Andricus pedicellatus

The hair stalk galls of A. pedicellatus are diagnostic—no other cynipid on blue oaks produces such elongated, spindly leaf galls. The galls can be distinguished from other Andricus species by their slender, stalk-like form rather than the rounded, bullet-like, or clustered galls produced by congeners such as A. dimorphus or A. pattoni. Close examination of gall morphology on the host leaf is sufficient for field identification.

The adult wasp is tiny, typical of cynipid gall wasps. The species is best recognized by the galls it produces: long, slender, hair-like stalks rising from the leaf surface. These spindly galls are distinctive in form and separate this species from other Andricus species that produce more rounded or clustered galls.

Found in oak woodlands and savannas where blue oaks (Quercus douglasii) occur. The species is associated with the Mediterranean-type climate of coastal California and Oregon, characterized by dry summers and moist winters. Galls develop on the leaves of host trees in these open to semi-open oak-dominated landscapes.

Pacific coast of North America, specifically California and Oregon, where blue oaks are native. The distribution corresponds to that of its primary host, Quercus douglasii.

• Quercus douglasii - gall hostblue oak; produces long spindly leaf galls

As a gall-inducer, the wasp manipulates host plant tissue to create a protected feeding and development chamber. The galls represent a form of plant-animal interaction where the insect directs host plant growth through chemical secretions. The ecological impacts of this interaction on individual tree fitness or broader ecosystem processes have not been quantified.

• Andricus dimorphusAlso an Andricus species on oaks, but produces clustered midrib galls on chinquapin oak (Quercus muhlenbergii), not the long spindly stalk galls on blue oak
• Andricus pattoniProduces galls on post oak (Quercus stellata) leaves; gall morphology differs from the hair stalk form of A. pedicellatus
• Disholcaspis quercusglobulusA cynipid gall wasp, but produces round, detachable twig galls on white oak (Quercus alba) rather than leaf galls

• cynipidae
• gall wasp
• oak gall
• blue oak
• quercus douglasii
• leaf gall
• pacific coast

• BugGuide
• Wikipedia
• NCBI Taxonomy
• Gall darn it! Gall insects on hickory, oak, and elm, Phylloxera caryaecaulis, Andricus palustris, Colopha ulmicola — Bug of the Week
• Cynipidae | Beetles In The Bush
• The Insects Behind the Weird Growths on Plants
• Ted C. MacRae | Beetles In The Bush | Page 8
• galls | Beetles In The Bush