The New International Encyclopædia/Elm-Insects
ELM-INSECTS. The elm seems peculiarly susceptible to the attacks of foliage-eating insects. Most of these, however, are foreign species, which have been accidentally imported and acclimated, and which are likely to attack the European elm in preference to American species. Hence it has been recommended that a few European elms be included within all plantations to serve as traps for the insects, which may thus be attacked more easily than if scattered over the whole plantation. The gypsy moth, brown-tail (see Moth, Brown-tailed), tussock-moth (q.v.), and other defoliaters, are more or less numerous, especially in New England, where great sums of money (see Gypsy Moth) have been and continually are spent by local governments in suppression of the evil; while the bagworm and various minor insects, such as bark-lice and leaf-beetles, attack these trees in the South and West.
|a. Adult beetle; b. full-grown larva; c. elm-leaf, with grubs eating and laying eggs; d. eggs (magnified).|
The Elm-Leaf Beetle is, of all these, perhaps the most generally destructive to the foliage of this tree. It is a well-known European pest, which first appeared in the United States about 1837, and has gradually become widespread. It is a yellowish-brown chrysomelid beetle, a quarter of an inch long, with three indistinct dark stripes on the wings. The beetles begin to feed while the leaves are growing, and eat round holes in them. They soon deposit clusters of bottle-shaped orange-colored eggs on the under sides of the leaves, and then die. The caterpillar-like grubs speedily hatch and begin feeding. They are black at first, but become more yellowish with each molt, until finally they are wholly yellow except three dark stripes. South of Philadelphia, two broods are usually produced annually, but northward only one. The larvæ feed voraciously and soon skeletonize the leaves, and the infested tree rapidly becomes as if burned. The grubs then crawl or fall to the ground and go into the pupa state near or on the surface of the soil, sometimes so numerously as to make a noticeable yellow carpet all about the trunk of the tree. Ordinarily, however, they are more scattered, seeking crevices which will protect them somewhat; and in this state those of the single northern brood or of the second southern brood pass the winter, full details of this life-history will be found in Marlatt's Elm Leaf Beetle, published as “Circular No. 8” by the Department of Agriculture (Washington, 1895), and the author recommends the following remedial measures: “The adults, for a week or two after emerging, feed on the newly expanded foliage, and a spraying with Paris green or other arsenical will destroy the great majority of them. Especial pains should be taken to accomplish the destruction of the insect in this stage. . . . If rains interfere with spraying for the adults, or if it be neglected, the trees should be sprayed with arsenicals promptly on the first appearance of the larvæ, and the application perhaps renewed a week or ten days later, especially if rains have intervened.”