Amphibolips quercusjuglans

The galls of Amphibolips quercusjuglans are readily identified by their location on acorns and their distinctive appearance: fleshy, ovoid to plum-shaped growths, often pinkish to reddish in color, that replace or envelop the normal acorn. The wasp itself is small, typical of cynipids, but identification usually relies on gall morphology and host association rather than adult wasp characteristics. Similar acorn galls include those of other Amphibolips species, but A. quercusjuglans galls tend to be larger, fleshier, and more plum-like than the harder, smaller galls of related species.

Found in oak-dominated habitats including deciduous forests, woodlands, savannas, and urban areas where host oak species occur. The wasp requires mature oaks capable of producing acorns.

Eastern and central North America, associated with the range of its host oaks. Records span from the northeastern United States west to the Great Plains and south to the Gulf Coast.

Adult wasps emerge from galls in late summer to fall, coinciding with acorn maturation. Galls become visible on developing acorns through the growing season, maturing by late summer.

• Quercus - gall inductionHost oak species; specific gall formed on acorns/cupules

The life cycle involves alternation of generations, a common trait in Cynipidae. The sexual generation produces the conspicuous plum galls on acorns; adults emerge, mate, and the resulting agamic generation produces a different gall type (often on buds or leaves) or may have a reduced, poorly known form. The exact alternation pattern for this species has not been fully documented.

Females oviposit into developing acorns, triggering the formation of large, fleshy galls that provide shelter and nutrition for the developing larva. The gall growth dramatically alters normal acorn development.

As a gall inducer, the wasp creates habitat for itself and potentially other organisms. The fleshy galls may be consumed by wildlife, though their tannin content may limit palatability. The wasp contributes to the complex community of gall-formers that structure interactions between oaks and their associated fauna.

The galls are conspicuous and often collected out of curiosity. They have minor significance in horticulture, occasionally noticed in landscaping contexts. No economic importance as pest or beneficial species has been documented.

• Amphibolips quercusostensackeniiAlso forms acorn galls, but produces smaller, harder, more irregular galls rather than the large fleshy plum-like galls of A. quercusjuglans
• Amphibolips quercusspongificaForms spongy acorn galls with a different texture and internal structure

• gall wasp
• cynipid
• oak gall
• acorn gall
• plum gall

• BugGuide
• Wikipedia
• iNaturalist taxon
• NCBI Taxonomy