Hairy Gall Wasp

Canyon live oaks (Quercus chrysolepis) are plentiful on Spring Hill (a “satellite” volcanic cone) at the base of Mount Shasta (Shasta County CA). When young, the evergreen, leathery leaves have spiny margins while older leaves are usually entire. Both leaf forms may be found on the same tree.

Andricus lasius, a cynipid wasp, has induced galls on many of the Spring Hill canyon live oaks. These galls form along the midrib vein on the underside of live canyon oak leaves. Round, hairy and a greyish beige in color, hairy oak galls can detach from the leaf, that is, they are not an integral part of the leaf.  Polythalamous (two or more larvae in separate chambers), hairy oak galls may contain up to six larval chambers.

Between January and March the adult A lasius females emerge from the gall. The adults live for about a week and do not feed. Before dying the females lay eggs on canyon live oak leaves. Once the eggs hatch the larvae begin to release substances that are responsible for the gall growth. Cynipid wasps commence feeding on the liquids in the layer of cells forming the chamber walls and continue to stimulate cell growth within the gall. The strong chewing mouth parts of cynipid wasp larvae break open the cell walls and the larvae can then suck up the nutritive cell liquids. In addition, cynipid wasps can convert plant starch to sugars through enzymatic action. The larvae have intestines which are closed for most of their larval stage. Just before pupation, the intestine opens and emits wastes, which it is assumed the gall tissues absorb, because wastes are not found in the galls. The pupal stage of the life cycle occurs within the gall. Adults gnaw their way out of the galls, often waiting just below the gall surface until climactic conditions are acceptable before breaking out of the gall completely.

A lasius wasps are specific to canyon live oaks.

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