318 



NATURAL HISTORY OF ARTHROPODS. 



No chrysomelid has attracted more attention or has been more extensively studied 

 than the Colorado potato-beetle, Doryphora decemlineata. This species was first 

 described by Thomas Say, an early American entomologist, in the year 1824, from 

 specimens taken a few yeai-s before, on the upper Missouri River, near the base of the 

 Rocky Mountains. This insect, as was later discovered, fed upon sand-bur (Solanum 

 rostratum) in its native home, but as the cultivation of the potato was extended west- 

 ward in the northern United States, this beetle found the latter plant so well suited 

 to its tastes that about 1859 it began spreading over the northern United States at a 

 rate which, until it reached the Mississippi River, did not exceed fifty miles a year, 

 but at a steadily increasing rate, as it reached regions with denser population and 

 more railroads, until in 1874, it reached the Atlantic coast in many places; a total 

 average annual rate, according to Dr. C. V. Riley's estimate, of about eighty-eight 

 miles. It is now so common in all the northern States and in Canada that the inhabi- 

 tants of these regions need no figures or descriptions to recognize it, but the people 

 of regions not yet infested may recognize the beetle and its earlier stages by the 

 accompanying figures and a brief description. A figure is added of the nearly-related 

 Dori/p/wra juncta, a species which has been often mistaken, even by entomologists, 



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k-.i' . .- ' '.ft'j f : ^Ks'toaWfcsMt^ea^ fc:-J -.Vvv ' .,\ m\\\v 



FIG. 354. Doryphora decemlineata, Colorado potato-beetle, eggs aiid larva. On the right, D. juncta. 



for the Colorado potato-beetle, although it does not attack the potato, but lives upon 

 the horse-nettle (Solanum carolinense). 



Both D. decemlineata and D. juncta have a brownish yellow ground color ; the 

 prothorax is marked with black spots, usually eighteen in number, but which are sub- 

 ject to variations of exactly the same nature in both species ; upon each elytron are 

 five longitudinal black stripes, two of which unite at the apical end of the elytron. In 

 D. decemlineata it is, however, always the third and fourth stripe, counting from the 

 outer edge of the elytron, that unite at their tips ; in D, juncta it is always the second 

 and third, counting in same way, that unite, while in the latter species the space 

 between the second and third stripes is generally bi*ownish. The legs of D. juncta 

 are pale, except a black spot on the femur, while the tarsi and knees of D. decem- 

 lineata are black. 



The female Colorado potato-beetle lays from five hundred to one thousand eggs 

 during the season, from ten to forty at a time, in clusters on the under side of potato 

 leaves. These eggs are oblong, about 0.06 of an inch long, fastened by one end, and 

 are orange yellow. The eggs of D, juncta are lighter colored. The eggs hatch in 

 about a week; the convex larvae are at first dark reddish brown, becoming paler and 

 brighter in coloration as they increase in size. The full-grown larva is about 0.5 long, 

 with the abdomen much convex above. Along the sides of the abdomen "are two rows 



