74 



emigrated thence into England on imported apple-trees.* The Apple- 

 root Plant-louse, on the contrary, is a native American species, and in 

 all probability infested our wild Crabs and Thorns in the olden time, 

 and, when apple-trees were introduced here, saw fit to attack them also. 



In the typical or normal Plant-louse there are in the front wing 

 three branch-veins, springing successively out of the main or rib-vein 

 which coasts along the outer or anterior edge of the front wing. In 

 the genus to which the Apple-root Plant-louse belongs {Pemphigus), 

 the 3d of these branch-veins is perfectly simple; in the genus to 

 which the true "Woolly Plant-louse"' belongs (Eriosoma, otherwise 

 known as Schizoneura or Myzoxylus) , the 3d of these branch-veins is 

 once-forl-ed; in the genus to which the common Apple-tree Plant-louse 

 belongs, (Aphis,) the 3d of these branch-veins is twice-forl-ed. Thus, 

 on the very same Apple-tree, may be found examples of all these three 

 genera — namely, the Apple-root Plant-louse, the true Woolly Plant- 

 louse and the common Apple-tree Plant-louse — all distinct from each 

 other by a very obvious character, and only in very rare and exceptional 

 individuals of any of them running together by intermediate grades. 



Harris indeed, on the authority of Hausmann and Knapp, asserts 

 that the true "Woolly Plant-louse" never has any wings at all.f But 

 Amyot and Serville describe the male as yvmged ,(Hemipt. p. 612); 

 Westwood describes both sexes as winged, though he confounds the 

 genera (Pemphigus and Eriosoma) together, (Introd. II. p. 440 and 

 Synops. p. 118); and lastly Mr. A. E. Verrill discovered in Connecti- 

 cut in October numerous winged specimens, both of the males and of 

 the females. (Practical Entomologist, I. p. 21.) 



The true "Woolly Plant-louse" is a northern species, and accord- 

 ing to the European entomologist. Blot, cannot stand a hot climate 

 even in its native country, Europe, being confined to Belgium, the 

 north of France, Germany and England. Hence, so far, it has oc- 

 curred in this country almost exclusively in New England. The Ap- 

 ple-root Plant-louse, on the other hand, seems to be far more destruc- 

 tive in a hot southern climate than it is towards the north. Again: 

 the true "Woolly Plant-louse" never burrows underground to get at 

 the roots, but inhabits exclusively the trunk and limbs of the Apple- 

 tree, where it secretes large masses of cottony down. The Apple- 

 root Plant-louse, on the contrary, lives habitually underground, suck- 

 ing the sap from the roots and causing thereon large excrescences and 

 swellings, among which it secretes a bluish-white downy substance, 



*See Harris's Injurious Insects, p. 242, and Amyot and Serville's Hemip- 

 tera, p. 606. 



■fSee Harris's Injurious Insects, p. 243. 



