Hackberry Gall Psyllid

Hackberry gall psyllid, Pachypsylla spp.

Hackberry gall psyllids, also known as hackberry nipplegall makers, hackberry blister gall psyllid, and jumping plant lice, are a 4-5 mm insect seen in autumn near hackberry trees. When the adults exit the galls during autumn, they search leaf litter, bark, and other crevices for a place to overwinter. In spring, they emerge to lay eggs on the new hackberry leaves. The nymphs feed on the leaves and cause the characteristic nipplegall for which the psyllids get one of their common names.

Hackberry gall psyllids often conjugate on window screens.

When the weather is warm, the adult psyllids swarm to houses, particularly on screens of windows and doors. Although a nuisance, they are not harmful to people, pets, or property. Control is difficult and not always recommended. Some parasitic wasps including Torymus pachpsyllae, Psyllaephagus pachypsyllae, and Eurytoma semivenae reportedly kill up to 51% of hackberry gall psyllids. As the wasps overwinter in galls on hackberry, it is not recommended to destroy the leaves of the tree. It should also be known that while hackberry gall psyllids can be numerous, the galls do not kill the host plant.