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THE SPRING CANKER-WORM. 19 
shell becoming more or less concave centrally. Shortly before hatch-- 
ing the eggs become quite dark, due to the color of the larva within. 
Eggs secured from females in confinement on the nights of March 
8, 10, and 12, and kept under out-of-door conditions in the insec- 
tary yard at the Department of Agriculture, Washington, D. C.. 
were hatching April 10, 11, and 14, respectively, giving for this stage 
a fairly uniform period of thirty-two to thirty-three days. The 
effect of warm weather upon the development of the embryo may be 
judged from the fact that eggs kept in the insectary at a temperature 
of 65 to 70° F. hatched in about eleven and one-half days. 
When just hatched the spring canker-worm is quite small, measur- 
ing but 1.25 to 1.5 mm. in length, varying with the extension of the 
body. The head is about 0.25 mm. wide, which slightly exceeds the 
width of body across thoracic segments. The head and shield are 
shining black, and the body above dark olive-green, with a distinct 
central longitudinal white stripe centered with narrow interrupted 
lines of the same color as the body. Along each side is a wide irregu- 
lar white stripe, including the spiracles and adjacent tubercles. 
Below, the body is dark yellowish or brownish in color. The thoracic 
legs are stout and dusky exteriorly. There is a single pair of pro- 
legs on the sixth abdominal segment and a pair of anal prolegs. 
The larve come from the eggs about the time the leaves of the 
apple are pushing out, and the latter are at once attacked. At first 
only small holes are eaten through the leaves, but later, as the larve 
grow, the entire leaf substance save the midrib is devoured. (See 
ma. AIT, fios. 6, 7.) 
After three or four weeks of feeding, the time varying much with 
the temperature, the larve have become full grown. They then meas- 
ure from 18 to 23 mm. (0.7 to 0.9 inch) in length. Considerable 
color variation is likely to occur, some specimens being ash-gray, 
green, or yellow, but the predominating color is dark greenish olive 
or blackish. There are two pale narrow lines down the back, centered 
with a broader dark stripe and a whitish stripe along each side. 
(See Pl. III, fig. 2.) The larva of this species is readily distin- 
guished from that of the fall canker-worm by the fact that the former 
has but two pairs of prolegs, while the latter has three, the first pair, 
however, on the fifth abdominal segment, being more or less reduced. 
Newly hatched larve placed on apple trees under a large wire 
cage in the insectary yard April 12, 1905, had matured and were 
entering the ground for pupation by May &, and by May 11 all had 
disappeared from the trees. This gives twenty-seven to thirty days 
for the larval existence. The egg and larval stages together require 
some two months, and the remainder of the year, except the time 
spent in the adult condition before ovipositing, is passed in the pupal 
stage in the soil. As has been stated, the insect pupates from about 
