Andricus brunneus

Distinguished from other Andricus species by the clustered, round, reddish-brown leaf galls on white oaks, particularly blue oaks. The galls are approximately 6 mm in diameter with a single larval chamber each. The exclusive presence of females and Pacific Coast distribution further separate this species from eastern North American congeners.

Adults are brown or reddish-brown, approximately 3 millimetres in length. The galls are round, 6 millimetres in diameter, reddish to light brown in color, and typically occur in clusters on leaf surfaces.

Associated with oak woodlands and savannas where white oaks, especially blue oaks (Quercus douglasii), occur. The species depends on the presence of its specific host oak species for gall formation.

Pacific Coast of North America. Specific range includes California and adjacent regions where blue oaks and other white oaks are present.

Adult females emerge from galls in autumn. Gall formation occurs on developing leaves during the growing season.

• Quercus douglasii - gall formation on leavesPrimary host; blue oak
• white oaks (Quercus section Quercus) - gall formation on leavesBroader host range within white oak group

The life cycle involves egg deposition into developing oak leaf tissue, induction of round galls, larval development within a single chamber per gall, pupation inside the gall, and adult emergence in autumn. Only females are produced, indicating parthenogenetic reproduction without a sexual generation.

Females emerge in autumn and presumably oviposit into oak buds or developing tissues to initiate the next generation. The species has eliminated the male sex entirely.

As a gall-former, the species manipulates oak leaf development to create protected feeding chambers. The galls represent a form of plant-insect interaction that may affect leaf physiology, though specific ecological impacts are not well documented.

No significant direct human impact. The galls are of interest to naturalists and entomologists studying oak gall wasp diversity. No economic damage to oaks has been reported.

• Andricus pattoniAnother Andricus species forming leaf galls on oaks, but produces different gall morphology and occurs in different geographic regions
• Andricus dimorphusForms clustered galls on oak leaves but on different host species and with different gall structure; known as clustered midrib gall wasp

• gall wasp
• oak gall
• parthenogenesis
• Pacific Coast
• Cynipidae
• Quercus
• leaf gall

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