Hackberry trees are host to a variety of gall-making insects. One of the most noticeable and common species is the hackberry nipple gall, a type of psyllid (SILL id) insect. Nipple galls appear as 1/8 to 1/4 inch swellings of tissue on leaves or petioles. If carefully cut open, inside you may see the pale, developing psyllid inside. Adult psyllids resemble tiny (3/16 inch long) cicadas and can become abundant in the fall. During this time they may enter homes for protection from cold weather, often crawling through window screening. These insects may become a nuisance, but they do not bite and are not harmful.
Hackberry trees also harbor many gall-forming midges (flies in the family Cecidomyiidae), including the thorn gall, Celticecis spiniformis (Patton). Immature stages of these species, when carefully dissected out of galls, appear maggot or grub-like and have no legs or antennae as do psyllid immatures.
Nearly any hackberry tree you find is likely to be infested with at least some kind of gall-forming insect. Some species of gall makers cause galls to form on the leaves and petioles, some on leaves. Few galls are harmful to the tree, however.
Habitat & Hosts
A number of Pachypsylla psyllid species occur on hackberry (Celtis spp.), including the hackberry nipple gall maker (P. celtidismamma (Riley), the hackberry blister gall maker (P. celtidisvesicula Riley), and the hackberry bud gall maker (P. celtidisgemma Riley).
Common leaf gall-forming species overwinter in the adult stage in bark cracks and crevices. Adults mate in the spring and females lay eggs on the underside of expanding leaves. Nymphs hatch from eggs in about 10 days and begin feeding, causing leaf tissue to expand rapidly into a pouch or gall around the insect. Nymphs develop through several stages (instars) before emerging as adults in the fall (September), although the hackberry bud gall maker overwinters inside the gall as a last stage (5th instar) nymph to emerge as adults in early summer. One generation occurs annually.
ManagementIf you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.
Little can be done with insecticides to control gall-making insects. Keeping windows closed and well sealed will keep most insects out. If adult hackberry nipplegall makers become a nuisance pest year after year, tree removal may be the best option.