Observations on Shade Tree Insects

Abstract

There has been widespread insect injury to shade trees the past season in the northeastern United States. Three introduced pests—the elm leaf beetle, (Galerucella xanthomelaena), the Japanese beetle (Popillia japonica) and the Europead willow leaf beetle (Plagiodera versicolora)—have defoliated an estimated one ann three quarter million trees. The larch case bearer (Coleophora laricella), seriously injured a quarter of a million larches growing as ornamentals; while the native fall webworm (Hyphantria textor) and the bagworm (Thyridopteryx ephemeraeformis) have seriously damaged an estimated quarter of a million trees each. In addition, the native walnut caterpillar (Datana integerrima) has been very injurious. The total seriously affected is estimated at two and a half million trees, many being well grown, handsome additions to lawns, streets or parkways. Not a few are highly prized for sentimental reasons. These trees may easily be worth an average of $100 each, the total value therefore being $250,000,000. Repeated annual defoliations mean serious lowering of vitality, and if continued for several years a condition obtaining in many sections, the beauty and utility of the trees are destroyed. The probabilities indicate more sweeping damage in 1932. Sickly, dying trees may be a liability rather than an asset. The time is approaching and has come in certain localities, when it will be necessary to provide systematic protection for shade trees, if we would avoid extensive and irreparable losses. The weakening of trees by several abnormally dry seasons and the general loss of foliage described above has produced ideal conditions for serious damage by borers, especially the hickory bark beetle (Scolytus quadrispinosus), the two-lined chestnut borer (Agrilus bilineatus) and the bronze birch borer (Agritus anxius). This has already commenced and more severe damage may be expected in the next season or two. It is by all means advisable to make comprehensive plans for spraying in areas where these various insects were numerous last year. This alone is not sufficient, since the weakened trees need feeding. Otherwise they may succumb to attack by various borers.