Galls, Diseases, and Pests - Two-horned Gall Wasp
Dryocosmus dubiosus
The Two-horned Gall Wasp females lay their eggs in the leaf veins on the underside of live oak leaves. As the galls grow, they apparently take nutrition from the leaf veins which sometimes causes the leaf tissue past the gall to die off. The "horns" on the gall develop after the eggs have hatched.
Older galls with new galls erupting.
Sometimes the new galls are pink!
Many gall-inducing insects produce more than one generation per year, and due to a number of factors, the galls can be very different from one generation to the next. The Spring generation of the Two-horned Gall Wasp not only looks different, there is a lot of variation in where the galls develop and how they look as they age. The Spring galls can be found both on catkins--the flower clusters--or on the leaves. In this photo, the galls are on the catkins.
Here the galls are spread out on some new leaves.
Here several galls on the leaves have grown together.