16.4 TRANSACTIONS OF THE ILLINOIS 



except the first two. The ovipositor distinct ; honey-tubes, short but 

 distinct. Legs black, tibife pale. Wings pellucid, veins slender and 

 ciusky, third vein abortive at the base. 



The wingless females are also black ; the abdomen frequently show- 

 ing whitish powdery dots along each side of the back. It is the pupa 

 that presents the peculiar and marked character of the species. When 

 this state is fully attained it equals in length the body of the winged 

 individuals: is oval in shape, with Ithe sides nearly parallel, the anterior 

 end bluntly rounded and the end of the abdomen tapered to an obtusely 

 attenuated point. The head varies in color from black to dull green or 

 olive, dusted over with white powder; thorax, with the anterior half, 

 narrow, black and powdered ; posterior half twice the width of the 

 anterior part, dark greenish or olive color; the abdomen black, with 

 white primrose (or powdered) spots along each side of the back. 

 The eggs, when first deposited, are greenish, but soon become black ; 

 are very minute, regularly oval, and not more than one-fiftieth of an 

 inch long. 



These insects usually select the center of the under side of the leaf 

 as the point for locating colonies, which usually consist of but, compara- 

 tively, few individuals. Dr. Fitch thinks this species passes the winter 

 ill the perfect winged state as well as in the egg state. 



30. Aphis circcezandis, Fitch. 



Is a species found on the leaves of Galhon circcBzans. Length about 

 one-eighth of an inch to the ends of the wings; head and thorax, black ; 

 wings, pellucid. 



31. Aphis {Siphonophord) avence. Fabr. The Grain Plant-louse. 



This, which has long been known on wheat, oats, barley and rye, 

 has doubtless been imported frOm Europe, where it has been described 

 under various names, as ^4. avence, Fabr. ; A. granaria, Kirby; A. cerealis, 

 Kalt., and A. hardei, Kyber. Occasionally, of late years, it has become 

 quite too common upon the wheat crops of our Illinois farmers, some- 

 times considerably affecting the yield of this cereal. In 1866 it appeared 

 in various parts of the State in sufficient numbers to do considerable dam- 

 age; and again this fall (1876) it has made its appearance in the young 

 wheat in Illinois. 



They are seen during the season in three different forms, the winged 

 females, the wingless females, which are far more numerous than the 

 winged ones, and the young wingless larvae. Pupae, with minute rudi- 

 mentary wings like scales, may also occasionally be seen. They are 

 furnished witli moderately long honey-tubes, and the females have also a 

 distinct ovipositor or tail-like process at the end of the body ; the males 

 are destitute of this i)rocess. 



In England, according to Curtis, this species presents the following 

 characteristics : 



