RESEARCH PROFILE: Hemlock Trees and their Pests

By Julia Brokaw and Vincent Waquiu

We got out of the truck at one of our research sites and saw two older women painting a picture of the forested road in afternoon sunlight. It was a beautiful scene, but what the artists didn’t know was that they were surrounded by stressed, thinning, and sick hemlock trees infested with the Hemlock Woolley Adelgid (HWA), the invasive insect pest currently attacking Eastern Hemlock Trees.

Hemlock trees are a ‘foundation species’ of forests. They are long-living, shade tolerant conifers that usually grow in groups or are assembled with other tree species. Hemlocks contribute to watershed quality and provide a unique micro-environment with a cool habitat for many species of birds, insects, and mammals. Since the 1950s, hemlock trees have been in a widespread decline due to the introduction of the Hemlock Woolly Adelgid from Japan. The HWA cause foliar damage, crown loss and mortality by inserting a feeding tube into the base of hemlock needles and suck the nutrients from the tree stem. They cover themselves with a white wool-looking substance where they lay over 200 eggs per wool sac.

More recently, researchers have seen even more stress on hemlock populations due to yet another invasive, non-native pest called the Elongate Hemlock Scale (EHS). The EHS differ from the HWA because they cause foliar discoloration by sucking nutrients directly from the hemlock needles and covering themselves in a waxy cuticle. Usually, a hemlock tree first becomes infested with the HWA and then with EHS soon after. 
 

This summer, our research asks if these two pests intensify the damage to hemlock, or slow hemlock decline due to competition for resources. To answer this question, we use a combination of field and laboratory work for research on the many elements contributing to this question. Out in the field with our mentor David Orwig, we go to different previously established plots that were designated as HWA infested, EHS infested, both HWA and EHS, or none. At these sites, we collect small pieces of the branches, called branchlets, to take back to the lab for analysis.

Under the dissecting microscope, these branches are telling an incredible story. You can see the tiny insects up close, the adelgids slowly, grossly throbbing on the needle base, covered in their wool. If you lightly pull back the wool cover, eggs that look like miniscule grapes poke out from the branch. The EHS are slimy, snot-like blobs on the leaves and bright yellow ‘crawlers’ hide beneath the covers. This week, we have been lucky to see the rare form of the adelgid life cycle: the winged male adelgids. Usually, the life cycle is considered “parthenogenic” which means that reproduction occurs without any males, and all HWA are females and produce clone daughters, but sometimes, winged males will emerge and fly away for dispersal purposes. These males often have trouble figuring out how to fly their wings! 

Another layer up close on the hemlock needles is the diverse world of microbes. Microbial communities are everywhere and contribute to many processes that people often take for granted. Microbial communities are made up of different fungi, bacteria, and other microorganisms that are major contributors to decomposition and nutrient cycling in all environments. This summer, we are going to study how these microscopic leaf communities change when the invasive pests are present. If these communities are changing, it has huge implications for forest processes on small (directly to individual trees) and large scales (nutrient cycling). We will research if the outer covering of these two insects (wool/wax) provide resources that enhance microbial abundance. We are currently finalizing our protocol for studying these microbial communities because this is fast growing area of science where new, better and more accurate techniques are being developed as we speak! 

Finally, we are studying the Carbon and Nitrogen atoms within these leaves. We collect the branchlets from different sites, measure the length, and count the number of HWA, EHS, or both. We then remove the needles and dry the needles and twigs in small coin envelopes. The needles or twigs are then made into a fine powder, and will be analyzed for their Carbon/Nitrogen ratio. In previous studies, they have found that trees with HWA are higher in nitrogen content, leading to changed soil chemistry (from needlefall), decomposition, and subsequently different understory habitats – a disruption of forest function. We are going to look at the Carbon to Nitrogen ratios for needles with EHS and both insects. This will give us insight into how these insects are interacting on the trees, and changing the chemistry of trees themselves as well as the overall forest systems.

It is hard to describe the feeling of walking through a stand of hemlocks but there is a deep of calmness and quietness about these forests. We feel lucky to be able to study and enjoy the beauty of these trees this summer because they are rapidly declining and may eventually disappear from our forests due to these pests. 

RESEARCH PROFILE: Pitchers and their Tipping Points

 By Jennie Sirota

My project for this summer studies the extraordinary carnivorous pitcher plant, Sarracenia purpurea. I am working with Aaron Ellison and Benjamin Baiser on a newly funded research project that studies the widespread issue of tipping points. Tipping points are the change from one state to another. These can occur in many different systems, such as in the atmosphere or even in the economy. While it is difficult to predict the changes, we study tipping points to attempt to prevent them from happening because it is energy and resource expensive to return from a change.

To test tipping points, we are looking at the aquatic micro-ecosystem within pitcher leafs of Sarracenia purpurea. The bacteria within the pitcher leaf can undergo a state change from aerobic to anaerobic when there is an overabundance of nutrients. We will be use the pitcher leaf as our model aquatic system to find the enrichment rate that produces the longest tipping period. With a long tipping period achieved through our tests, the next experiment can run tests to intervene and prevent this state change from occurring.

The first step in the experiment to discover is to gather the water from inside the native growing pitcher plants from Tom Swamp in Petersham, MA. This water contains the natural growing bacteria and other organisms that are unique to the pitcher plant and make up the micro-ecosystem within the leaves of the plant. The biggest challenge here is not falling into the bog! 

After we collect the water from the pitchers, we filter it to make sure it contains the aerobic bacteria. Then, we put this liquid into our pitcher plants in a greenhouse that mimics a natural field setting. From here, we can control variables that affect the plant, including the amount of nutrients that the plant receives. 

Enrichment levels are controlled by feeding the plants varying levels of wasps, a common prey for the pitcher plants in their natural environment. When a pitcher receives too much enrichment, it turns anaerobic. This means that the pitcher can’t take up carbon dioxide fast enough to supply sufficient oxygen to the organisms that decompose the prey. This is also known as a eutrophic state, similar to what happens in lakes when there are excess nutrients. 

After supplying different levels of enrichment to our pitcher plants, we measure the dissolved oxygen in the pitcher because the oxygen level is an indicator of when a state change has occurred. For example, 0% oxygen means the pitcher is anaerobic. The oxygen level is measured using oxygen probes that sit within the pitcher being tested. By tracking the changes, we can identify the enrichment rate associated with the longest tipping period before a change of state. 

Finding this enrichment rate is crucial to the next steps of the experiment. It will be used to apply management and prevention of a state change in a natural ecosystem. Following this, proteomic analysis will be done to find a reliable indicator that can give early warning before a state change. Then the unwanted state change could ultimately be prevented, and this process can be used in other natural systems. 

This amazing summer opportunity has already given me valuable experiences that I wont forget. I love working in a greenhouse and caring for carnivorous plants as I never thought I would be feeding plants!

RESEARCH PROFILE: Underground Photography of Root Growth

By Samuel Knapp 

I’m still shocked by the opportunity I have been given this summer. Being from the upper-Midwest, I was unsure what I would find when I arrived at the Harvard Forest. Much to my delight, the people of Massachusetts and Harvard Forest have been friendly and welcoming. The region is beautifully forested, and the surrounding communities live up to all the great things I’ve heard about New England culture (accents included). 

My research this summer at the Harvard Forest looks into the unseen world of roots, specifically the timing of their growth and decay. Trees allocate carbon to roots in the forms of cellular growth and carbohydrate storage, but the timings of these events are relatively unknown unlike above-ground processes of shoot and leaf development. Rates of respiration along with the chemistry of the roots and surrounding soil also fluctuate during these processes. The data we collect tracking root growth is fundamental to understanding tree systems, and therefore forest systems, as a whole.

As an undergraduate research intern, I have been trusted with a frighteningly expensive piece of equipment to conduct my measurements. What looks like a mortar shell on a long aluminum pole, the Minirhizotron camera is inserted into clear plastic tubes in the ground to take photographs of fine root systems as they grow, die, and decay. 

I am still amazed by this $30,000 piece of equipment that can capture high resolution images of roots as small as the width of a hair. With the many, many photographs I will take this summer, my mentor, Rose Abramoff of Adrien Finzi's lab at Boston University, and I will create quantitative measurements of when and in what amounts roots grow and die.

My experiences this summer, in addition to exposing me to the scientific process, have already shown me that I have a particular interest in design and construction of research equipment. I look forward with anticipation to what the rest of the summer holds: great friends, new places, interesting findings, and definitely more of our chef Tim’s uncannily delicious food!

RESEARCH PROFILE: Butterflies and Bumblebees

By Aubrie James and Kelsey McKenna

This summer, we’re studying animal movement with Dr. Elizabeth Crone and some of her “Cronies” (lab members and affiliates): post-doctoral fellow Greg Breed, Harvard OEB graduate student James Crall, and research intern Dash Donnelly. We’re looking at how anthropogenic landscape changes and resource availability affect population dynamics in two different organisms: bumblebees and butterflies. Since we’re both especially interested in morphological changes, we’ll sometimes stop fieldwork for a day and head out to the Concord Field Station in Bedford, MA where we’ll use high-speed cameras to examine insect flight in slow motion.

Butterflies with Aubrie

The organism I’m studying this summer is the Baltimore Checkerspot, a butterfly species in the family Nymphalidae. It’s also known as Euphydryas phaeton, Latin for “The cutest little butterfly on the planet. Or at least in Massachusetts.”  They haven’t emerged as butterflies this season, but they are starting to pupate.

 

Ahh, what a beautiful pupa! I’m studying the Baltimore Checkerspot with Greg (AKA Dr. Greg Breed AKA Butterfly Whisperer Extraordinaire AKA Best Mentor and he didn’t even pay me to say that).

Oh, there he is with Elizabeth! (AKA Dr. Elizabeth Crone AKA Fearless Leader of the Cronies). 

My main focus of study this summer is centered on the Baltimore Checkerspot’s food when they are in their larval stages. Back in The Dark Ages, (or, before my dad was in high school) the Baltimore Checkerspot exclusively used a plant called the White Turtlehead to lay eggs and munch on. However, our Checkerspots have recently been using a "weedy" plant called the English Plantain for the same purposes as the White Turtlehead.

This is a blurry picture featuring a larva and my sparkly nail polished finger! I tried to catch another picture, but right after this was taken, Greg said “Aubrie, you’re rolling around in a big patch of Poison Ivy.” Fieldwork is cute like that.

Anyhow, the Plantain has become more pervasive in the Checkerspot’s habitat mainly due to anthropogenic changes in the landscape. The Checkerspots, being the pragmatic little guys they are, have started incorporating the Plantain into their life history, and have experienced somewhat of a population boom.

Yum!

With this broadening of the Baltimore Checkerspot’s larval diet, I’ll be studying how the change in diet – Turtlehead (Chelone) versus Plantain (Plantago) -- affects the flight ability of adults. I’m going to be really busy this summer, both in the field and in the lab, but this is truly the best gig on the planet.  I’m learning, I’m researching, I get to hang out with geniuses every day, and my job duties are the following:

1.      Read a lot of articles about butterflies

2.      Chase butterflies around meadows with a big net 

3.      Mark butterflies with glitter gel pens

4.      Use a high speed camera to film butterfly flight

5.      Repeat

I really don’t think it gets better than that (even though I'd be okay with a little less Poison Ivy).  

 

Bumblebees with Kelsey

I’m spending my summer studying Bombus impatiens, or the impatient bumblebee, which is a common species in the Harvard Forest. This summer’s large experiment investigates how temporary food surpluses, or resource pulses, affect bumblebees when occurring at different points of the bees’ colony cycle. Colonies given an early resource pulse (like the typically early bloom of the forest canopy) could produce larger and more viable workers, and more queens at the end of the summer. I’m interested in how differences in size between bees of the same species, or even the same colonies, affect where bees are more likely to forage due to differences in flight energetics. 

After a few weeks of prep, we have started the big resource pulse experiment. First, we mark the bees with colored paint pens so we can identify each bee by its hive and approximate life span. 

Then, we set up clear tubes from our hives to these big structures, called hoophouses, which are full of flowers. 

After pouring some sugar water down the tubes, we can observe bees flying through the tubes to their resources in the hoophouses and bringing pollen back to the hive. Last week was my first time seeing the bees hard at work, flying through the tubes!

Last week brought another exciting event when we also had Drew Faust, the President of Harvard University, visit the forest. She stopped by our field site to see the bees on her tour. 

I’ve had a lot of fun learning to work with bees (especially because we’re three weeks in and I still haven’t gotten stung). I work with Dash everyday and he is starting to teach me how to identify the pollen we find on our bees.

RESEARCH PROFILE: Providing Safe and Clean Water

By Tefiro Kituuka Serunjogi

This summer I will work with Dr. Betsy Colburn to advance a research project I started in high school. The objective of my original project was to investigate ways in which hygienic and clean water could be provided to the people of my local community back home in Uganda.

My goal this summer is to build an implementable prototype of a filtration system and then test it for effectiveness, reliability and efficiency. Through my tests, I will look at how well the system purifies water, the life span of the system, and the logistics involved in maintaining the system.

My filtration system consists of a top layer of fine sand and two smaller bottom layers of gravel and small rocks. The inertial and centrifugal forces of the sand grains act upon particles in the water at a specific gravity higher than that of the surrounding water forcing these particles to leave the flow lines and deposit in the crevices (gaps) between the sand grains. As a result, the water is made free of inferior substances such as soil and dirt. The fine sand and other media (gravel and stones) need to be washed and properly cleaned before setting up the filter.

The next level of purification is exposure of the filtered water to sunlight. The sun’s ultraviolet radiation is effective in killing off several pathogens. Temperature rises due to sunlight exposure also help kill off some pathogens.

I will also investigate different design modifications with the objective of determining how and whether the system can be customized for both large scale (community) use and for small scale (personal/family) use. My initial small scale prototype has already produced some really good results in terms of the removal of turbidity from the water.

It should be an exciting rest of the summer and I hope that someday the work I do here will help better the lives of the people in my local community and others around the world.

“Access to safe water is a fundamental need and, therefore, a basic human right. Contaminated water jeopardizes both the physical and social health of all people. It is an affront to human dignity.” – Kofi Annan, ex-UN Secretary-General