224 OHIO EXPERIMENT STATION: BULLETIN 332 



As previously stated, the eggs of both species hatch with the 

 appearance of the fohage in the spring. 



Both the fall and the spring cankerworms have but a single 

 brood per year. 



Nature of work. — The chief harm inflicted by cankerwoims is 

 the destruction of all or part of the foliage of the host. (See Plate 

 XXVIII, Figs. 2 and 3.) If the insects are plentiful the tree may 

 be entirely stripped of its leaves, and if the infested area is extended 

 it presents the aspect of having been overrun by fire. Several 

 successive recurrences of the scourge is sufficient to kill the trees, 

 and this not infrequently occurs under Ohio conditions but more 

 often farther west, particularly if the visitation is succeeded by a 

 dry, unfavorable summer. In the case of fruit trees and particu- 

 larly apples, the young fruit is sometimes badly mutilated ; but even 

 if this is untouched by the caterpillars, the weakened condition of 

 the tree due to the impairment of its foliage seriously injures the 

 size and quality of the fruit. Always the top of the tree, whether 

 it be fruit or forest, is most severely injured; indeed, the top half 

 may be all but completely defoliated while the lower limbs may be 

 scarcely touched. 



Food plants. — Cankerworms are cosmopolitan feeders, being 

 able to subsist on a wide range of trees and shrubs. Of the fruits 

 apple is much preferred, and plum is occasionally injured. Of the 

 shade and forest trees the linden or basswood suffers more severely 

 than other species, through elm and maple are almost equally 

 harmed. Other host trees observed in Ohio are red oak, white oak, 

 white ash, black oak, chestnut, Craetegus, European linden, beech, 

 ironwood, black walnut and shellbark hickory. Doubtless by fur- 

 ther investigation this list could be enlarged considerably. 



Distribution. — Not only are cankerworms known to infest all 

 sections of the State, but they abound in many other sections of 

 the United States as well. In Ohio the pest most frequently infests 

 the farm orchard and woodlot, but at present it is occurring in 

 exceedingly destructive numbers in the Middle West under city con- 

 ditions whole streets being defoliated by it. 



It is an irregular visitant, its appearance in a community 

 usually starting with small numbers, which gradually increase until 

 the outbreak assumes the proportions of a scourge. This may last 

 for two or three seasons and the pest may then suddenly almost dis- 

 appear. For the last 3 years the pest has gradually increased in 

 plentifulness about Wooster, and as shown in Plate XXVIII, Fig. 3, 

 in some localities in the State has caused an almost complete 

 defoliation of woodlands. 



