The Encyclopedia Americana (1920)/Elm-Insects

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ELM-INSECTS. Few ornamental trees are more subject to the attacks of insects than are the elms, and especially the American elm. The European species are, however, attractive to the European insects, of which many have been brought over unintentionally, and have spread remarkably because of the absence of their enemies. One of the most notable is the plant-louse known as Colopha ulmicola, which produces the cockscomb galls upon the foliage. It is rarely very troublesome, and has usually done its damage before it can be attacked. Kerosene emulsion, if applied in time, will prove effective. (See Insecticide). A borer (Saperda tridentata) is sometimes troublesome, but there seems to be no satisfactory way to control it, though it has been suggested that the trunk should he washed with lime or soft soap during June and July. Most of the other insects that attack the elms are beetles, their larvæ, or the caterpillars of various moths. These all bite their food, and hence may be attacked with arsenites or other stomach poisons sprayed upon the foliage. Among these insects are the four-horned sphinx-moth (Ceratomia amyntor or quadricornis), a green caterpillar with four little horns near the head and the long anal horn characteristic of the sphinx-moth. The bag-worm (Thyridopteryx ephemeræformis), the gypsy-moth (Ocneria dispar), the tussock-moth (Notolophus or Orgyria leucostigma), and several other general feeders are frequently troublesome. But the most important leaf-eating enemy of the elm is the elm-leaf beetle (Galeruca xanthomelæna), a reddish-yellow, two-striped European insect which appears and eats the leaves in spring. The bottle-shaped yellow eggs are laid in rows on the under sides of the leaves, and the hairy, black-spotted, yellow larvæ eat circular holes between the leaf-veins. Spraying with arsenites is effective, but where more than one brood is produced the sprayings must be repeated frequently throughout the summer. Consult Marlatt, ‘Elm Leaf Beetle,’ Circular 8, Division of Entomology, United States Department of Agriculture (Washington 1895).