APPLE-THUNK bark-louse its APPEAEi^NCE. 31 



■wood, it ceases to eject its castings, and consequently weal-ethen 

 left without any clue by which to discover it. Hence the im- 

 portance of searching for it seasonably. 



A sma]I, oblong, flattish, brown Ecale, shaped like an oyster ehell, fixed to the smootb 

 bark ; often in prodigious numbers ; in winter and spring covering a number of minute, 

 round, whititih eggs. 



The Apple Bark-lottse, Aspidiotus concbiformis, Gkelin ; Cocctis arborum linearis, 

 MoDEEB, and others; Iliiispis linearis, Coati.. 



The Bark-louse is, on the whole, the most pernicious and de- 

 structive to the apple tree, at the present time, of any insect in 

 our country. Every where through the northern States it is in- 

 festing the orchards to a grievous extent, causing the death of 

 many trees, and impairing the health and vigor of many more. 

 It appears in the form of minute scales, resembling the 

 shell of a muscle or an oyster in their shape, adhering to 

 the surface of the bark, as shown in the annexed cut. It 

 is no rare occurrence to meet with young trees, the bark 

 of. which is literally covered and crowded with these 

 scales from the root to the end of the twigs, and some in- 

 dividuals finding no vacant spot upon the bark where they can 

 fix themselves, are driven to the leaves and the fruit, for upon 

 these one or more of these scales may sometimes be found. And 

 where a tree continues to be thus infested, year after year, it 

 dwindles away and finally dies. I have observed this to be the 

 case especially with young trees standing alone in fields, where, 

 when the vigor of the tree becomes impaired, the insect has no 

 other tree to which it can migrate, better adapted for its suste- 

 nance. Other trees have been noticed as overrun by this insect 

 for a year or two, when, probably from the tree becoming so ex- 

 hausted as no longer to be capable of suitably sustaining the in- 

 sects, they cease to affect it, and it, after a few years, recovers. 

 Whether in such instances the insects perish for want of due 

 nourishment, or whether they migrate to other trees, I am unable 

 to say, though I incline to the opinion that the former is the case 

 with Uje chief part of them. 



