Plant galls

Asked August 30, 2016, 5:03 PM EDT

Can someone verify that these are plant galls? I'm pretty sure they are but would like verification. I usually see them on the top of leaves but these are all underneath the leaf which makes me question a bit. Thank you.

Wadena County Minnesota

1 Response

The photo is of the Red Pea Gall, formed (like all galls, the gall is made from plant tissues, induced by the galler) by the oak pea gall wasp Cynips divisa on Quercus robur. This gall is about 5mm diameter, a flattened sphere with a short stalk to the underside of the leaf. This gall is formed by the asexual generation of this wasp (many gall wasps have hideously complicated life histories) and contains one developing larva. In the autumn the larva will pupate inside the gall and an adult female will be formed. This matures in the gall and then bites its way out. It does not need to mate to become fertile, and seeks out oak leaf buds in which to lay its eggs. This induces the formation of another gall, the red wart gall, in the bud. Males and females emerge from these galls in the spring, mate, and eggs are laid in the veins of expanding leaves