Andricus quercuscalifornicus (occasionally Andricus californicus), or the California gall wasp, is a small wasp species that induces oak apple galls on white oaks, primarily the valley oak (Quercus lobata) but also other species such as Quercus berberidifolia. The California gall wasp is considered an ecosystem engineer, capable of manipulating the growth of galls for their own development. It is found from Washington, Oregon, and California to northern regions of Mexico. Often multiple wasps in different life stages occupy the same gall. The induced galls help establish complex insect communities, promoting the diversification in niche differentiation. Furthermore, the adaptive value of these galls could be attributed their ecological benefits such as nutrition, provision of microenvironment, and enemy avoidance.

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