Potato Bug, a term popularly used to designate any insect that affects the potato injuriously. There are more than a dozen such insects in the United States; but in view of its interesting history and of its being incomparably the most serious and destructive enemy of that plant, the term has come to be applied more especially to the Colorado potato beetle, originally described as doryphora 10-lineata by Thomas Say. The generic names poly-gramma, myocoryna, and leptinotarsa, applied to it by later European writers, are ignored by Americaii authorities, as founded upon too trifling characters. This insect is indigenous to the cafions and table lands of the Rocky mountains, and began its eastern march from Colorado. In its native habitat it feeds upon various wild species of solamim, particularly S. rostratum and S. cornutum, peculiar to that region. As civilization advanced westward, and field and garden crops were grown within the limits of its natural range, it soon acquired the habit of feeding upon the cultivated potato. Abundance of food stimulated its prolificness, and it gradually extended its ravages eastward.
The first accounts of its injurious propensities were published in 1859-'60, and within 15 years it has spread over the entire potato-growing region of the United States and Canada, and has even excited alarm in Europe. In 1861 it had advanced through Nebraska to the western borders of Iowa, and in the following two or three years it spread itself over the entire extent of this latter state. Its natural history was first made known in 1863, in an article published in the " Prairie Farmer " by Prof. 0. V. Riley. By 1865 it had crossed the Mississippi, continuing its ravages in the potato fields of Illinois and Wisconsin. From these states, in 1867, it invaded western Indiana and the S. W. corner of Michigan, and in 1868 made its appearance in Ohio; and advancing at constantly accelerated speed, it reached the Atlantic states in 1874, and the seabord in 1875. As its native home is subalpine, it naturally thrives best in the north, and in its eastward march it has been observed that its southern columns lag far behind the northern ones. This is accounted for by the fact that the heat and drought of midsummer in the southwestern states prove inimical to it in its immature stages. This insect is not itinerant in the true sense of the word.
It does not march through a country, but in every locality where it makes its advent it establishes a permanent colony. It usually proves most injurious the first year or two after its appearance. Subsequently its numbers are much reduced by the attacks of parasitic and predaceous insects which follow it, or by degrees acquire the habit of preying upon it. - The Colorado potato beetle hibernates in its perfect state beneath the surface of the ground. It has been exhumed from depths varying from a few inches to several feet, though its habit is not to burrow deeper than 10 inches. The beetles issue from the ground early in May. They fly readily during the heat of the day, and are able to make journeys of considerable extent. They begin laying their eggs upon the young potato plants as soon as the latter appear above ground, and will often work into the ground to feed upon the young leaves before these have fairly shown themselves. The eggs are oval, of a translucent dark orange color, and are deposited in clusters of from 10 to 40 on the under sides of the leaves. The larva) are hatched in less than a week, and are at. first of a dark Venetian red, becoming lighter and acquiring a double row of black lateral spots as they approach maturity.
The legs, head, and posterior half of the first joint are also black. In from two to three weeks these larvae acquire their full growth, after which they enter the earth and undergo their transformations, first to the pupa and then to the beetle state, which last is assumed in about a month from the time of hatching. There are three broods or generations each year in the latitude of St. Louis, yet it may be found at almost any time during the summer in all its different stages. This is owing to the fact that the eggs in the ovaries continue to develop, and are laid in small batches at short intervals during a period of about 40 days in summer. The number produced by a single female averages from 500 to 700. This insect, at first confined to plants belonging to the genus solarium, has in its eastward progress acquired the habit of feeding on several other plants belonging to different genera or even to different families; among these are the cabbage, hedge mustard (sisymbrium officinale), smartweed (polygonum hydropiper), pigweed (amarantus retrqflexus), thistle (cir-sium), mullein (verbascum), lamb's quarter, and maple-leaved goosefoot (chenopodium album and C. hybridum). But it is doubtful whether it would thrive for any length of time on any plant not belonging to the nightshade family (solanaceoi). - As the insect advanced toward the Atlantic, it met with new enemies at almost every step, and these are often so efficient in aiding man in his warfare against it that the farmer should be well acquainted with them.
Upward of two dozen of these enemies of its own class have been enumerated and figured by Riley in his Missouri entomological reports. The only genuine parasite known to attack it is a tachina fly (Lydella doryphora, Riley), somewhat resembling in size and general appearance the common house fly. This fly fastens its tough, oval, white eggs to the body of the doryphora larva, and from them subsequently hatch small maggots, which penetrate the body of their victim, and there feeding on the fatty portions are carried into the ground when the doryphora descends to undergo its transformations, finally causing its death. These flies are sometimes so numerous about an infested potato patch that it is difficult to find an uninfected doryphora larva, and the noise they make is like the buzzing of bees. The next most efficient enemy of the Colorado potato beetle is a heteropterous insect called the spined soldier bug (arma spinosa, Dallas). This bug, which is equally carnivorous in its larva, pupa, and perfect states, is of an ochre-yellow color, and is represented in fig. 3 with a pair of wings closed and the other extended.
Its mode of attack is to thrust its long and stout beak into its victim, and, holding the latter thus impaled, to quietly drain its vital juices and throw away the empty skin. The eggs of this soldier bug are pretty little bronze - colored, caldron-shaped objects, with a convex lid around which radiate 15 or 16 white spines. In its adolescent stages the insect is rounded instead of angular, and more prettily colored. Of the other heteropterous insects that attack the doryphora, strietrus Jimbriatus, periling circumcinctus, reduvius raptatorius, and har-pactor ductus are worthy of note. Among coleoptera or beetles, the ladybirds are the most efficient, destroying great numbers of doryphora eggs; and hippodamia maculata, H. convergens, H. l3-punctata, H. glacialis, coccinella 9-punctata, and mysia 15-punctata have been more particularly noticed. Among hymenoptera, the rust-red social wasp (polistes rubiginosus, St. Farg.) has been seen carrying the doryphora larva to its nest as food "for its young; and among diptera, some of the large asilus flies occasionally capture the beetle and suck out its juices. Among other animals which aid in reducing the numbers of the potato beetle may be mentioned the toad, and perhaps some other reptiles, the rose-breasted grosbeak, and the quail.
Domestic fowls at first refused to touch either the beetle or its larvae; but in many parts of the country they have gradually acquired the habit of feeding upon them, and may with great advantage to the grower be allowed access to the potato fields, or taught to feed upon the insects by confinement in a potato patch. - The artificial remedies against this potato beetle are varied and numerous. It is very important to kill the first beetles which appear in spring, and this can be most safely and conveniently done by aid of a pair of simple wooden pincers. During the first few years after the appearance of this insect in some of the western states, several implements were invented to facilitate its destruction. In hot dry weather most of the insects may be destroyed by knocking them off the vines, and then passing between the rows with a brush harrow drawn by a horse. But the remedy now most generally used is Paris green, mixed with from 20 to 30 parts of flour, middlings, plaster, or other diluent; or in a liquid form, using one table-spoonful to three gallons of water.
Prof. Eiley gives the following directions for using both the powder and the liquid: " The green may be shaken over the vines in various manners, and some persons have found an old sleazy sack, such as those used for table salt, to do good service, when attached to the end of a stick. It is most safely applied by aid of a perforated tin box attached to the end of a stick three or four feet long. The least possible dusting suffices, and by taking the handle of the dust box in the left hand, and tapping the. box with a stick held in the right hand, one can walk rapidly along the rows and regulate the amount sifted. The green cannot well be mixed with the flour or plaster except by the aid of a mill, and for this reason those who mix in large quantities have the advantage. The liquid has the advantage over the powder in that there is less danger from injury in its use, and that it can be effectually used at any time of day; while the powder can be employed to advantage only while the dew is on the plants.
It has, however, some disadvantages: 1, the green is not soluble, for though it quickly gives a green tint to the water when stirred, it soon settles to the bottom, unless kept in suspense by continued stirring or agitation; 2, it settles in spots on the leaves, the natural tendency of the water in finding its level being to carry and concentrate it wherever a drop finds rest and evaporates; 3, too much is wasted on the ground in the sprinkling. I have, therefore, found it much more convenient, on a small scale, to use the powder, where it can be obtained ready mixed by machinery. Applied when the dew is on the plants, it will adhere more uniformly, and it obviates the necessity of carrying about so much water. But whether the green be used in water or as a powder, the flour will prove a desirable addition, since it renders the green more adhesive, and consequently more serviceable; some care will be required in using, however, to prevent its forming lumps. This adhesive quality in the liquid may also be obtained by dissolving dextrine or gum arabic in the water - both, however, much more expensive than the flour." Much has been said against the wholesale use of Paris green for this purpose; but it is the experience of those who have had most to do with it, that there is no danger in its judicious use as here recommended.
It effectually kills the insect without affecting the plant either above or below ground; and what little gets into the soil is converted into an insoluble and harmless precipitate with the oxide of iron very generally diffused. - There is another insect, known as the bogus Colorado potato beetle (dorypliora juncta, Germar), which has always existed in the southwestern states, feeding on the wild horse nettle (solatium Carolinense). It is so much like the genuine beetle that it is often mistaken for it. Yet it will not touch the cultivated potato, and a close examination shows many specific differences between the two species. Compared with D. 10-lineata, the eggs of D. juncta are much paler; the larva is also paler, and has but a single row of black dots along the sides; and the beetle has the second and third lines instead of the third and fourth (counting from below) joined, and the intervening space brown; also a spot on the thighs, which is lacking in D. 10-lineata.
Fig. 1. - Doryphora 10-lineata. a. Eggs. b, b, b. Larvae of different sizes, c. Pupa, d, d. Beetle, e. Enlarged wing cover, showing character of punctures. f. Enlarged leg.
Fig. 2. - Lydella doryphora. (Hair line showing natural size).
Fig. 3. - Arma spinosa. a. Enlarged beak. h. Bug, natural size, with wing extended on one side.
Fig. 4. - Anna spinosa. a. Pupa. b. Larva, c. Egg, somewhat enlarged.
Fig. 5. - Harpactor cinctus. a. Bug enlarged, with hair line showing natural size. b. Its beak, enlarged.
Fig. 6. - Mysia 15-punctata. a. Larva, b. Pupa. c. Prothoracic shield of larva. d. Beetle.
Fig. 7. - Doryphora juncta. a, a. Egg's. b, b. Larvae, c. Beetle, d. Wing cover, showing character of punctures, e. Enlarged leg.