Psylla
A large genus of small insects, nearly related to Aphides, which they resemble in their general appearance. They feed on the leaves and young branches of plants, sucking the sap through their long beaks. They frequently live in company, and are often more or less covered with a cottony secretion. Some species give rise to distortions of such a kind as to cause them to be reckoned among gall-makers. In repose, the wings are sloped over the back like a penthouse, and the front pair are rounded at the tip. These insects may be known from Aphides by their rather larger size, rounded wings, and harder bodies, and, above all, by their power of leaping, which is given by the strong, thick thighs. They do not show the rapid vegetative reproduction or budding so general among Aphides. The species are found on many different woody plants, and all have very similar habits. Several occur on the Pear-tree (see remarks on INSECTS under Pear), of which P. pyrisuga is probably most hurtful; and P. Mali, at times, does much harm to Apples. They secrete from their bodies a sweet, clammy substance, which is produced at the expense of the fluids of the plants, and falls on and clogs the surfaces of the leaves. This weakens the food-plants considerably. During winter, many of these insects are hidden in the crevices of the bark, or in similar shelters; hence, no such retreat should be permitted to exist in the neighbourhood of valuable trees that suffer from their attacks.
Remedies. Remove all facilities for concealment from the trees and shrubs. It has been recommended to wash the branches and leaves first with a solution of 2oz. soft soap to a gallon of water, and to follow this up with tobacco-water, Gishurst's Compound, or other insecticides, as recommended under Aphides (which see). These may be pumped on to the trees from a garden engine.