Friday, September 24, 2010

Oak Bullet Gall


As I walked by the pin oak trees on the family farm, I almost did a double take. It appeared to have hundreds of thousands of berries on it and though not an expert on all things tree, I did know enough that oaks don't have berries. A closer inspection revealed tiny round wood cysts which after research are named oak bullet gall. This is my first encounter with them.

A wasp called a cynipid lays an egg on the leaf which hatches out a larvae. The larvae then injects the leaf with DNA alternating substances that cause the tree leaf to form a protective gall around the larvae protecting it from the elements while providing nourishment to it. Then in the fall, the wasps chews out of the gall and flies over to the terminal bud and lays another egg. The larvae hatches in the spring and another gall is formed which another wasp eventually chews its way out.

This brief paragraph is what I have obtained from reading a couple dozen websites on the subject but still I have questions. If the first gall on the leaf is to hatch a wasp to lay an egg on the terminal bud which then forms a gall and hatches another wasp, what does this wasp do? Why not directly lay the egg on the terminal bud? The only answer I seem to find is that most sites agree that there is much confusion on the life cycle of the cynipid that forms these galls.

Anyone know more?

5 comments:

Ron said...

All I knew about them was that a wasp caused them to form them the way you described. Those galls range between about 1" to 1 1/2" around here. I find them all over on the ground.

Ron

R. Sherman said...

My parents used to have their oaks filled with those things. Really amazing adaption.

Cheers.

sage said...

THanks for the information--I'd seen them but didn't know what caused them.

Ed said...

Ron - I'm not sure I would want to be around a tree full of 1.5" galls starting to hatch. Might be the same result as sleeping by your pumpkin growing on the manure pile.

R. Sherman - I thought it was fascinating too.

Sage - Who says blogging can't be a learning experience!

TC said...

So, does it harm the tree?