Phytomyza
A genus of small, two-winged flies, the larvae of which mine or burrow between the surfaces of the leaves of many plants, both wild and cultivated. Among the latter may be mentioned Turnips, Wallflowers, and Peas; in fact, most low garden plants, and various shrubs and trees, are liable to attack. The species of this genus are numerous, but all are of small size, about 1/5in. in spread of wing, and 1/12in. long. They are not unlike very small house-flies in form, and are usually dark, slaty-black, or ash-coloured, with the head and the legs often paler. The maggots are whitish; they tunnel out a winding gallery, which may not be visible on the upper surface of the leaf. When full-fed, they change, in the leaf, into chestnut, barrel-shaped pupae, deeply ringed, and showing no external sign of the insect's form. The flies emerge in May and June. One of the most destructive and widespread species is P. nigricornis, the larvae of which live in many different plants. See also Holly-leaf Fly. Fortunately, the mines, unless very numerous, do no great harm to the plants in whose leaves they are formed; but the unsightly blotches on choice garden plants may render the destruction of the larvae desirable. This can be accomplished by crushing the mine, and the contained larva or pupa, between the finger and thumb; or the leaves may be picked off, and burned. Owing to the mode of life, external applications are of no avail in reaching the larvae.