82 



THE AMEEICAN ENTOMOLOGIST. 



two other such sijecies that infest respectively 

 the Hickory and the Oak. Whether any or all 

 of these species likewise infest the roots of the 

 trees upon which they occur, remains to be 

 ascertained. But certainly they can never emi- 

 grate on to the Apple ; for the Apple, the Elm, 

 the Ash, the Dogwood, the Hickory, and the 

 Oak, all belong to difi'erent botanical fiimilies ; 

 and no Plant-louse that lives upon a plant be- 

 longing to one botanical family, can live when 

 transfen-ed to a plant that belongs to a diffcreut 

 botanical family. Even when two plants belong 

 to diflerent genera of the same botanical family, 

 it is not often that the same Plant-louse will live 

 indifferently upon either; and frequently the 

 same Plant-louse will not even live indifferently 

 upon two plants that belong to the very same 

 botanical genus. We have a I'emarkable exam- 

 ple of this last fact in the common Currant 

 Plant-louse, which swarms in almost every gar- 

 den upon the Currant, and yet was never known 

 to shift its quarters on to the Goosebcny— a 

 species that belongs to the very same genus 

 (Bibes) as the Currant. Indeed so far is this 

 from being the case, that nobody ever saw 

 Plant-lice of any kind whatever infesting the 

 Gooseberry. 



[Fig. 70.] 



e y 



Colors— (6) dull lead color; (c) black. 



Fig. 70, b, shows the Apple-root Plant-louse in 

 the larva state, with the usual wooly matter 

 attached to its back. Fig. 70, c, shows the same 

 iusect in the perfect or winged state, with the 

 wooly matter all removed.* On comparing 



* We annex the technical description of this Plaut-lousc, 

 Irawn up from the neent specimen. 



Thf. Ai-i-i.i;-ii...,t l'L.\XT-i,.,r-r. (Knosoma pyri. Fitch.) 

 (lack, Antrn.Ke --.-.Ihs a.^ lun- a> tlu- ImkIt, joints 1 and 2 al- 



l black; .stiRm^t nale brown, 2} to 3 times as lomias wide, 

 ntcd at botli ends, but more acutely so on the basal end, 

 vein bonnding it behind robust and black. Discoidal 

 as .anil stignial vein slender .and black, the 33 or forked 



this last with Fig. 71, which represents a Plant- 

 louse that inhabits a large gall on the Cotton- 

 wood, it will be ob.scrved at once that the vein- 



[Fig. 71.] 



Color— Black. 



ingofthe front wingisvcry different. InFig.7(t, 

 c, the third branch-vein is very distinctly forked ; 

 in Fig. 71 it is simple. Nor is this a mere acci- 

 dental variation, but a peculiarity of the genus 

 to which either insect belongs. (Fig. 70, c, genus 

 Eriosoma ; Fig. 71, genus Pemphigus) . Now Dr. 

 Fitch describes and names the Apple-root Plant- 

 louse as belonging to the latter genus (Pemjjhi- 

 l/vs) ; whereas out of 10 winged specimens ob- 

 tained by ourselves at Duquoin, S. 111., in the 

 middle of October, 18G8, upon apple roots and 

 suckers swarming with larvpe, and 3 other 

 winged specimens actually bred October 21 and 

 22 from larvte obtained from Dr. Weed, Musca- 

 tine, Iowa, all without exception belong to the 

 former genus {Eriosoma). And moreover, Dr. 

 Fitch's insect is described as being nearly twice 

 as large as ours. How does this come about? 

 We can only account for it in the following way : 

 Dr. Fitch's winged specimens wei-e but two in 

 number, and they were found by him, the one 

 living the other dead, upon the roots of an in- 

 fested young apple-tree, which had been brought 

 liim from au adjoining county. Hence he verj' 

 naturally, but as we think erroneously, inferred 

 that these two winged Plant-lice belonged to the 

 same species as the minute wingless larva? with 

 which the infested roots were swarming. The 

 truth of the matter probably was, that the two 

 winged plant-lice got upon the infested apple- 

 root by accident, on their road from the nursery 

 to Dr. Fitch's orchard. Indeed we can almost 

 say with certainty to what species they be- 

 longed ; for on comparing Dr. Fitch's very 

 minute and elaborate description with the Beech- 

 twig Plant-louse {Pemphigus imbricator, Pitch), 

 which comes out in the winged state in the very 

 same time of the year as he met with liis two 

 specimens, it agrees sufficiently well to apply to 

 that species. It, on the other hand, we compare 



di.-icnidiil hy.'iliii' ,i;, 1 mi: m1< Ii "ii its b.asal 1. Length to 



Nine .■-pefiiii. i: , ; I rr.m Iowa bred October 21- 



■2.;, G dried oiu^ 1; ..^ I-- , raptured at Duquoiu Octo- 



ber K;. In uiie Willi; "1 ,' -11, jli -iiecimcn there are two stig- 

 mal veins, one incloseil by the other, and the inner one 

 springing from near the tip of the stigma . No apparent vari- 

 ^i — „.u„... — ;.. .1 — ^ «*,...« of the 3d or forked discoidal 



