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

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.

Japanese maple scale

Japanese maple scale, Lopholeucaspis japonica , is active now and much of the summer. It is a small, oystershell-shaped, armored scale introduced to the U.S. from Asia. Japanese maple scale is found in several eastern U.S. states, including CT, DE, GA, KY, MD, NC, NJ, PA, RI, TN and VA, as well as Washington D.C.. Japanese maple scale has a wide host range that in addition to maples (e.g., Japanese maples, Red maples, Paperbark maples, and sugar maples), includes Amelanchier, Camellia, Carpinus, Cercis, Cladrastis, Cornus, Cotoneaster, Euonymus, Fraxinus, Gledistia, Ilex, Itea, Ligustrum, Magnolia, Malus, Prunus, Pyracantha, Pyrus, Salix, Stewartia, Styrax, Syringa, Tilia, Ulmus, Zelkova, and others.

Brian Kunkel, University of Delaware, Bugwood.org

Brian Kunkel, University of Delaware, Bugwood.org

Although the lifecycle of this pest has not been fully examined, two generations a year are expected in the mid-southern U.S. First generation crawlers emerge in mid-May, and the second generation in early August  but there may be more. Management efforts are complicated by the extended crawler emergence that results in first and second generational overlap. Thus, the most recent sample we received had every stage – egg to adult- present at the same time.

Adult scales and crawlers are very small and most readily observed on bark of dormant deciduous host plants, but can also be found on foliage. The waxy coating on the body of male Japanese maple scales is white and females, eggs, and crawlers are lavender. The most work on this scale has been done by Paula Shrewsbury and Stanton Gill at the University of Maryland. There is also information on JMS and other maple pests in our new book here: http://ecoipm.com/extension/extension-resources/

A link to the UMD fact sheet is here: http://ipmnet.umd.edu/nursery/docs/JapaneseMapleScale-UMD2011.pdf

 

Protect these soft scale predators

Hyperaspis binotata is an important natural enemy of soft scales in eastern US. It

Hyperaspis binotata adults from Simanton, 1916.

Hyperaspis binotata adults from Simanton, 1916.

particularly came to the attention of researchers trying to control terrapin scale on orchard trees in the early 20th century. It feeds on lecanium scales, Pulvinaria scales such as cottony maple leaf scale, tuliptree scale, terrapin scale, and others. There are many other lady beetles that feed on scale insects. Hyperaspis is a large genus of small lady beetles that feed on scale insects, aphids, and mealybugs.

They typically are black with red or yellow markings. They can be difficult to distinguish from each other. A similar species is the twice stabbed lady beetle, Chilocorus stigma, which is common around scale infestations but larger than Hyperaspsis species.

The larvae are covered in white wax making them look something like mealybugs. I found some feeding

IMG_0774

Hyperaspis larvae on tuliptree scale. Photo: SD Frank.

on tuliptree scale in Asheville last year. Its important to recognize these so you don’t think you have a double infestation of scales and mealybugs. Its easy to tell the difference since they move much faster than mealybugs (meaning that they actually move).

Hyperaspis binotata occurs throughout eastern North America. Beetles overwinter at the base of infested trees and leaf litter. They emerge from hibernation in early spring around the time many of its prey also resume feeding and development. Eggs are deposited singly near scales. The H. binotata life cycle requires about 39 days to complete.

Twice-stabbed lady beetle on a red maple covered in gloomy scales. Photo: SD Frank.

Twice-stabbed lady beetle on a red maple covered in gloomy scales. Photo: SD Frank.

A single Hyperaspis larvae may consume up to 3000 terrapin scale nymphs to complete development. They are probably critical to regulating scale insect abundance in natural habitats. We are not sure how well they perform this service in urban areas. Hyperaspis spp. and other natural enemies are killed by many insecticides. Protecting natural enemies can be critical to reducing urban scale insect outbreaks as seen during wide-spread spray campaigns to control nuisance flies or landscape pests.

Hyperaspis binotata larvae from Simanton, 1916.

Hyperaspis binotata larvae from Simanton, 1916.

More information and pictures are on Dr. Mike Raupp’s ‘Bug of the Week’ website: http://bugoftheweek.com/blog/2013/1/7/waxy-ladies-hyperaspis-lady-bugs and in the publication by from which I copied the pictures above.

Simanton, F.L. 1916. Hyperaspis binotata, a predatory enemy of the terrapin scale. Journal of Agricultural Research, vol. VI, no. 5, pp. 197-204.

 

Tuliptree scale primer

If you haven’t met tuliptree scale, Toumeyella liriodendri, its high time you did. I found

Tuliptree scales on tulip poplar twig. Photo: SD Frank

Tuliptree scales on tulip poplar twig. Photo: SD Frank

dense patches of it at a local playground the other day. I was tipped off by honeydew, which can mean tulip poplar aphids, but also scales. Tuliptree scales feed primarily on tulip poplar, Liriodendron tulipifera, though it is occasionally found on other trees including Magnolia spp. It occurs throughout the eastern US from New England to Florida.

Unlike many other soft scales in our area, tuliptree scale produces crawlers at the end of summer and into fall. The scales overwinter as 2nd instars on twigs. In spring they develop to adults and produce lots of honeydew throughout the summer. In late summer honeydew production declines as female scale begin producing eggs and crawlers. A single female can produce over 3000 crawlers over three months. This could make control difficult since you cannot target a whole cohort of crawlers with a single application of oil or insecticide.

Honeydew from tuliptree scale supports dozens of other species. Researchers have recorded 93 hymenopteran species that collect honeydew of tuliptree scale and a dozen or so ant species. This is an amazing diversity of creatures that would not be in a tree if these scales were absent. This disproportionate effect of one species on the animal community

Distribution of tuliptree scale as of 1969 from Burns & Donlely 1970.

Distribution of tuliptree scale as of 1969 from Burns & Donlely 1970.

suggests a potential foundational or keystone role. Since these scale produce so much honeydew they can be heavily tended by ants. Ant tending can reduce scale mortality by predators and increase scale abundance.

Tuliptree scale cause considerable damage to trees. They can kill central leaders resulting in bushy plants with codominant leaders. They can kill trees or reduce tree growth rate. High densities of scales can remove more carbon than a tree produces. In this case trees are surviving on reserved energy that is gradually depleted.

Reference: Burns, DP, Donely, DE. 1970. Biology of the Tuliptree Scale, Tourneyella liriodendri (Homoptera: Coccidae). Annals of the Entomological Society of America, 63, 228-235.

 

 

Euonymus scale

Somehow I got this far in the season without posting anything about euonymus scale.

Euonymus scale

Euonymus scale on a heavily infested leaf. Photo S.D. Frank

Maybe because this is the first year I have not been conducting research on it or writing papers about it. Euonymus scale has three generations per year in North Carolina the first of which occurs around May. It is best to treat euonymus (or any) scale in the crawler stage. So if you forgot in the spring or didn’t get sufficient control (or were waiting for an alert from me) you still have a chance. Crawlers are active at sites on campus and in Raleigh neighborhoods. In the first generation crawlers come out all at once but become less synchronized in second and third generations. Thus you may find all developmental stages present at this time. There are a number of products that can be used to treat armored scale. You can read an article in Nursery Management about scale control here. Our research (published here) has found neonicotinoids Safari, Flagship, and TriStar to be very effective and also plant growth regulators Distance and Talus. Note that imidacloprid is not labeled for, or effective against, armored scale. Please check the updated insect note for recommendations http://www.ces.ncsu.edu/depts/ent/notes/O&T/shrubs/note15/note15.html

Amazing parasitoid wasps emerging from scales

This guest post is by PhD Candidate Emily Meineke.

Oak lecanium scale Parthenolecanium quercifex on willow oak. Photo: EK Meineke

Oak lecanium scale Parthenolecanium quercifex on willow oak. Photo: EK Meineke

Parasitoid wasps are often effective at keeping pest populations below damaging levels. Five parasitoid species attack oak lecanium scale, one of the two most damaging pests on urban oak trees in the Southeastern US. Besides being lovely to look at, these parasitoids reduce the number of eggs oak lecanium scales produce, which means they help the trees.

Encyrtus fuscus emerging from oak lecanium scale in Raleigh, NC in May 2014. Photo: EK Meineke

Encyrtus fuscus emerging from oak lecanium scale in Raleigh, NC in May 2014. Photo: EK Meineke and Andrew Ernst.

Oak lecanium parasitoids are emerging right now in North Carolina. So are oak lecanium crawlers, which are more responsive to pesticide treatment than any other life stage. Our research shows one of the most effective parasitoid species, Encyrtus fuscus, is active right now on leaves. I observed them last week lapping up honeydew and oak lecanium crawlers.

 

Many studies show spraying when natural enemies are active can lead to pest outbreaks, which leaves us in a bit of a pickle when it comes to oak lecanium treatment. However, our research shows that on the hottest urban trees the parasitoids and other natural enemies are not keeping up with scale abundance. On these trees horticultural oil applications during crawler emergence could help reduce scale abundance without last effects on parasitoids and other natural enemies.

Encyrtus fuscus searching a willow oak leaf. Photo: EK Meineke

Encyrtus fuscus searching a willow oak leaf. Photo: EK Meineke