What is branch washing and how does it relate to the “L2 Survey”? - January 29, 2016

Posted on March 24 2016

By Drew Carleton, Entomologist, Forest Management Branch, Department of Natural Resources (DNR), Government of New Brunswick

If you have been following our scientist’s blog entries, you may have seen the terms “branch washing” and “L2 Survey” and thought to yourself, “What are they talking about?” Branch washing is just as it sounds, a process whereby branches are washed in a special solution to remove the unnoticeable insects that might be hiding on them. This allows us to count the insects and get an idea of the greater population trends. Branch washing is the process used in the “L2 Survey” to determine spruce budworm populations; it’s called this because the second instar larvae are collected from the branches that are washed. Instar is just a fancy word for stage.

Image 1: Life cycle of spruce budworm

Let’s take a tour through the process: It all begins on the highways and back roads of New Brunswick where you might see a team of DNR staff setting up shop on the side of Route 7 or on the dirt road leading to your favorite fishing pond. Branches are sampled at a network of plots within the province. Each plot provides an estimate of the insect populations in that area. A two person crew use pole pruners to cut branch samples from the mid-canopy of spruce or balsam fir trees (see  image below) The pole pruners allow us to reach up to 20m into the canopy of mature trees where the budworm are living.    

Image 2: Pole pruning

Once branches have been cut (three per plot), we record information on tree species, location, amount of defoliation and branch size then bag them individually so that they can be sent to our facilities in Fredericton to be processed. Upon arrival, branches are assigned to a wash-cycle, whereby the branch is cut into small sections, placed into a large bucket with a solution designed to break down the webbing that each larvae uses to protect itself during the winter. The shelter they create to survive the winter is called a hibernaculum.  The branches then remain in the bucket for two hours, and are stirred occasionally before the contents are sieved and filtered (See images below).

Image 3: Bucket branches being washes

Image 4: Funnel seperater

The result of this process is a sheet of filter paper filled with lichens, mosses, and in some cases small insects like spruce budworm larvae. This filter paper is then handed to our expert staff who are trained at identifying and differentiating insect larvae. They then sift through the content and count the budworm, recording these results (see images below). This process is repeated over 5000 times each year, providing the data necessary to monitor spruce budworm populations.

Image 5: Image of filter paper

Image 6: Someone under microscope

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