318 



NATURAL HISTORY OF ARTHROPODS. 



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

 than the Colorado potato-heetle, Dormihom deceiidineata. This species was lirst 

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

 specimens taken a few years before, on the uiipn- ^Missonri River, near the base of the 

 Rocky Mountains. This insect, as was later discovered, fed upon sand-bur {Solaiiuin 

 rostratinn) 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 s])reading over the' northern United States at a 

 rate which, until it reached the Mississii)pi River, did not exceed fifty miles a year, 

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

 more railroails, luitil in 1874, it reache<l the Atlantic coast in many places ; a total 

 average annual rate, accordiu''- to Dr. V. \ . Riley's estimate, of about eiirhty-eiaht 

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

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

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

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

 Dorypliora juncta, a s]iecies which has Ijeen often mistaken, even liy entomologists. 



Fig. 354. — nnrijpintra thamlineata, Colorado potato-beetle, eggs auil larva. On the right. />. juiicta. 



for the Colorado i)otato-beetle, although it does not attack the jiotato, but lives u]>on 

 the horse-nettle {Solauum carolineuse). 



Hoth I), decern! ineata and D. Jmictd h.-ive a l)rownish yellow ground color; the 

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

 ject to yariations of exactly the same nature in both species; ujion each elytron are 

 fiye longitudinal black stri]ies, two of which unile at the a]iical end of the elytron. In 

 D. Ji'cemUneata it is, however, always the third and fourth strijje, counting from the 

 outer edge of the elytron, that unite at their tijis; in TJ. jiincta it is always the .second 

 and third, counting in s.-ime way, that unite, while in the latter species the space 

 between the second and third stripes is generally brownish. The legs of I>. juncta 

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

 lineata are black. 



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

 during the season, from ten to forty at .-i 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 hatcli in 

 about a week ; the convex larvw 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 



