INJJRIOUS INSECTS. 



307 



Fig. 2. Apple-tree Root-louse ( Schisoneiira Uini- 

 gera): a, niseased root; b, wingless form; c, 

 winged form; rf, leg; e, beak;/, larval antenna; 

 ST, perfect antenna; all enlarged except a. After iQQjjiQnr gubstance, and 

 Kiley. " ' 



THE APPLE-TREE ROOT-LOUSE. 



f Schizoneura lanigera, Haasln). 



Probably few insects have been the cause of greater disappoint- 

 ment to the apple-grower than the insidious pest above named. Es- 

 pecially is this the case of the inexperienced horticulturist, who plants 



bis trees without careful exam- 

 ination of the roots or of the soil 

 in which they are set, and who, 

 after wondering over their feeble 

 growth, and the fact that a large 

 proportion have languished and 

 died, makes a thorough investi- 

 gation for causes, and finds his 

 young trees, that ought to be 

 about ready to fruit, with their 

 roots knotted and decayed, cov- 

 ered with a bluish white mouldy- 

 alto- 

 gether incapable of holding the tree firmly in the soil or of conveying 

 nutriment to the branches and leaves. Still closer scrutiny reveals 

 myriads of small, pale-yellow lice clustering in the crevices and creases 

 of the distorted roots, all more or less densely covered with the mouldy- 

 looking, cottony matter which is excreted in exceedingly fine threads 

 from the upper surface of the body. The beak or sucker, of which a 

 magnified figure is seen at e in the illustration, is, in the young lice, 

 nearly as long as the body, beneath which it is folded when the insect 

 is not feeding. In more mature specimens, which are often of a pink 

 or purplish color, the beak is proportianally somewhat shorter. As 

 soon as the weather becomes warm, there will be found associated with 

 these more or less numerously, the winged migrant form. The latter 

 are of darker color, and excrete very ^little of the downy matter, so 

 characteristic of the apterous form. They are all parthenogenetic 

 females, and their mission is emigration and the formation of new col- 

 onies on young and healthy roots. 



This species has an aerial as well as a subterranean form. The 

 former is more often found in the New England States than the one 

 upon the roots, and is also so widely diffused over Europe as to make 

 "its supposed" American origin quite doubtful. This form is called 

 woolly aphis with great propriety, as its colonies work under a downy 

 coverlet of the bluish-white excretions. In clay soils, and especially 



