Pachypsylla spp.

Hackberry psyllid damage from a nipplegall maker, Pachypsylla spp. Photo: Whitney Cranshaw, Colorado State University, Bugwood.
Scientific Name: 
Pachypsylla spp.
Common Name: 
Hackberry Psyllid
Growing Degree Days (GDD's): 
148–448 GDD's, Base 50F, March 1st Start Date. (Source: Cornell Cooperative Extension.)
Host Plant(s) Common Name (Scientific Name): 
Hackberry (Celtis spp.)
Insect Description: 

There are at least 10 species of psyllid in the genus Pachypsylla that are reported on hackberry. Three common species are known as the hackberry blister gall maker (Pachypsylla celtidisvesicula; galls are 3-4 mm wide and blister-like on the leaves and only slightly raised), the hackberry nipple gall maker (Pachypsylla celtidismamma; galls are taller than they are wide and much more raised from the surface of the leaf by comparison), and the hackberry bud gall psyllid (Pachypsylla celtidisgemma; galls begin to form in the bud tissue) (Johnson and Lyon, 1991). Both the hackberry blister gall and the hackberry nipple gall psyllids overwinter as adults in the crevices of rough bark. Occasionally both species will attempt to overwinter inside homes. In both species, there is one generation per year. When new hackberry leaves begin to unfold from the buds, mating and egg laying by these species will occur over the next few weeks. Eggs hatch in approximately 10 days and the nymphs (immatures) will begin to feed on the leaves. Depending on the species, a blister or a nipple gall is formed on the leaf in response to the insect's feeding. Both species will live inside their galls throughout the summer and typically emerge as adults by September. Near large, infested hackberry trees, the adult insects can be a public nuisance when they emerge in large numbers. Adult psyllids are approximately 4-5 mm. long and resemble miniature cicadas. They are also capable of jumping from a resting position and taking flight, and as such are sometimes referred to as jumping plant lice. Hackberry bud gall psyllids are present as adults in the last 2-3 weeks of June. Eggs are laid on leaves and nymphs crawl to newly formed buds to begin gall formation. These nymphs molt into the fifth instar by the fall and remain in that life stage over the winter. Hackberry psyllids use piercing-sucking mouthparts to feed on their host.

Damage to Host: 

Galls may be found on the foliage and twigs of hackberry (Celtis spp.). All are primarily an aesthetic pest, but can be very noticeable. Each of the psyllids discussed here do not typically cause damage that warrants management, as the overall health of the host is not often impacted. Some of the adults may be a biting nuisance in September, however they do not feed on humans, they cannot sting, and will not attack or infest pets. 

Monitoring: 

Search for galls on the leaves of hackberry. Some may be blister shaped and not very raised from the surface of the leaf. Others may be rounded and raised from the leaf surface taller than they are wide. Note that there are also species of gall midges that create galls on hackberry (ex. Celticesis spiniformis). 

Cultural Management: 

Remove and destroy leaves with fresh galls before adult emergence. 

Natural Enemies & Biological Control: 

Parasitic wasps are noted as important natural enemies of hackberry psyllids. A parasitoid wasp (Psyllaephagus pachypsyllae) is able to parasitize approximately 30% of the hackberry bud gall nymphs. On hackberry nipple gall psyllid, 47-51% of the nymphs may be killed by Torymus pachypsyllae, Psyllaephagus pachypsyllae, and Eurytoma semivenae, among others. A predatory weevil (Conotrachelus buchanani) has also been associated with hackberry psyllids (Johnson and Lyon, 1991).

Chemical Management: 

Acetamiprid (L)

Azadirachtin (NL)

Beauveria bassiana (NL)

Carbaryl (L)

Chlorpyrifos (N)

Cyantraniliprole (NL)

Dinotefuran (NL)

Flonicamid+cyclaniliprole (N)

Horticultural oil (eggs) (L)

Imidacloprid (L)

Insecticidal soap (NL)

Isaria (paecilomyces) fumosoroseus (NL)

Neem oil (NL)

Pyrethrins+sulfur (NL)

Tau-fluvalinate (NL)

Notes: 

Active ingredients that may be applied systemically include: Acetamiprid (injection), azadirachtin (injection, soil drench), cyantraniliprole (soil drench, soil injection), dinotefuran (soil drench), imidacloprid (soil drench), and neem oil (soil drench).

When used in nursery settings, chlorpyrifos is for quarantine use only.

Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.

Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.

Read and follow all label instructions for safety and proper use. If this guide contradicts language on the label, follow the most up-to-date instructions on the product label. Always confirm that the site you wish to treat and the pest you wish to manage are on the label before using any pesticide. Read the full disclaimer. Active ingredients labeled "L" indicate some products containing the active ingredient are labeled for landscape uses on trees or shrubs. Active ingredients labeled "N" indicate some products containing the active ingredient are labeled for use in nurseries. Always confirm allowable uses on product labels. This active ingredient list is based on what was registered for use in Massachusetts at the time of publication. This information changes rapidly and may not be up to date. If you are viewing this information from another state, check with your local Extension Service and State Pesticide Program for local uses and regulations. Active ingredient lists were last updated: January 2024. To check current product registrations in Massachusetts, please visit: https://www.mass.gov/pesticide-product-registration .