RILEY REMARKS ON CANKER-WORMS, ETC. 279 



the ground within three weeks from hatching. The chrysalis is 

 not formed till about a month afterwards, whereas vernata takes 

 on this form two or three days alter entering the ground. 



The practical lessons to be drawn from the differences here 

 pointed out between these two Canker-worms have been set forth 

 in the report already cited. Palcacrita vernata rises from the 

 ground mostly in early Spring, for which reason I have popularly 

 designated it as the Spring Canker-worm. The principal efforts 

 to prevent the female from ascending the tree should, therefore, be 

 made at that season. The cocoon being fragile is easily broken 

 by any disturbance of the land, and, as the chrysalis is more lia- 

 ble 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. Anisopteryx pome- 

 taria, 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 injuries. 



Both species attack fruit and shade trees ; but while vernata 

 is common and very injurious in the apple orchards of the West- 

 ern 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 En- 

 tomology. 



EXPLANATION OF FIGURES. 



Fig. 14. Paleacrita vernata -.-a, full grown larva; b, egg, enlarged, the natural size 

 shown in the small mass at side; c, an enlarged joint, side view; d, do., back view, show- 

 ing the markings. 



Fig. 15. P- vernata-.— a, b, venation of front and hind wings; c, joint of male antenna, 

 from above, greatly enlarged. 



Fig. 16. P. vernata:— a, male moth; b, female do.— natural size: c, joints of her anten- 

 na;; d, joint of her abdomen, showing spines ; e, her ovipositor— enlarged. 



Fig. 17. P- vernata:— Female chrysalis, the hair-line showing natural length. 



Fig. 1S. Anisopteryx pometaria-.— a, b, egg, side and top views; c, joint of larva, side 

 view, showing markings— enlarged ; e, batch of eggs ; /, full-grown larva— nat. size. 



Fig. 19. A. pometaria-.-a, b, venation of front and hind wings— nat. size; c, joint ct 

 male antenna, from the side; d, same from beneath— greatly enlarged. 



