Tiny Insects make Galls on Poplars.

Star (Christchurch), Volume XLIV, Issue 191, 13 August 1931, Page 8

Tiny Insects make Galls on Poplars.

Nature Notes.

By James Drummond, F.L.S., F.Z.S. f J'HE STEMS of leaves of poplars sometimes have excrescences about an inch long, and shaped like miniature sacks or balls. On cutting these open. Dr D. Miller, of the Cawthron Institute, found that the walls were thick and tough. In each gall there was a mass of white woolly secretion exuded by female aphides, present in the gall.

This gall-aphis has a somewhat complicated life-cycle. The females lay minute yellowish-white eggs in a crevice in the bark. Young forms hatch out of the eggs, move on to the stems of the leaves, and make the galls, from which winged insects escape in the summer and autumn, to migrate to cruciferous plants, such as cabbages, wild turnips and mustard, a'nd to allied weeds. This insect, commonly known as the poplar-leaf stem-gall, has an official name out of all proportion to its size: Pemphigus populi-transversus. They are only about one-twentieth of an inch long, and a lens is necessary to realise that they are perfect insects, with limbs and organs complete.