POTATO INSECTS. The principal enemy of the common field potato (Solanum tubcrosum) of the United States is the famous 'potato bug.' or more exactly. the Colorado potato beetle (Doro phora dceemlincata). This insect, originally con fined to the- Rocky Mountain region, where it fed upon the sand-bur (.8o/anum rostratum), readily attacked cultivated potatoes as soon as civilization advanced to its native region. In 1859 it had spread eastward and reached a point 100 miles west of Omaha: in 1801 it invaded Iowa ; in 1864 and 1865 it crossed the Missis sippi, reaching Illi nois both from northern Missouri and Iowa ; in 1867 it had crossed Illinois into western Indiana, and in 1869 had spread across the State and had made its way into Ohio, appearing almost shnultaneously in the northern and south western portions; in July. 1870, it invaded the Province of Ontario; in 1872 it reached western New York, and spread into Pennsylvania. and in 1873 had reached eastern New York and the Dis trict of Columbia: in 1874 the Atlantic Seaboard was gained at several points in Connecticut. New Jersey, New York, Pennsylvania, Delaware, Maryland, and Virginia. Its southern spread was much more slow than in the North, and in 1871 it had not touched the extreme southern counties of Missouri. In fact. it \Va.- not until 1897 that it succeeded in establishing itself in portions of Mississippi and Georgia. Although accidentally introduced into Europe on several occasions. the species has not established itself outside of North America. The female beetles, which have overwintered beneath the surface of the ground or under any shelter, lay their eggs upon young potato plants as soon as they appear above ground, and will even work into the ground to feed upon the young leaves before these have fairly shown themselves. The dark-reddish larva hatch in less than a week, and reach full growth in from two to three weeks, after which they enter the earth to pupate, becoming beetles about a month after the time of hatching. There are
three or four generations each year. This insect is readily controlled by the application of Paris green or some other arsenical poison. either as a spray or dusted dry upon the plants. The po tato bug is also destroyed by the potato-bug enemy (Lcbia grandis). See Colored Plate of INSECTS.
The potato crop is sometimes damaged by the so-called stalk-borer (Go•tyna. ni1cla), an owlet moth which lays its eggs on the stalks not only of potato, but also of tomato and of certain orna mental plants. The larva bores into the stalk and causes the plant to wilt. The potato-stalk weevil (Trichobaris trinotatus) is very common in the Mississippi Valley. The bluish or ash gray beetle deposits a single egg in a slit which she has made with her beak in the stalk of the potato. The larva bores into the heart of the stalk and proceeds downward toward the root, pupating within the stalk. issuing as an adult about the last of August. In both cases all wilt ing vines should be pulled and burned.
The tomato worm (Sphinx ;5-maculate) also feeds occasionally upon potato, but is not an im• portant enemy of this crop. Potatoes suffer, however, sometimes severely, from the attacks of blister beetles. and a leaf-beetle called the three lined potato beetle (Loma trilineata) occasion ally damages the leaves. The cucumber flea beetle (1Ialtica eueumeris) also preys upon the leaves, as does one of the tortoise beetles.
Consult : Riley, Potato Pests (New York, 1876) ; Smith, Manual of Economic Entomology (Philadelphia. 1896).