PEST PROFILES: WASPS

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Nipple Gall Oak Gall Oak Gall Click on image to view larger.

Gall wasps Description: The mealy oak gall wasp asexual generation produces galls that are spherical, 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 later turning beige colored and resembling kernels of wheat. Galls on trees are also caused by other insects, such as certain aphid species, flies, phylloxera, psyllids, thrips, and mites. Damage: Although adult mealy oak gall wasps are rarely seen, high populations can cause noticeable gall formations that will disfigure oak trees. Life cycle: Adult mealy oak gall wasps emerge from galls of the asexual generation during December. All adults are female and do not mate before ovipositing eggs on swollen leaf buds. Eggs hatch in early spring. Larvae develop quickly in leaf tissue and stimulate the development of the galls. Adults of both sexes emerge from these galls after a few weeks. After mating, females oviposit eggs in oak twigs and branches. These eggs remain dormant for 3 to 5 months.