Pachypsylla

Most easily identified by the distinctive galls formed on hackberry (Celtis) host plants rather than by examination of the insect itself. Gall morphology varies by species: nipple galls on leaf undersides (P. celtidismamma), bud galls (P. celtidisgemma), blister galls (P. celtidisvesicula), and petiole galls (P. venusta). Adults may be found on or near hackberry trees, especially in autumn when seeking overwintering sites. Examination requires magnification due to small size; wing venation and genitalia are used for definitive species identification.

Adults are minute insects, 3.5–4.5 mm in length from head to folded wing tips. Body form resembles tiny cicadas with a broad head, large compound eyes, and short antennae. Coloration varies from light green to greenish-gray or brownish. Wings are held roof-like over the body at rest. Nymphs develop within galls and possess wing pads in later instars; the final instar has spike-like posterior projections used to cut an exit from the gall.

Strictly associated with hackberry trees (Celtis spp.), including common hackberry (Celtis occidentalis) and other Celtis species. Found in natural woodlands, riparian corridors, and urban plantings where hackberry occurs as native or ornamental vegetation. Adults overwinter in protected crevices on tree bark, under loose bark, or in nearby structures.

North America; range corresponds closely with native distribution of hackberry (Celtis) host plants. Found across eastern and central United States, extending westward where hackberry occurs. Individual species may have more restricted ranges within this general distribution.

Adults emerge from galls in late summer and autumn. Overwinter as adults in concealed locations. Become active in spring when hackberry leaves begin unfolding from buds. Egg-laying timed precisely to coincide with leaf emergence; too early or too late reduces offspring survival. Multiple species may have slightly different phenologies corresponding to their specific gall formation requirements.

Nymphs and adults feed on phloem sap of hackberry trees (Celtis spp.) using piercing-sucking mouthparts. Nutrition is supplemented by essential amino acids provided by the intracellular bacterial symbiont Carsonella ruddii housed in specialized bacteriocyte cells.

• Celtis occidentalis - primary host plantcommon hackberry; most frequently cited host
• Celtis - host plant genusmultiple Celtis species utilized by different Pachypsylla species
• Carsonella ruddii - obligate intracellular mutualistγ-Proteobacteria with smallest known cellular genome (160 kb); housed in 16-ploid bacteriocytes; provides essential nutrients to host

Annual univoltine cycle. Eggs laid on hackberry leaves in spring, timed to leaf emergence. Nymphs hatch and induce gall formation through feeding activity; develop through five instars entirely within the protective gall. Galls are plant tissue growths that envelop the nymph, providing shelter and food. Final instar nymphs possess wing pads and posterior spines for cutting exit holes. Adults emerge from galls in late summer, feed briefly, then seek overwintering sites. No pupal stage; hemimetabolous development.

Nymphs are sedentary gall-dwellers. Adults are capable of jumping to escape disturbance. Autumn mass aggregations occur on building exteriors as adults seek overwintering crevices, occasionally becoming nuisance pests. Precise timing of oviposition relative to host plant phenology is critical for reproductive success. Gall induction represents manipulation of host plant development.

Gall-formers that create specialized microhabitats on hackberry foliage. Galls serve as food and shelter for developing nymphs and are exploited by parasitoid wasps including Psyllaephagus spp. (Encyrtidae) and Torymus spp. (Torymidae). The bacterial symbiosis with Carsonella represents a model system for studying genome reduction and lateral gene transfer in host-symbiont relationships. Galls are generally not harmful to host tree health despite their conspicuous appearance.

Occasional nuisance pest when autumn adult aggregations occur on homes and buildings near hackberry trees. No biting, stinging, or disease transmission; no damage to structures. Control rarely warranted; physical removal by hosing with water is sufficient if needed. Galls are unsightly on ornamental hackberries but do not threaten tree health. Subject of scientific interest due to extreme bacterial genome reduction in symbiont.

• BactericeraAnother psyllid genus with similar body form; distinguished by host plant associations (typically Solanaceae or other plants, not hackberry) and lack of gall formation
• PsyllaEuropean psyllid genus with similar morphology; distinguished by geographic distribution and host plants (often fruit trees), different gall or no gall formation
• CacopsyllaPsyllid genus with similar appearance; distinguished by host plants (often pear, apple, or conifers) and different life histories

Adults are sometimes mistaken for biting insects or disease vectors when aggregating on buildings; they are harmless plant-feeders. Galls are often mistaken for fungal growths or disease symptoms; they are insect-induced plant structures. The insects are sometimes confused with aphids; psyllids lack abdominal cornicles and have different wing venation.

• gall-former
• psyllid
• hackberry
• bacterial symbiosis
• Carsonella
• Sternorrhyncha
• plant-parasite interaction

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Encyrtid Holdings | Entomology Research Museum
• Bug Eric: Hackberry Psyllids: A Fixture of Fall
• Bug Eric: Blacklighting Already?
• Bug Eric: It's Always Something....
• Hackberry Petiole Gall Psyllid, Pachypsylla venusta (Osten-Saken)
• The Life Cycle of the Hackberry Gall-Former, Pachypsylla Celtidis-Gemma (Homoptera: Psyllidae)1
• Genome size ofPachypsylla venusta(Hemiptera: Psyllidae) and the ploidy of its bacteriocyte, the symbiotic host cell that harbors intracellular mutualistic bacteria with the smallest cellular genome