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DESCRIPTION AND DISCUSSION OF SPECIES. 



Thk Woolly Aphis. 

 ( S('/u':o/iiy/rii /(m/orm . ) 



This insect is especially injurious to young- apple-trees, first in 

 the nursery and then in the orchard. It is most abundant and 

 does its principal damag-e on the roots of the trees, but spreads 

 also to the bark above g-round, where it is particularly likely to 

 appear on the young sprouts which start up from the root of an 

 injured or unhealthy tree. Where abundant it forms bluish-white 

 cottony patches, not unlike some kinds of mold, which on careful 

 examination are seen to consist of a crowd or layer of minute slug- 

 g-ish insects, their bodies covered with a cottony coating which gives 

 the general effect described. They are usually most abundant on 

 the roots, but sometimes appear above ground also on the bark of 

 the trunk or branches. On the exposed parts of the tree they are 

 most likely to be noticed about the collar and at the forks of the 

 principal branches, or wherever an injury to the bark has left a 

 scar. When trees in a nursery or young- orchard have a sickly look — 

 the leaves dull and yellowish — and are not growing well, the pres- 

 ence of this insect on their roots may be suspected even though 

 there may be no appearance of it on the bark above g-round. If 

 the roots of such an infested tree be examined they will commonly 

 be found distorted and deformed with hard knot-like enlargements, 

 many of them almost dead, or even in course of decomposition. 

 (^Fig. 1, ,^4.) These g-all-like growths occur on roots of all sizes to 

 a depth of a foot or more beneath the surface. Unless the tree is 

 so far g-one that the insects have deserted it, they will commonly 

 be found upon these injured roots at all seasons of the year. 



The apple is the only tree liable to attack by this insect, the 

 current supposition that it may live on the roots of forest trees 

 being an error due to confusion of injury by the woolly aphis with 

 that by the root-rot. As it lives underground at all seasons of the 

 year it comes to infest more or less g-enerally the soil itself, 

 although this may be cleared of it by a few months' thorough culti- 

 vation sufticient to destroy etYectively all living apple roots. Like 

 many other plant-lice, the woolly aphis multiplies throughout 

 the greater part of the year by the birth of living young from gen- 

 erations of wingless females only, but in October or November 

 winged females appear somewhat abundantly, and, flying freely, 

 especially before the wind, distribute the species widely. From 

 these descend in the same autumn a generation of males and 

 females, the latter of which eventually lay each a single winter egg-. 



