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LITERATURE CITED.

(1) CLINTON, G. P.

1902. Apple rots in Illinois. Ill. Agr. Exp. Sta. Bul. 69, p. 189-224, pl. A-J.

(2) ELLIS, J. B., and EVERHART, B. M.

1895. New species of fungi from various localities. In Proc. Acad. Nat. Sci., Phila., 1895 p. 413-441.

(3) LEWIS, D. E.

1913. The control of apple blotch.

517-574, 18 fig.

(4) ROBERTS, J. W.

Kans. Agr. Exp. Sta. Bul. 196, p.

1915. Sources of the early infections of apple bitter-rot. In Jour. Agr. Research, v. 4, no. 1, p. 59–64, pl. 7. Literature cited, p. 64.

(5) SCOTT, W. M., and QUAINTANCE, A. L.

(6)

1907. Spraying for apple diseases and the codling moth in the Ozarks. U. S. Dept. Agr. Farmers' Bul. 283, 42 p., 7 fig.

and RORER, J. B.

1909. Apple blotch, a serious disease of southern orchards. U. S. Dept. Agr., Bur. Plant Indus. Bul. 144, 28 p., 6 pl. (1 col.).

(7) SHELDON, J. L.

1907. Concerning the relationship of Phyllosticta solitaria to the fruit blotch of apples. In Science, n. s., v. 26, no. 658, p. 183-185.

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WASHINGTON: GOVERNMENT PRINTING OFFICE: 1917

UNITED STATES DEPARTMENT OF AGRICULTURE

BULLETIN No. 535

Contribution from the Bureau of Entomology

L. O. HOWARD, Chief

Washington, D. C.

June 28, 1917

THE HORSE-RADISH FLEA-BEETLE: ITS LIFE HISTORY AND DISTRIBUTION.

By F. H. CHITTENDEN, Entomologist in Charge of Truck Crop and Stored Product Insect Investigations, and NEALE F. HOWARD, Specialist.

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Nearly every year there is brought to this country some insect immigrant, and frequently, in the course of time, these immigrants prove to be pests. As a rule, they are introduced through the large seaports, particularly Boston, New York, New Orleans, and San Francisco, from which points they spread westward, northward, or southward, and less frequently eastward. Occasionally such an insect is carried by commerce beyond the coasts and makes its first appearance inland. This happened in the case of the insect to which the senior author has given the name of the horse-radish flea-beetle (fig. 1) and which is known zoologically as Phyllotreta armoraciae

NOTE. Horse-radish is widely cultivated in the United States and especially where the horse-radish flea-beetle is now most injurious. The farm value of horse-radish is not far from $400,000 per annum, considering its growth for home use. Two other insects than the horse-radish flea-beetle are especially attracted to it, the horse-radish webworm (Plutella armoracia Busck) and the horse-radish caterpillar (Evergestis straminalis Hübn.). Neither of these is of any importance, but in the southern range of growth of horseradish the harlequin cabbage bug is a most destructive pest, seeming to prefer this plant to other crucifers. The horse-radish flea-beetle will continue to spread and soon become a dangerous pest unless growers practice methods of control.

81307-17

Koch. It was obtained for the first time in 1893 on the withered leaves of horse-radish in a vacant lot within a fourth of a mile of the grounds of the Columbian Exposition at Chicago, Ill. It is possible that the species was actually introduced at about that time, but probably the time was one, two, or more years earlier, and it was not reported as a pest until 1908.

The larvæ as well as beetles live on the leaves and petioles of the common horse-radish ([Nasturtium] Radicula armoracia) and when numerous injure the plant to such an extent as to reduce materially the root crop. The larvæ mine the petioles or midribs (fig. 2), while the adults feed on the leaves, causing the characteristic flea-beetle injury-withering and dying or gouge deep pits in the petioles or midribs.

The horse-radish

flea

This beetle belongs to the same genus as the well-known injurious striped cabbage flea-beetle (Phyllotreta vittata Fab.) but may be distinguished readily from all other species occurring in this country by its elytra or wingcovers, which are mostly of a pale cream color with a comparatively narrow sutural black stripe, as shown in figure 1. .

The horse-radish flea-beetle, having recently become an economic factor in the growing of horse-radish 2 on a commercial scale in Brown County, near Green Bay, Wis., the junior author has been able to trace its life economy and history. It first appeared in sufficient numbers to be seriously injurious in the summer of 1914, when it was reported and observed by Prof. J. G. Sanders. In the two years following, the beetles reappeared in large numbers in the same locality.

[graphic]

FIG. 1. beetle (Phyllotreta armoraciae): Adult. Greatly enlarged. (Original.)

While as yet not very generally distributed and confined to attacks on the relatively unimportant crop of horse-radish, the possibility that this insect in its new domain may adapt itself to the other and more important members of the cultivated cruciferous plants renders it worthy of such notice as can be supplied.

1 Order Coleoptera, family Chrysomelidae, subfamily Halticini.

The authors desire to acknowledge the cooperation of the Department of Economic Entomology, University of Wisconsin, and the many favors received from Mr. George B. Smith, Green Bay, Wis., on whose farm the junior author was stationed when many of the data in this paper were obtained.

DESCRIPTIVE.

THE ADULT.

In appearance Phyllotreta armoraciae is distinct from any species of flea-beetle belonging to or introduced into this country. It is somewhat larger and wider than

any of the native species of the genus. It is of oval form, strongly convex, and black in color. The first three antennal joints, the apices or tips of the four anterior femora, the tibiæ, and the tarsi are reddish yellow. The elytra are very light yellowish, or cream color, nearly white, with a very thin black lateral margin and a broadened sutural stripe, widest at the middle and constricted at each end and extending from the base of the thorax to the apex of the elytra, where it joins the lateral line. The frons or front is very finely, and the prothorax and elytra densely, punctate. sensitive pore from which proceeds a seta is located on the lateral margin, which is behind. the anterior angle. In the male the fourth antennal joint is slightly thickened and longer than the fifth. In the female the fourth and fifth joints are equal.

[graphic]

A

The average length is from 3

to 3.3 mm., but individuals have

FIG. 2.-Work of the horse-radish fleabeetle in leaf petioles of horse-radish. (Original.)

been observed where there is a variation of from 2.6 mm. to 3.4 mm. and a variation in width of 1.3 mm. to 1.9 mm.

The following synonymy is recognized:

Phyllotreta armoraciae (Koch).

Haltica armoraciae Koch, Entom. Hefte, v. 2, p. 75, 1803.

Haltica vittata Steph., Mandibulata, p. 292, 1831.

The species is also treated systematically by Illiger, Duftschmidt, Gyllhenhal, Schilling, Redtenbacher, Seidlitz, Foudras, Allard, Leesberg, and others.

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