Gagne Description ²

Common, on Eucarya hickories; usually clustered, on lower leaf surface between veins; 2.5-4.5 mm in height, from depressed-spherical with slight peak to onion shaped; with long, thick, brown hair obscuring gall surface; base with circular, deep, central excavation, leaf without exfoliation surrounding connection; larval chamber basal, ovoid, floccose, green to brown, occasionally with slight violet hue, a tuft of brown hairs issuing from apex of larval chamber at end of fibrous bundle that terminates at gall apex; gall wall thick, woody. Galls are superficially similar to those of C. aggregata and C. purpurea because of their dense hair covering. Osten Sacken (1862) described two kinds of galls for this species. One kind is limited here as C. holotricha by the designation of the lectotype that shows a characteristic intrusion of hairs from the gall apex into the larval cavity. The other kind presumably belongs to C. aggregata but none of Osten Sacken's galls of that sort remain. Unlike galls of C. holotricha that are usually discrete and grow between veins, those of C. aggregata appear in closely packed rows along the midrib. It is not always possible to differentiate the more onion-shaped galls of C. holotricha from those of C. purpurea without opening them to see whether there is an apical intrusion of hairs that C. purpurea galls do not have. In addition, the inside surface of the C. purpurea galls is almost always purple instead of green to brown.

Gagne Biology Note ²

In central Maryland, soft, whitish-green galls were first noticed on June 9 and contained first instars. On June 15, galls were nearing full size and contained first instars. By June 17, some galls were hard and contained second instars, as well as young hymenopterous parasitoids. By June 22 and through July 16, all galls were at full size and hard. On August 3, galls contained large second instars. By August 31, more than 2/3 of the galls contained third instars. The full-grown larva is opaque white and practically fills the larval chamber. The exit tunnel is made to one side of the gall.

Sources and Credits

1. (c) Adam Kranz, all rights reserved, uploaded by Adam Kranz
2. (c) Adam Kranz, some rights reserved (CC BY-SA)

More Info

• iNat taxon page
• Animal Diversity Web
• Biodiversity Heritage Library
• BOLD Systems BIN search
• BugGuide
• CUIC Insect Images
• Field/Photo ID for Flies
• Global Biodiversity Information Facility (GBIF)
• Guide to Hickory Midge Galls
• Guide to Hickory Midge Galls
• Maryland Biodiversity Project
• NatureServe Explorer 2.0
• Systema Dipterorum

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