Pemphigus spirothecae

Galls on Lombardy poplar (Populus nigra var italica) formed by both twisting and swelling of the petiole

This aphid produces galls in early spring on the petioles of Lombardy poplars and has long been known to occur on poplars in Europe (Connold 1901; Theobald 1929; Stroyan, pers. comm.). No previous record of this aphid exists in North America. The feeding activity of the stem mother causes the petiole to twist into a spiral. The spiralling continues until the stem mother is completely surrounded by petiole tissue (Fig. 1). Within this spiral the stem mother reproduces and the gall swells, producing a large cavity in which the aphid progeny develop. Unlike P. bursarius galls which mature in early summer, galls of P. spirothecae mature in late August and early September. This is primarily attributable to the monoecious life cycle of P. spirothecae which produces one migrant form, the sexupara, within the mature gall. This form corresponds to that of P. bursarius produced on the roots of alternate hosts.

As galls of P. spirothecae mature they change from green to pale red and a variable number of tiny pores appear along the seams (Fig. 3). Much larger openings may develop on this region of the gall, facilitating mass release. At leaf-fall, large numbers of apterae and alates are still found within the galls. Galls of P. spirothecae aphids were extremely abundant on Lombardy poplars in regions surveyed.

- EH Alleyne, FO Morrison: (1977) Some Canadian poplar aphid galls^©