Andricus pedicellatus

Kinsey, 1922

hair stalk gall wasp

Andricus pedicellatus, commonly known as the hair stalk gall wasp, is a cynipid that induces distinctive long, spindly leaf galls on blue oaks (Quercus douglasii). The is fairly common along the Pacific coast of North America. Like other members of the Andricus, it exhibits high specificity, attacking only one or a few closely related oak species.

Hair Stalk Gall Wasp imported from iNaturalist photo 14939182 on 24 October 2023 by (c) Ken-ichi Ueda, some rights reserved (CC BY). Used under a CC BY 4.0 license.

Pronunciation

How to pronounce Andricus pedicellatus: //ænˈdraɪ.kəs ˌped.ɪˈsɛl.ə.təs//

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Identification

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 by their slender, stalk-like form rather than the rounded, bullet-like, or clustered galls produced by such as A. dimorphus or A. pattoni. Close examination of gall on the leaf is sufficient for field identification.

Images

Appearance

The is tiny, typical of cynipid gall wasps. The 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.

Habitat

Found in oak woodlands and savannas where blue oaks (Quercus douglasii) occur. The 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 trees in these open to semi-open oak-dominated landscapes.

Distribution

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

Host Associations

Quercus douglasii - gall blue oak; produces long spindly leaf galls

Ecological Role

As a gall-inducer, the manipulates 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 or broader processes have not been quantified.

Similar Taxa

Andricus dimorphusAlso an Andricus 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 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

More Details

Gall formation mechanism

As with other cynipid , the female lays in leaf tissue using her ovipositor. The developing larva secretes plant growth-like that redirect plant development, causing the formation of the specialized gall structure in which the larva lives and feeds. The wasp eventually chews its way out of the mature gall.