Thecabius affinis (Kaltenbach)

Galls occur on Populus spp., in May-June, mainly on P. nigra and its varieties, and are formed by folding of young leaves in half along mid-ribs; the outer, upper side of the leaf becomes blistered and yellowish or reddish (see influentialpoints.com/Gallery). These are secondary galls containing only the alatiform progeny of the fundatrix, which inhabits a small gall of its own formed by folding the edge of a leaf (fig. 131I).

T. affinis occurs on a wide range of Populus spp. throughout Europe and across Asia to east Siberia, Japan and Korea, and also in North America (see below).

COI barcode sequences have confirmed that T. affinis is present in North America (Skvarla et al. 2017). DNA data have also confirmed the existence of a separate North American species, Thecabius populiconduplifolius (Cowen), which has 2n=28 (Harper & Macdonald 1966). T. populiconduplifolius is virtually indistinguishable from T. affinis and has an identical biology, but with native poplars as primary hosts (Palmer 1952).

Pemphigus affinis

Pinkish pod-like gall on Lombardy poplar, diameter .5 inch, aphid, summer.