There are ten distinct species of insects preying upon the potato-plant within the limits of the United States. Many of these ten species are confined within certain geographical limits. Their habits and history differ very widely. Some attack the potato both in the larva state and in the perfect or winged state; others in the perfect or winged state alone; and others again in the larva state alone. In the case of seven of these insects, there is but one single brood every year; while of the remaining three there are every year from two to three broods, each of them generated by females belonging to preceding broods. Eight of the ten feed externally on the leaves and tender stems of the potato; while two of them burrow, like a borer, exclusively in the larger stalks. Each of these ten species has its peculiar insect enemies; and a mode of attack which will prove very successful against some of them will often turn out to be worthless when employed against the remainder. [Illustration] ~The Stalk-Borer~,[A] (_Gortyna nitela_, Guenee.)--This larva (Fig. 2,) commonly burrows in the large stalks of the potato. It occurs also in the stalks of the tomato, in those of the dahlia and aster, and other garden flowers. It is sometimes found boring through the cob of growing Indian corn. It is particularly partial to the stem of the common cocklebur, (_Zanthium sirumarium_;) and if it would only confine itself to such noxious weeds, it might be considered more of a friend than an enemy. It is yearly becoming more numerous and more destructive. It is found over a great extent of country; and is particularly numerous in the valley of the Mississippi north of the Ohio River. The larva of the stalk-borer moth leaves the stalk in which it burrowed about the latter part of July, and descends a little below the surface of the earth, where in about three days it changes into the pupa, or chrysalis state. [Footnote A: Where no hair-lines are given, the insects are represented life-size.] The winged insect (Fig. 1,) which belongs to the same extensive group of moths (_Noctua_ family, or owlet moths) to which all the cut-worm moths appertain, emerges from under ground from the end of August to the middle of September. Hence it is evident that some few, at all events, of the female moths must live through the winter, in obscure places, to lay eggs upon the plants they infest the following spring; for otherwise, as there is no young potato, or other plants, for them to lay eggs upon in the autumn, the whole breed would die out in a single year. This insect, in sections where it is numerous, does more injury to the potato crop than is generally supposed. ~The Potato-Stalk Weevil,~ (_Baridius trinotatus_, Say.)--This insect is more particularly a southern species, occurring abundantly in the Middle States, and in the southern parts of Missouri, Illinois, and Indiana. It appears to be totally unknown in New-England.