Observations : April5, 2006 Time: 9:30 am Weather: Overcast, cool breeze

Galling Behaviour  A walk along the edges of the field near the Information Kiosk shows signs of life, even on this dreary Spring day. Although difficult to recognize without its yellow spray of fall flowers on its top, Canada Goldenrod (Solidago canadensis) will still be standing tall (typically 75-100cm) on its single dead brown stem. You’ll notice that some of the stem sections are swollen in the shape and size of large marbles. These spheres are called galls, a home for the larva of the goldenrod gall fly (Eurosta solidaginis). This fly’s lifecycle begins in late Spring when its mother injects the goldenrod stem with an egg. Upon hatching, the fly larva begins eating the inside of the goldenrod while secreting a chemical that causes the plant stem to experience irregular growth. The bulge called a gall, will be the larva’s home, usually until Spring of the next year. The cool fall temperatures prompt the larva to dig a tiny escape tunnel up to, but not through the “skin” of the gall. The tunnel is created at this time because the larva will eventually transform into an adult within the gall and adults have no mouth with which it can chew. How can a tiny grub (approx 0.5 cm long) make it through our cold winters? Using sugars gained by eating the goldenrods innards, the larva makes a chemical called glycerol that doesn’t allow critical body parts to freeze. In the spring, the lifecycle continues and finally turns into a winged adult. The adult will crawl to the end of the escape tunnel where it will wedge itself against the walls and pump body fluids into a part of its head. This “hydraulic jack” will then burst its way through the thin outer tissue of the gall. Downy woodpeckers and black-capped chickadees are the biggest predators of the larva, especially those galls located close to the woodland edges. Downys will tap the gall, listening for the site of the escape tunnel and dig in through that to retrieve their food.

The Naturalist's Notebook is a regular publication. If you have any questions or topics that you would like to see addressed, please call John Gilbert, Manager, Fish and Wildlife, J.D. Irving, Limited, (506) 632-7777 or email honeyman.kelly@jdirving.com