Pemphigus knowltoni Stroyan

Galls are green, pouch-like, of variable shape, on undersides of leaves of Populus angustifolia alongside the mid-rib at the base of the lamina (Stroyan 1970). Fundatrix and immatures in gall are blackish green. Alatae (BL 1.8-2.1 mm) are mature in the gall in July, and migrate to an unknown secondary host. Described from Utah, USA.

Pemphigus knowltoni sp. n.

Biology: Pemphigus knowltoni causes variably shaped pouch galls on the underside of the leaves of Populus angustifolia, typically alongside the mid-rib at the base of the lamina. The galls collected in the type locality were green in colour. The progeny of the fundatrix are all alate, and contain rostrate, i.e. exultype, embryones. From this it appears that the species is heteroecious, but the secondary host is unknown.

P. knowltoni lies closest morphologically to P. populitransversus Riley, to which it will key if referred to Palmer (1952). P. populitransversus causes petiolar galls on the broad-leaved Populus sargentii and P. deltoides (see “Biology” above). It is quite possible that P. knowltoni is the primary host form of an already described Pemphigus from roots of a secondary host, but it seems desirable to describe it pending opportunities for further investigation of its biology.

Distribution and type material The type material consists of the contents of three galls collected from Populus angustifolia at Garden City, Utah, 7.vii. 1966 (G. F. Knowlton and H.L.G.S.). The holotype is an alate migrans from this collection, and the paratypes three fundatrices and 23 alate migrants with the same data. No other collections of the species are at present known to me. The species is named for Professor George F. Knowlton of Logan, Utah, in recognition of his kindness in showing me the aphid fauna of Utah during two visits paid to Logan in 1964 and 1966.