Saturday, August 8, 2015

August 13


There are showy goldenrod plumes everywhere now, and it can’t be too long until the first hints of purple asters appear. In the unmowed periphery fields of Anna Maria, the goldenrod clones are particularly tall and healthy looking.

Now is the time to examine them closely for galls, visible as cancerous looking lumps in the midst of their slender stems. These were formed by the plant itself, in a bit of self trickery induced by a parasite that lives within, the gall fly larva.

When the plants were mere shoots in late spring, the gal fly female laid eggs on its exterior. The newly hatched larva secreted a chemical that caused the plant to develop the gall structure, in which the larva lives within in the soft plant tissue, while the exterior provides a tough protective layer.

In August, as the gall nears its full capacity, the larva too have grown within, spending a portion of the month chewing away a tunnel just to the surface (but not through) of the gall. Then, it settles down to ready for over-wintering, using the gall as a sheltered home.

In early spring, the larva transforms into the adult gall fly, piercing through the thin remaining layer of the gall shell and beginning the cycle anew when the first goldenrod shoots arrive.

Look closely at the galls now; many will have drill holes pierced into them, made by birds like the downy, who have learned to seek out the larva within.

No comments:

Post a Comment