HEMIPTERA. 1 67 



conspicuous. When an infested limb is jarred, the Aphids emit a 

 shower of honey-dew. Owing to the abundance of this secretion, 

 the branches and leaves of an infested tree become blackened by 

 growths of fungi, as with the preceding species. 



The Woolly-louse of the apple, Schizoneura laidgcra. — The 

 Woolly-louse of the apple is one of the best known pests of the 

 fruit-grower. In its most conspicuous form it appears on the trunk 

 and limbs of apple-trees. It congregates in clusters of individuals, 

 which are conspicuous on account of the woolly excretion with which 

 their bodies are clothed. They are especially injurious to young 

 trees, the bark of which becomes deeply pitted and scarred by their 

 attacks. The bark apparently ceases to grow at the point of attack, 

 but swells into a large ridge about the cluster of lice, leaving them 

 in a sheltered pit. The lice also frequently congregate in the axils 

 of the leaves and the forks of the branches. This species resembles 

 the grape Phylloxera in having a root-inhabiting form, which causes 

 knotty swellings on the fibrous roots. It is the presence of this form 

 which makes this pest such a difficult one to combat. 



Although this insect has been known since the close of the last 

 century, its complete life-history has not been traced out. As with 

 all the Pemphiginae the transformations of which we know, and with 

 Phylloxera, there is in this species a generation of mouthless, wing- 

 less, and generally degraded sexual individuals. The females of this 

 generation produce each a winter egg. This can be found fn the 

 winter in the crevices of the bark, and in the pits caused by the 

 trunk form. It is frequently enveloped in the dry skin of the sexual 

 female. The trunk type at least of the wingless, agamic form gives 

 birth to living young not enveloped in a pellicle. As the season 

 advances there appears a generation of winged individuals. These 

 are probably agamic; but whether they produce the sexual genera- 

 tion directly or whether there intervenes one or more agamic genera- 

 tions has not been determined. At Washington I have seen both 

 the root and trunk type of the wingless, agamic form maintain them- 

 selves throughout an entire winter without the intervention of a 

 winter egg. I presume this is a common occurrence farther south. 



As one form of this insect works deep in the ground upon the 

 fibrous roots of the trees, the same difficulties are nut in attempting 

 to destroy it that are presented by the grape Phylloxera. In fact, 

 except in case of an especially valuable tree, I do not believe that it 

 will pa\- to attempt to save a tree that has become badly infested by 

 the woolly aphis. It will be cheaper to dig the tree up ami burn it, 



