finally succumbing to the combined injuries of insects and disease. Injury is three-fold to the plants above ground, and to the tubers in the field, and again in store. The moths oviposit on any part of a plant, on leaves, stems, on tubers in the hill and when exposed in the field and after they are stored.

METHODS OF CONTROL.-It is impossible to reach the tuber worms in their mines, in stalks or tubers growing in the field, therefore we must proceed against this pest in other ways. Several must be employed to insure success. First come clean methods of cultivation, which implies that all infested plants of potato and weeds of the vicinity must be destroyed, as such material affords a breeding place for the insect and its successful hibernation. Sheep and hogs can be utilized in the destruction of the remnants merely by turning them into the field. Crop rotation is desirable, and cooperation is practically a necessity. Where potatoes are extensively grown in a given region their cultivation might be discontinued for a year. Other plants than tomato, eggplant and tobacco would answer as alternates, and leguminous crops are particularly indicated, owing to their value as soil restorers. Careful compact hilling is an effective method in preventing infestation, especially to the tubers. Carelessness in digging, which consists in leaving potatoes in the field over night instead of promptly removing them to uninfested shelter, should be avoided.

The remedy that has been used with best results consists in placing infested potatoes in tight receptacles and treating them with bisulphid of carbon. Several treatments are sometimes

necessary.

The Potato-scab Gnat (Epidapus scabiei Hopk.).—Some forms of potato-scab are due to the attacks of minute whitish maggots with blackheads which feed in decayed spots in tubers as well as upon healthy portions. The detection of these as the cause of scab is due to the investigations of Dr. A. D. Hopkins,'

1 Special Bul. 2, West Virginia Agr. Exp. Station, 1895, pp. 97-111.

from whose publications the accompanying account has been compiled. The most destructive of these is known as the potatoscab gnat which, in its larval or maggot form, measures about one-sixth of an inch in length. It is the young of a wingless female and winged male gnat or midge, somewhat like the fickle midge treated in preceding pages as an enemy to cucumber. The female deposits eggs on tubers in the cellar from autumn to spring. The maggots enter old scab spots or slightly injured places, and under favorable conditions a generation is developed every 20 to 25 days. Later in spring the gnats deposit their eggs in manure or decomposing material, on seed

Fig. 145.-Potato scab-gnat. a, Fly; i, larva, g, egg; h, egg mass, etc. Much enlarged. (After Hopkins)

potatoes and growing tubers in the hill, to which they may be transferred on seed tubers or in decaying matter. Once within the tuber and the conditions remaining favorable, the potato is destroyed; but if the maggots are driven out by natural enemies or the soil becomes dry they di...ppear. The infested places show nearly the same characters as ordinary scab, for which malady it may be easily mistaken. The conditions most favorable to the increase of this pest are moist, damp cellars, and wet weather during the warmer season. They cannot thrive in dry soil or in perfectly dry storerooms. Immense loss to potatoes was caused in West Virginia during 1891 and 1892, in Philadelphia and probably in other sections of the country. Under favoring conditions for their increase, the gnats may be even

more destructive than the fungus, on account of their penetrating while in the larval stages deep into the substance of the tubers, thus rendering them worthless for market.

Methods of CONTROL.-Preventive measures that will at the same time be effective against the scab fungus apply quite as well to the gnats and their maggots. Dr. Hopkins recommends the following measures for protection against injury: "Select sandy or other soils of a dry character in which a crop of surface growing vegetables or grain has been grown the previous year, and from which the refuse has been thoroughly removed in order that the soil may be as free from vegetable matter as possible. Do not use as fertilizers animal manures, lime, ashes, and like substances. If a fertilizer is necessary, use only a ground bone, phosphate, kainit and other commercial fertilizers of a like character. Select smooth and healthy tubers for seed. When the potatoes are dug,

and before they are stored, carefully sort out all tubers showing the least indication of decay, as well as those which are seriously affected with scab. Do not plant the same land in potatoes for at least three years after a potato crop is taken from it."

Soak seed potatoes in a solution of corrosive sublimate or formalin according to directions furnished in the chapter on insecticides. In case a piece of land is especially favorable for the production of potatoes of excellent quality, if the precaution is taken to remove and burn all rubbish, such as potato tops, weeds, refuse tubers, etc., the same land may be, by judicious fertilizing, planted in potatoes every alternate year.

CHAPTER XIV

INSECTS INJURIOUS TO THE TOMATO

IN the introduction to the chapter on insects affecting potato, eggplant, and similar crops, it was stated that nearly all of these insects affect to a less extent the tomato. The species which will be here mentioned affect more particularly the tomato, and exceptionally potato and similar crops. The most important are the tomato or tobacco worms, the common stalkborer, often so abundant on tomato as to be known as the tomato stalk-borer, which has previously been treated (page 199), and the tomato fruit worm, or the corn-ear worm. The aphides which infest potato, eggplant, etc., are likely to attack tomato and there are two additional species which have been observed on the latter. Mealy-bugs, thrips, plant-bugs and other sucking insects also feed on it.

The Tomato Worms.-The large green "worms" that eat tomato leaves are well known. There are two distinct species of them, closely allied, much alike in all their stages, and practically indentical in habits. They are called indiscriminately tomato or tobacco worms and "hornblowers." In the District of Columbia and vicinity, the two species are of nearly equal occurrence as regards numbers on both tomato and tobacco. They are the larvæ of large sphinx moths.

The tomato worm (Phlegethontius quinquemaculata Haw.).— The tomato or northern tobacco worm is nearly as thick as one's little finger, and about three and a half inches long when extended. The horn is larger and less curved, and usually dark in color, whereas the Southern species has a shorter and

1 Rhopalosiphum solani Thos. and Nectarophora erigeronensis Thos.

more curved red horn. On the sides of the body are eight longitudinal stripes which are met by a similar number of horizontal stripes, each segment forming an angle (fig. 146, b). The moth (a) which produces this tomato worm has a wing expanse of four inches or less. It is the paler form, and the bright orange spots on the sides of the abdomen are not so

vivid as in the Southern species and only four in number, whereas the Southern form has five. The hind-wings are marked with zigzag lines more pronounced than in the Southern species. The dark mahogany brown pupæ of both are frequently turned out of the ground by the spade in early spring and later. They are the possessors of a handle-shaped process projecting from the head, that in the present species (fig. 146, c) being longer than in the Southern (fig. 148, c), indicative of the