﻿18 EIGHTH ANNUAL REPORT 



liable to perish when the cell is broken, fall-plowing of the soil under trees that have 

 been attacked by the worms is to be recommended. The eggs being secreted, for the 

 most part, under loose bark, the scraping of trees in early spring, or any system of 

 keeping them smooth, will act as a preventive of injury. Anisoptery.v pomefaria, which 

 I have called the Fall Canker-worm, rises, for the most part, in the Fall, and should 

 be attacked most persistently at this season. Its cocoon being tougher, and its eggs 

 attached to smooth as well as rough trees, scraping and plowing will effect little in 

 preventing its inj-jries. 



Both species attack fruit and shade trees ; but while vernata is common and very 

 injurious in the apple orchards of the Western States, pometaria is rare there, and most 

 common on the elms of New England. 



These two insects, so long confounded, forcibly illustrate the practical importance 

 of minute discriminations in Economic Entomology. 



• Thus, in addition to the characters pointed out a year ago, we have 

 an important distinction between the two insects, from the practical 

 stand point, in the manner in which the chrysalis state is assumed. 

 The Spring Canker-worm, with its chrysalis formed in a simple earthen 

 cavity, will be very materially aflected by late fall plowing of the soil, 

 especially if the soil be of such nature as to crumble easily ; for I 

 showed in 1869* that whenever the fragile cocoon is broken open, as 

 it very readily is by disturbance of the soil, at that season the chrysa- 

 lis has not the power to penetrate it again or to form a second cavity, 

 and either rots, dries out, becomes moldy or, if on the surface, is de- 

 voured by birds. For the same reason the rooting of hogs is very 

 beneficial in lessening the work of this species. With the Fall Canker- 

 worm, on the contrary, these measures will avail little, if anything; 

 for the cocoon, composed of a thick layer of yielding silk strength- 

 ened by the interweaving of particles of earth cannot be broken 

 open by any such processes, and a dozen plowings would not expose 

 a single chrysalis. Without doubt, we have in these facts a valid ex- 

 planation of the contradictory experience as to the value of fall plow- 

 ing or the use of hogs in an orchard as canker-worm checks. 



In brief, all the more important measures to be pursued in our 

 warfare against the Spring Canker-worm — such as the use of hind- 

 rances to the ascensions of the moths in spring; the removal of all 

 loose bark and keeping the trunk and limb? as smooth and clean as 

 possible ; the employment of hogs, and fall plowing — are, in the main, 

 useless as directed against the Fall Canker-worm which must be fought 

 principally by traps or barriers applied to the tree in the Fall to pre- 

 vent the climbing of the moths which mostly issue at that season. 

 Important points like these cannot be too often insisted on, because 

 I find that our horticultural writers yet very generally speak of the 



* 2nd Rep. 102. 



