NOTE: this guide is still usable but it has been superseded by a more complete version available at:
https://www.gallformers.org/id
all future updates will be made there.
Key to galls formed on Celtis species trees in North America by Cecidomyiid midges and Aphalarid psyllids. Midge info and photos from: THE NORTH AMERICAN GALL MIDGES (DIPTERA: CECIDOMYIIDAE) OF HACKBERRIES (CANNABACEAE: CELTIS SPP.) By Raymond J. Gagné and John C. Moser. Psyllid descriptions from The psyllids of America North of Mexico: (Psyllidae: Homoptera) (Subfamilies Psyllinae and Triozinae)
By Tuthill, L.D. Iowa State College Journal of Science 17: 443-660, 1943; Insects Injurious to Forest and Shade Trees
Alpheus, S.P. 1891. Fifth Report of the United States Entomological Commission; and Insects Injurious to the Hackberry by CV Riley.
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