A cynipid wasp, (Hymenoptera: Cynipidae), gall on oak. Photo by Drees.
Common Name: Cynipid wasp
Scientific Name: Varies
Order: Hymenoptera
Description: Two kinds of galls are produced by this wasp. The most notable are produced by the asexual generation that are spherical, corky, 1/8 to 1 inch in diameter and appear on twigs and branches of live oak in late summer and early fall. When first formed, they are pink to pinkish brown and the yellow-green tissue inside is moist and soft.
A number of cynipid wasps cause unique galls on oak trees: the gouty oak and horned oak gall (woody twig galls), Callirhytis spp.; hedgehog gall, Acraspis erinacei Beutenmuller (leaf galls with orange-colored “hair”); wool sower gall, Callirhytis seminator Harris (stick, spongy galls on twigs with seed-like structures inside); woolly leaf gall, Andricus laniger Ashmead (leaf galls on post oak); and, oak apple, Amphibolips spp. (spherical, spongy-filled galls on red oak). Galls on trees are also caused by other insects such as some species of aphids, flies, phylloxera, psyllids, thrips and mites.
Life Cycle: Adults emerge from galls of the “asexual generation” during December. All adults are female and do not mate before laying eggs on swollen leaf buds. Eggs hatch in early spring as leaf buds begin to open. Larvae develop quickly in leaf tissue and stimulate the development of small, beige-colored galls resembling kernels of wheat. Adults of both sexes emerge from these galls or the “sexual generation” after a few weeks. After mating, females lay eggs in post oak twigs and branches. These eggs remain dormant for 3 to 5 months. Then they hatch and stimulate the formation of galls of the asexual generation.
Habitat, Food Source(s), Damage: Mouthparts are for chewing. This cynipid wasp species only affects post oak trees. Adults can be reared from galls pruned from trees and placed in plastic bags when larval development is completed.
Pest Status: Although adult wasps are rarely seen, the galls produced on live oak trees around developing stages are noticeable when numerous and can disfigure trees; medically harmless.
For additional information, contact your local Texas A&M AgriLife Extension Service agent or search for other state Extension offices.
Literature: Drees 1994; Frankie et al. 1978. Johnson & Lyon 1989.