Tent caterpillar infestation. Photo courtesy of Ronda Jones.
The Orcas Middle School Science Club was looking for a good indicator of toxic accumulation in the recently completed constructed wetland in Eastsound. After trying a number of different kinds of traps for flying and aquatic insects, none of which collected much testable biomass, the solution—well—simply dropped on them.
As toxic chemicals from motor vehicles wash off roads and into the recently built detention ponds, some of the contaminants will stick to clay and organic matter and stay on the bottom. Trees and shrubs around the ponds may take up some of the contaminants and could spread them to insects and birds eating leaves, flowers and fruits. Monitoring changes in the amount of pollution leaving the ponds this way is technically challenging, explains Kwiáht ecologist Russel Barsh, who advises the science club. Indicator species must be found that are abundant but short-lived, accumulate toxics quickly from wetland plants they eat, and are easy to collect and extract.
Tent caterpillars should be excellent indicators, he says. They eat voraciously and convert many times their own weight in leaves into body fat each day for up to six weeks before they pupate. Even very small amounts of pollution in plants should be detectable in the body fat of tent caterpillars.
Extracting caterpillars is “really gross,” science clubbers agree, but the result is a clear green liquid that reflects the kinds of plants each caterpillar was eating. Individual caterpillars are quick frozen, ground up into a paste with powdered silica and methanol is squeezed through the mixture under high pressure. Toxic compounds dissolved in body fats are extracted into the methanol; the fats stay in the silica.
Science clubbers decided to focus on PAHs (polycyclic aromatic hydrocarbons) because they are found in gasoline, motor oil, road tar and automobile exhaust, and can be highly carcinogenic. Antibodies are used to determine the amount of PAHs in extracts from insects and shellfish—it’s the same technology hospitals use to test blood and urine, and can detect less than a billionth of an ounce of PAHs in a caterpillar.
Tent caterpillars collected from trees around the constructed wetland in early June had PAH concentrations of more than 100 parts per billion. This is several times higher than what science clubbers found in Indian Island clams last fall, suggesting that a lot of street runoff toxics are already being retained by plants in Eastsound—and transferred to insects and to animals that eat insects such as frogs, birds and bats. A 2010 Kwiáht study of the largely agricultural False Bay watershed on San Juan Island found only one-third to one-fifth as much PAHs in aquatic insects.
Science classes at Orcas Middle and High Schools and Orcas Christian School studied recently constructed bioswales this past year, and with the staff of Kwiáht, built and tested scale models of their own design using plants and fungi to capture. The Orcas Island Community Foundation, the San Juan Nature Institute, and People for Puget Sound all contributed to this year’s focus on wetlands and managing runoff.
Kwiáht landscape ecologist Nathan Hodges hopes to attract more local support for more student projects in “green engineering” which he describes as “not just complaining about environmental threats, but building and testing locally meaningful solutions.”
For more information please contact Russel Barsh at RLBarsh@gmail.com or Nathan Hodges at n.hodges@gmail.com
Interested members of the community may write to kwiaht@gmail.com, visit https://www.kwiaht.org or Kwiáht’s Facebook page.
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This study has some interesting possibilities, and would be great if it shows that the constructed wetland is doing its job. I’m a bit concerned, however, because it looks as though the tent caterpillar samples were only collected near the wetland. It is important to include samples collected from other areas where the water is less likely to pick up street run-off. Did you also collect samples from other areas away from roads? If these samples have lower levels of PAH, then your data will support your hypothesis that the wetland is removing PAH. But without a comparison (the control to your experiment), you cannot make any conclusions about how effective the wetland is at removing PAH from road run-off.
Remember that your samples must be collected in exactly the same way, and all of them should be of the same species. Since we have a HUGE population of tent caterpillars this year, collecting the same species from a variety of different locations should be easy!
Barbara: the study you suggest would indeed be very interesting, but it would test a different hypothesis than the one that our students were tackling. Our students were testing whether they could use tent caterpillars to detect PAHs, and their collections and methods were designed to tackle that question. Now that they have demonstrated their method is effective, they can chose to test additional hypotheses using different sampling designs.
Madrona – My concern is with the paragraph that 1) compares the tent caterpillar data with the clam study and the data from False Bay, and 2) the “suggestion” that “a lot of street runoff toxics are already being retained by plants in Eastsound—and transferred to insects and to animals that eat insects such as frogs, birds and bats.” Neither one of these are part of a hypothesis about methods. And neither one is an appropriate comparison to determine if the constructed wetland is doing its job.
Perhaps a better way to include this information would be to say that “the students will be using this preliminary information as part of a study to see if the constructed wetland is removing more of these toxins before street runoff flows into the bay.”
I continue to be delighted that our students are involved in environmental studies, and I would be delighted if they learn appropriate methods and scientific thinking. My concern is about “publishing” conclusions based on…