beetle is one of their predators. Photo: S.D. Frank

between slipping into the ditch, the failed rescue attempts, and the final arrival of the giant tow truck—I did actually hike into the woods and get what I came for: eight slender red maple branches, clipped from trees growing in NC State’s Hill Forest.

I found my way to this particular spot, ditch and all, by following the trail of a plant biologist who had collected maple branches there more than 40 years ago during the height of the Nixon administration and the Vietnam War. In those days, the forest was cooler. The fevered dog days of summer now average about 1.4 degrees C (about 2.5 degrees F) hotter than they did then—and that should make a difference to the trees and the insects that live on them.

Specifically, it ought to make a difference to gloomy scale insects. These little sap-sucking insects seem to like it hot. My colleague Adam Dale has been studying gloomy scales in the city of Raleigh, and he’s found that street trees in the hottest parts of the city have far more scales—sometimes 200 times more–than those in the cooler parts of the city.

The scales drink tree juices, so more scales are bad for trees. A couple of degrees

Sad, bedraggled, gloomy scale infested red maple trees. Photo: SD Frank

Sad, bedraggled, gloomy scale infested red maple trees. Photo: SD Frank

warming can make the difference between a stately shade tree and a sad, bedraggled specimen with dead branches, sparse leaves, and grimy, scale-encrusted bark.

We thought that if warming gives scales such a powerful boost in the city, global warming could do the same thing for scale insects in rural forests. But we still had no direct evidence that what happens in the city represents what happens in rural areas over time.

This seemed like hard evidence to get. Unlike birds and butterflies, the drab, millimeter-long gloomy scale has not invited enthusiastic long-term monitoring. But perhaps we could scavenge scale-insect information from another source—and this is why I became extremely grateful to scores of plant biologists like the one who archived a foot-long maple twig from Hill Forest in 1971.

These historical plant specimens are stored in collections known as herbaria, where they are affixed to stiff pieces of paperboard, labeled, and stacked in mothball-scented cabinets. It turns out that many of these old twigs still have scale insects intact, stuck firmly but inconspicuously to the spots where they once lived.

An herbarium specimen used in the study. Photo: EK Youngsteadt

An herbarium specimen used in the study. Photo: EK Youngsteadt

It made perfect sense that they would be there, but it still felt outlandish when, only 12

branches into my first search in the UNC Herbarium, there was a gloomy scale—the same species that burdens our urban red maples. It was beautifully preserved, looking like it was collected last week instead of 30 years ago. Even on 100-year old branches, the scales looked perfect.

So I counted them. And kept counting them on more than 300 historical specimens from the southeastern US, then matched up their abundance with historical temperatures for the year and location where each specimen was collected.

There it was: During relatively cool historical time periods, only 17% of branches had scale

Gloomy scale covers preserved on an old herbarium specimen. Photo:EK Youngsteadt

Gloomy scale covers preserved on an old herbarium specimen. Photo:EK Youngsteadt

insects. But during relatively hot periods, 36% were infested. In other words, scale-infested branches were more than twice as common during hot periods than cool periods—exactly as we would expect if scale insects benefit from warming in rural forests as they do in the city. Furthermore, the most heavily infested twigs were ones that had grown at temperatures similar to those of modern urban Raleigh.

But the historical specimens weren’t the whole story. The past several years have been warmer than even the historically warm time periods, so to test our prediction, we needed to go back to places where those old branches were originally collected, and see if their scale infestations had actually gotten worse.

Thanks to the careful records of those past plant collectors, I was able to track down 20 of the forest sites across North Carolina where red maple branches were collected in the ‘70s, ‘80s, and ‘90s (and only put the truck in a ditch at one of them). At 16 of the 20 sites, gloomy scale populations were denser than they were on the original branches from the same locations. Overall, I found about five times more scales in 2013 than in the earlier decades.

Careful records and herbarium tags from the past helped Elsa relocate the collection sites. Photo: EK Youngsteadt

Careful records and herbarium tags from the past helped Elsa relocate the collection sites. Photo: EK Youngsteadt

This isn’t good news, but it’s also not time to panic about gloomy scales killing our forests. Although the rural scale insects clearly benefited from warming, just as they do in Raleigh, they still never got as abundant as the ones we see in town. The reasons for that difference are an open question (I have some guesses, but that’s a different story). So, although I’d put money on gloomy scales getting more common in rural North Carolina over the next several decades, I wouldn’t yet say how much more common.

But this really isn’t just about gloomy scale. It’s about cities as an advance guard of climate change. If we can look at scales’ response to urban warming and correctly predict their increased abundance due to global warming, can we do it for other organisms, too? Can we do it for functions, like pollination and biological control of pests?

I hope we can start watching urban ecosystems for problem insects and using that information to stand forewarned about future ecological changes in natural areas. The experiments we have made by paving our cities and making them heat up may have much more to tell us about how organisms will handle future warming.

This post is based on a new study:

Youngsteadt, E., Dale, A.G., Terando, A.J., Dunn, R.R. and Frank, S.D. 2014. Do cities simulate climate change? A comparison of herbivore response to urban and global warming. Global Change Biologydoi: 10.1111/gcb.12692.  PDF

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Orange-striped oakworms make yearly appearance

This is a quick field note by PhD student Emily Meineke.

For the last few weeks, orange striped oakworms have been raining on my head as I work in the trees. They also drop a lot of

 

 

Large oakworms eat entire leaves except for the mid vein. Photo: EK Meineke

Large oakworms eat entire leaves except for the mid vein. Photo: EK Meineke

poop (entomologists call it frass) which is one of the major complaints by homeowners. Orange-striped oakworms congregate on branches to feed every year in late summer but usually do not cause enough damage to warrant treatment.

Young oak worms cause damage called 'window panning' in which they eat the surface of leaves and feed between tiny veins. Photo: EK Meineke.

Young oak worms cause damage called ‘window panning’ in which they eat the surface of leaves and feed between tiny veins. Photo: EK Meineke.

Young orangestriped oakworms are often light in color and darken as they get older. I have found some parasitized individuals, which means natural enemies are doing their part to reduce oakworm outbreaks. Caterpillars also make great food for birds. We have posted previously about orange-striped oak worm biology and management if you want more information.  

Large caterpillar poops around the base of a tree. Photo: SD Frank

Large caterpillar poops around the base of a tree. Photo: SD Frank

Urbanization is good for pests and bad for trees

My wife is from a neighborhood outside Baltimore called Lawyer’s Hill. This is where, in the 18th century, lawyers (and I assume doctors and other gentlemen) had country houses and could escape the summer heat. Lawyer’s Hill is only 3 miles from Baltimore but, based on their significant investment in houses and land, it must have provided significant relief. So what was (and still is) the difference between Baltimore City and Lawyers Hill? Trees.

Historic Lawyer's Hill (left) and downtown Baltimore City. Images from Google Maps.

Historic Lawyer’s Hill (left) and downtown Baltimore City. Images from Google Maps.

Trees cool the environment by shading houses, roads, and sidewalks that absorb heat. If

Damage by gloomy scales. Notice dead branches and sparse canopy. Photo: SD Frank

Typically shabby red maples with damage by gloomy scales. Notice dead branches and sparse canopy. For more (better) pictures visit Adam’s picture gallery featured in the Bulletin of the Ecological Society of America. Photo: SD Frank

you have every walked barefoot from the pool (or wherever you spend time barefoot) to your car you know that pavement is hot and that you scurry from one patch of shade to another. All the heat absorbed by pavement that does not radiate into the soles of your feet radiates into the air. Trees also cool the environment by evaporative cooling called transpiration in which they release water vapor through their leaves. Of course there are other reasons cities are hot. Air conditioners, industrial processes, and vehicles all generate heat. An unshaded bus stop is hot but even hotter when the bus is idling next to it.

All this heat can be bad for people. Heat alone poses a risk to human health as does exposure to solar radiation and pollutants that become more concentrated in hot areas. So why don’t cities plant more trees? Many of them do and try to preserve the trees they have. Unfortunately, arthropod pests are more abundant on urban trees and urban tree survival is low.

In two papers released today, Adam Dale, PhD student extraordinaire, has tackled the questions of why herbivores are more abundant on urban trees and what are the consequences for urban tree health. Adam works on gloomy scale, Melanaspis tenebricosa, an armored scale that feeds on almost every red maple within city limits (go look at the closest red maple, then get back to work).

All the gray bumps on this trunk are gloomy scales sucking nutrients from the tree. Photo: SD Frank

All the gray bumps on this trunk are gloomy scales sucking nutrients from the tree. For more (better) pictures visit Adam’s picture gallery featured in the Bulletin of the Ecological Society of America. Photo: SD Frank

In his first “Urban warming trumps natural enemy regulation of herbivorous pests” published in Ecological Applications he shows that urban warming seems to be the primary factor associated with gloomy scale abundance on urban trees. He supports this by identifying an amazing physiological mechanism: scales at warm sites can have 3 times as many babies as scales at sites just 2.5 degrees cooler!

Adam came up with a way to count gloomy scale embryos to determine that warm scales produce more babies. Photo: AG Dale

Adam came up with a way to count gloomy scale embryos to determine that warm scales produce more babies. For more pictures of scale embryos visit Adam’s picture gallery featured in the Bulletin of the Ecological Society of America. Photo: AG Dale

Adam’s next question was: So what about the trees? Do scale insects and temperature increase plant stress or reduce tree growth? This is what urban foresters need to know if they are going to make management decisions. Why manage scales if the heat kills trees anyway? Adam’s second paper “The effects of urban warming on herbivore abundance and street tree condition” in PloS One shows that both scale insects and heat are associated with poor tree condition. This means trees with scales and particularly hot trees with scales are more likely to have dead branches, sparse foliage, and generally look worse that cool trees without scales.

Urbanization is increasing and a new paper from Adam Terando and colleagues from NCSU and the USGS Southeast Climate Science Center suggests urbanization will expand more than previously thought. See a piece on The Rise of Charlanta by Rob Dunn. You notice in the image of Lawyer’s Hill that subdivision construction is underway. Each of these house will get a lollipop tree, probably a red maple or worse an ornamental plum, but the canopy will never be restored. To conserve trees and their valuable benefits for human and environmental health we need to understand even more about why pests become more abundant on urban trees and which trees should be planted to establish resilient urban forests. Its clear from Adam’s work that red maples are not a good choice for hot southern cities.

A gallery of photographs of Adam’s research was featured in the Bulletin of the Ecological Society of America.

Sweat Bees like YOU Sweaty!

Guest blog by April Hamblin an MS student in our lab who is often sweating in the urban heat as she conducts research to determine how urbanization affects native bee communities. She writes periodic posts here and on yourwildlife.com about her research and bee natural history.

Do you sweat in this North Carolina heat and humidity? If you sweat enough, beautiful bees may come by and give you a light kiss. These bees in the family Halictidae are known as sweat bees because they drink the salts from your sweat. They are very small and often mistaken as flies. If swatted at, many have stingers so small that they cannot penetrate our skin, but if they do, you may feel a tiny twinge of pain that soon leaves as fast as the bees fly away. So when you’re outside this summer sweating up a storm, watch for your friend and important pollinator, the sweat bee.

Augochlora_pura_Bee

While many sweat bees are dark black and blue, some are even green! This common species, Augochlora pura, is found in North Carolina along with over 500 species of native bees! In this photograph, this sweat bee is extending her tongue to the left, which is how she would suck the salts from your sweat. Photographed by Sam Droege, USGA. For more beautiful photographs of native bees, please visit: https://www.flickr.com/photos/usgsbiml/

When fieldwork fails….

Musings on fieldwork by PhD student Emily Meineke who spends a lot of time in the field with her trees – and by ‘field’ we mean downtown Raleigh. When the equipment doesn’t cooperate she can still enjoy nature. 
Everything takes longer than I think it should– we all suffer from this, yes?– so when field

Bee digging for pollen. Photo: Emily Meineke.

Bee digging for pollen. Photo: Emily Meineke.

Beautifully patterned cricket. Photo: Emily Meineke.

Beautifully patterned cricket. Photo: Emily Meineke.

An unfortunate tussock moth covered in parasitoid pupae. Photo: Emily Meineke.

An unfortunate tussock moth covered in parasitoid pupae. Photo: Emily Meineke.

Tussock moth caterpillar sans parasitoids. Photo: Emily Meineke.

Tussock moth caterpillar sans parasitoids. Photo: Emily Meineke.

work this week dragged on but gave no results, I decided to stare at insects instead. Elsa Youngsteadt, a research associate in the Frank lab, and I set out to measure, as Elsa puts it, how well trees breathe, make food, and turn that food into tree. In other words, we’re measuring photosynthesis.

The measurements require a fancy machine, which is impressive in its fanciness but requires finessing. Elsa knows how to finesse it. I barely know how to look at it right. But we were both newly introduced to it and have spent the last 5 mornings from 7 am trying to make it tell us to what extent city trees are breathing.
Some small thing always goes wrong, and we’ve gotten exactly 0.00 measurements. This is not a complaint. It is a fact, one that we will try to remedy at 7 am again tomorrow (Sunday) morning with patience. But this morning, I had none left, so I took photos of a handful of the the many insects we’ve seen while waiting for the machine to “equilibrate” or “become happy again”. We’ve seen sand wasps stinging prey to take back to their nests, native bees, daddy long legs with red mites on their legs, ants, butterflies, crickets, termites, scale insects, trash bugs, bark lice, furry caterpillars, and the list goes on.
The patience required by this fancy machine and its temper tantrums has reminded me that if you just sit in one spot, a parking lot, a construction site, a back yard, the earth will rise in its many forms, to remind you (me) that things around you breath whether you measure it or not.

Leaf cutter bee damage and conservation

I have gotten several phone calls about leaf notches on redbud trees. This characteristic damage is caused by leaf cutter bees in the genus Megachile. Leafcutters in Megachile

Leafcutter bee. Photograph by Sam Droege, USGS

Leafcutter bee. Photograph by Sam Droege, USGS

and other genera are solitary bees that nest in hollow grass stems or other pithy stems they can easily excavate.  They will also make nests in existing holes in wood but do not bore their own holes in wood (those are carpenter bees). Adult leaf cutter bees can be about as big as honey bees. They cut out round pieces of leaves to line their nests and pack in between brood cells. Damage by leaf cutter bees is general insignificant. In this area they seen to prefer

Leaf notches cut by leafcutter bees on a redbud tree. Photo: S.D. Frank

Leaf notches cut by leafcutter bees on a redbud tree. Photo: S.D. Frank

redbuds but will cut other plants including maples and roses. I have never seen more than a few leaves damaged on any particular tree and the damage is not enough to affect tree growth or health. Leafcutter bees are important pollinators of many native plant species and fruit and vegetable crops. In many urban and rural areas the plant species bees use for nesting have become less common than they used to be. Thus, bees cannot find suitable reedy grasses of tree holes to nest in. You can help conserve leaf cutters and other bees species by creating nest tubes.  These are fairly simple contraptions that just require tying together bundles of reeds or drilling holes in blocks of wood to replace the nest substrate that used to be provided by plants. Visit April Hamblin’s other recent blog post for details. April is conducting research on how urbanization and urban warming affect bee communities, individual survival, and nesting. Visit her guest blog on yourwildlife.com or project description for details of her work.

Leafcutter bee nest with cells divided by rolled up leaves. Each cell holds a pollen ball and one egg to develop into an adult bee one day. These bees are also solitary. Photograph by Joel Gardner, Wild Bees and Building Homes.

Leafcutter bee nest with cells divided by rolled up leaves. Each cell holds a pollen ball and one egg to develop into an adult bee one day. These bees are also solitary.
Photograph by Joel Gardner, Wild Bees and Building Homes.

Overall leafcutter bees are far more beneficial than harmful (they also rarely sting unless handled). My suggestion is to tolerate the subtle damage these bees cause and use it to teach other people about bees.  If you are growing plants for sale you may not be able to do this but I rarely see leaf cutting on nursery stock.

MS student April Hamblin contributed to this post.

Bee condos for bee conservation

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

If you haven’t heard the news already, the White House is creating a Pollinator Plan to help create new pollinator habitat.

But habitat for bees does not have to stop (or start) there—YOU can create bee habitat in

Osmia atriventris, or a Mason Bee, is one of many bees that will inhabit bee condos. These blue beauties use a combination of mud and leaf pulp to construct their homes. Photograph by Sam Droege, USGS.

Osmia atriventris, or a Mason Bee, is one of many bees that will inhabit bee condos. These blue beauties use a combination of mud and leaf pulp to construct their homes. Photograph by Sam Droege, USGS.

your very own back yard! Planting more native flowers is a great start, but if you have already landscaped your yard to the hilt or just want to do something simple, bee condos (as my dad calls them) are just the thing for you.

Native bees live in many areas materials.  Many species live in the ground such as the small andrenids that come out early each spring. Others make nests in hollow twigs, reeds, or holes in rotten wood. Unfortunately, many of these materials are less abundant in urban yards than in natural areas.

Bee condos use bamboo and other natural reeds to replace these plant materials and create five star living for native bees. But don’t worry, these bees don’t excavate holes to live in. They are also solitary, which means that they live alone instead of socially like honey bees. They have a mild temperament (as long as kids don’t stick their fingers in the nest) and would not become a pest in your home, but a friendly neighbor pollinating your garden. North Carolina has over 500 native bee species! For more beautiful native bee photos visit: https://www.flickr.com/photos/usgsbiml/

Osmia atriventris, or a Mason Bee, is one of many bees that will inhabit bee condos. They come out early in the season, so put up your bee condos in early spring if you want these blue beauties. Mason bees use a combination of mud and leaf pulp to construct their homes. Mason bees separate brood cell in their nests with mud. Each cell holds a pollen ball and one egg to develop into an adult bee one day.

Osmia nest packed with mud and brood. Photograph by Joel Gardner, Wild Bees and Building Homes.

Osmia nest packed with mud and brood. Photograph by Joel Gardner, Wild Bees and Building Homes.

Megachile spp. or leaf cutter bees, will also live in the bee condos. Leafcutter bees fly all summer, so if you get a late start, you will get these fuzzy bees. Leafcutter bees construct their nests with leaf fragments they cut with their powerful mouths, or mandibles.

You can create a bee condo with inexpensive readily available materials. All you have to do is:

  1. Cut bamboo or natural reeds where they are segmented so one side will be open
    Close up of reeds in a bee condo in various stages of colonization. Photo: April Hamblin, NCSU

    Close up of reeds in a bee condo in various stages of colonization. Photo: April Hamblin, NCSU

    and the other will be closed (inside hole diameters around 1/8 are most popular).

  2. Zip-tie 30+ pieces of bamboo and place them somewhere sturdy: on a tree, strapped to a metal post, near the shed, etc.
  3. Painting the outside of the bamboo white and/or blue is a great idea to help bees find their way to their new home. This is a great project for all ages and helps native bees find a home for them and their young.
  4. The bee condos are only good for one season though, so you’ll have to make this a family tradition! Remember to be as simple or creative as you want. Bee condos can just be bamboo bundles, a coffee can, or as decorative as bird houses. It’s up to you and your family!

For more detailed instructions on how to create a bee condo please visit Joel Gardner’s

April at one of her research sites.

April at one of her research sites.

Wild Bees and Building Houses.

I have been using bee condos in my research at 20 homes just like yours to determine how aspects of urbanization affect bee communities and nesting. The volunteers tell me seeing the busy bees fly about their business is fun for the whole family and helps us remember the beauty and importance of nature which is too often forgotten.