Infestation of the Celtis occidentalis L. by the jumping plant-lice Pachypsylla celtidis-mamma Fletcher.
a) A typical gall caused by infestation and feeding by Pachypsylla nymphs showing a hard mass of tissue. A typical gall is approximately 7 to 9 mm in height.
b) A section through a gall showing the different cell layers and the central chamber of the gall where the growing insect resides throughout the summer months.
c) The nymph Pachypsylla celtidis-mamma Fletcher which causes gall formation (the bar equals 0.3 mm).