Pemphigus bursarius (Linnaeus, 1758)

Stem mothers form flask-shaped galls on the leaf petiole or occasionally on young shoots (Harper 1966). As many as three or four galls may occur on one leaf, each producing up to 78 alatae (Alleyne and Morrison 1977). First instars of this species include a "soldier" caste distinguished by their aggressive behaviour in attacking natural enemies (Rhoden and Foster 2002). Soldier aphids attack using sustained thrusts of their stylets to pierce the predator's cuticle. Alternatively, soldier aphids may use their legs to squeeze predators to rupture the cuticle and damage internal organs (Rhoden and Foster 2002). Such attacks are costly to the aphids but can kill predaceous maggots (Diptera: Syrphidae) to protect other aphids remaining in the gall.

Populus nigra L. var. italica is the primary host (Harper 1959a; Alleyne and Morrison 1977). Secondary hosts include lettuce, on which P bursarius is considered to be an economically important pest in Europe and in the United States (refs. in Harper 1966; Alleyne and Morrison 1977). Other secondary hosts include carrot (Apiaceae: Daucus sp.), lamb's quarters, and nipplewort Lampsana communis L. and Sonchus spp. (Asteraceae) (Palmer 1952). The aphid apparently has wide distribution in Canada, being previously reported from Alberta, Ontario, and Quebec (Harper 1966).

- Kevin Floate: (2010) Gall-inducing aphids and mites associated with the hybrid complex of cottonwoods, Populus spp. (Salicaceae), on Canada’s grasslands^©