186 TRANSACTIONS OF THE ILLINOIS 



the apterous specimens, except that they had but little of the down\- 

 substance on their bodies, which were nearly black and rather plump. 

 The fore wings were large, and had three discal (branch) veins, the third 

 one forked near the middle, and scarcely visible near its base before fork- 

 ing. The stigma, or colored spot, was about three times as long as 

 broad, and acute at each end. The hind wings were about half as long as 

 the others, and quite narrow, with two simple discal veins. 



Let us now turn to the other species, the Apple-root louse {Pemphi- 

 gus pyri^, and examine briefly its history and habits, and what relation it 

 has to the other species that has induced me to speak of the two together. 



This species was originally described by Dr. Fitch, in 1851, as Erios- 

 omapyri, but afterwards (1855) transferred by him to Pemphigus, because 

 the third vein of the fore wingsof his specimens were simple, and not forked. 

 Mr. Walsh, in volume I. of the Proceedings of the Entomological Soci- 

 ety of Philadelphia, and in The Practical Entomologist (1866), declared 

 the two species to be distinct. In the latter, he states, in answer to a cor- 

 respondent from Pennsylvania: "You think that the ^//«> that causes 

 warts or knots on the roots of young apple trees in the nursery is the same 

 insect as the Woolly Aphis that lives on the twigs. You are, undoubtedly, 

 mistaken, for they cio not even belong to the same genus, much less to the 

 same species. The Woolly Aphis is Eriosoma lanigera, the Apple-root 

 Aphis is Pemphigus pyri.''' 



In his first report as Acting State Entomologist ( 186S) he repeats 

 this declaration emphatically, and proceeds not only to give the differ- 

 ences between the characters of the two species, but also of their habits, 

 contending, after Blot, that the former is exclusively northern, while the 

 latter extends more southward. He also states in reference to the Woolly 

 Aphis: "It is now, however, pretty clearly ascertained to have existed 

 on the continent of Europe from time immemorial, and it probably emi- 

 grated thence into England on imported apple trees." It is proper to 

 add, that up to this time Mr. Walsh had not succeeded in obtaining any 

 winged individuals of the Apple-root Aphis, but had relied implicitly on 

 Dr. Fitch's description. In an article on this species by the editors of 

 The American Entomologist (January, 1869) the winged individual is de- 

 scribed and figured from a number of specimens, but differing essentially 

 from Dr. Fitch's description. Not only is it much less, but does not even 

 belong to the same genus, being a true species of Eriosoma, with the third 

 vein of the fore wings forked. The authors, upon marking this discovery, 

 came to the very reasonable conclusion that Dr. Fitch was mistaken in 

 believing his specimens belonged to the Apple-root louse ; that they must 

 have been stray specimens which had in some way become intermixed with 

 his specimens of the latter species. They also argue from the habitats of 

 the two species (the Root-louse and Woolly Aphis), and from the fact that 

 this works on the roots, while the E. lanigera works on the trunks and 

 branches, that the American species is not identical with the European, and 

 that the latter is unknown in the United States. This article was, in 

 great part, transferred by Prof. Riley to his first annual report (1869), 

 without any dissent to the views there expressed; but in his third report 



