COLORADO POTATO BEETLE, a chrysomelid beetle (Leptinotarsa decemlineata, Say), native to the western United States. This leaf-beetle, first named and described by Say in 1824, fed originally on a wild solanaceous plant, Solanurn rostra tum, abounding in the Rocky Mountain region. With the westward advance of civilization, the cultivation of potatoes was brought to its neighbourhood, and the insect at once took to the cultivated plant and began an eastward spread. By 1864 or 1865 it had crossed the Mississippi river in Illinois. By 1869 it reached Ohio. In 1874 it reached the Atlantic seaboard. In its spread across the country, it flourished best in what is known as the Upper Austral life zone. It did not readily accommodate itself to the severe winters of the far north nor to the hot summers of the far south. As it progressed, certain predatory insects and certain birds be came accustomed to it, and as early as 1869 Paris green began to be used against it ; so that by the time the beetle reached the Atlantic, potato growers in the mid-west were able to control it in their fields.
Great alarm was expressed in Europe. The German Govern ment, early in 1875, issued a decree against the importation of American potatoes, and was followed the same year by Belgium, Spain, France, Russia, Italy, Hungary and Austria, and by Portu gal and Sweden the following year. In spite of the German decree, the beetle was discovered in a potato field near Hamburg, but was exterminated by radical measures. It is quite likely that the insect has been imported by accident into European countries since that date, but in no case has it been established except that shortly after the World War it was found to have been introduced near Bordeaux in France in a region where there had been large bodies of American troops. From that region it has since spread, rather slowly, into surrounding departments, but the French Government, having adopted American methods, feels that it can well be kept in check.
Both the adult beetles and the larvae feed upon the foliage of the potato plant. In the early days it not only caused the loss of entire crops but sometimes destroyed the potato yield of whole counties and of large portions of some States. It materially af fected the market price of potatoes. The extensive work of the insect on the foliage affected the quality of the tuber, and at one time it was difficult to obtain potatoes that were not watery when cooked. The adult beetles pass the winter underground, and in the spring lay their eggs upon the plants. There are two genera tions each year, the leaf-feeding larva descending to the ground to turn to pupa. The insect feeds on nearly all solanaceous plants, including eggplant, tomato and tobacco among the cultivated species. The tender-leaved varieties of potato are most affected.
The insect is held in check by the application of arsenicals. In the United States one formula is, one part Paris green to io to 20 parts of flour, sifted land plaster or fresh air-slaked lime. An other is, I lb. Paris green to 75 to 125 gal. of water, i lb. of quicklime being added to prevent scorching of the foliage by the arsenical. (L. O. H.)