The gall of the California gall wasp

A different type of apple fit for fall

Hero-Wasp (1)

The California gall wasp | Graphic by SACtoday

Nothing says fall quite like baked apples, warm apple cider, apple pie — honestly, apple anything. But there’s another rotund fruit that you may find to be a common sight in Sacramento around this time of the year: the oak apple.

To be precise, these “fruits” aren’t actually apples at all. They’re known as galls, which are growths induced by various insects, like the California Gall Wasp. The growth occurs when larvae feast on the tree, which releases hormones that cause a rapid expansion of the tree’s tissues. The inedible galls then serve as protection for bugs, food for some daring animals, and habitat for an entire microenvironment.

Typically, gall wasps are associated with just one of the major oak groups (black, white, and intermediate). This is no different for the California Gall Wasp, which is attached to the white valley oak, one of the most prevalent and important trees native to the Sacramento Valley. The female California gall wasps emerge during the fall, laying their eggs in stems or leaves that stimulate the production of galls.

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