The lettuce root aphid, Pemphigus bursarius L., can cause considerable damage to crops of summer head lettuce. Its primary host is the Lombardy poplar, Populus italica var. nigra. The aphids, or “stem mothers,” which hatch in the spring from eggs that have overwintered on the poplar, cause hollow, flask-shaped galls to develop on the leaf petioles (fig. 1). The stem mother becomes enclosed within the gall, where it matures and gives rise to between 100 and 250 young.

Photographs were taken by Max Clover, Principal Photographer, and the graph was made by John V. Chambers, Extension Educational Media Specialist, and William Johnson, Senior Artist, U. C., Riverside.