An online resource based on the award-winning nature guide

Blackberry Knot Gall

12-28-10      Blackberry Knot Gall

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Winter is a good time to look for galls (abnormal plant growths caused by different agents, including insects, fungi, mites and bacteria) such as the blackberry knot gall, which is much more noticeable when there are no leaves to hide it. Whereas many galls are inhabited by a solitary insect, the blackberry knot gall contains many individual chambers, each containing the larva of the tiny wasp Diastrophus nebulosus. During the spring and summer months, this little wasp deposits eggs into the ridged stems of blackberry which stimulates the plant’s tissue into abnormal growth along the stem. This particular colonial gall can be six inches in length, although two or three inches is more typical (the more eggs that are laid, the larger the gall).  The eggs hatch and the larvae overwinter inside the gall. Adult wasps emerge in the spring and chew their way out of the gall, leaving tiny holes along the gall’s lumpy ridges. In the first photograph you can see where a hungry predator has worked its way into two of the larval chambers.  In the second, multiple chambers and larvae are exposed (sacrificed for the sake of knowledge, but popular food for chickadees on a very cold morning).

 

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