Pemphigus
A genus of Aphides, distinguished from the more frequently observed forms by the six-jointed, short antennae, the absence of honey tubes near the end of the body, and the front wings having all the veins that end on the hind margin unbranched. The body is generally more or less bedecked with a woolly secretion, especially near the tip. Several species are found in Britain. Of these, some form galls on Elms, and on Poplars (e.g., P. bursarius on leafstalks of the Black Poplar), while most of them feed on the roots of plants, especially of Compositae and of grasses. The latter species may be found in small companies, in cavities, loosely lined with the white secretion. The insects prefer light, sandy soils. P. lactucarius and P. fuscifrons both injure garden Lettuces considerably at times. See Lettuce. M. Lichtenstein, of Montpellier, has brought forward strong arguments in support of the belief that the gall-makers pass through a cycle, in which a generation of gall-makers on trees alternates with one feeding on the roots of herbaceous plants; and he has proved that this occurs with the allied Tetraneura Ulmi, the maker of the erect galls (about the size of small Cherry-stones), common on Elm leaves in various English localities. This species of Aphis he has traced from the Elm galls to roots of Maize, and of Cynodon dactylon, and vice versa.