THE SPRING CANKEE-WOKM. 19 



shell l)('C()inin<^ iiioiv oi- less coiicin'c ('(Mitrally. Shoi'tly hoforc liatcli- 

 iiiii' til*' ^'ggs become <iiii(e dark, (lii(> to (lie color of the larva within. 

 E^gs secured from females in confinement on the niiihts of March 

 8, 10, and 12. and kept under out-of-dooi- conditions in the insec- 

 tary yard at the Department of Agriculture, Washington, D. C, 

 were hatching Api'il 10, 11, and 14, respectively, giving for this stage 

 a fairh^ uniform period of thirty-two to thirty-thive days. The 

 effect of Avarm Aveather upon the development of the embryo may be 

 judged from the fact that eggs kept in the insectary at a temi)erature 

 of C);") to TO" F. hatched in about eleven and one-half days, 



A\'hen just hatched the spring canker-worm is quite small, measur- 

 ing but 1.25 to 1.5 mm. in length, varying with the exten-don of the 

 body. The head is about 0.25 nnn. 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- 

 hi) white stripe, including the spiracles and adjacent tubercles. 

 Below, the body is dark yelloAvish or brownish in color. The thoracic 

 legs are stout and dusky exteriorly. There is a. single pair of i)ro- 

 legs on the sixth abdominal segment and a i)air of anal prolegs. 



The larva' come from the eggs about the time the leaves of the 

 appie are pushing out, and the latter are at once attacked. At first 

 only small holes are eaten through the leaves, but later, as the larvw 

 grow, the entire leaf substance save the midrib is devoured. (See 

 PI. Ill, figs. 6, 7.) 



After three or four weeks of feeding, the time varying nnich with 

 the temperature, the larva> have become full grown. They then meas- 

 ure from 18 to 23 mm. (0.7 to O.i) inch) in length. Considerable 

 color variation is likely to occur, some specimens being ash-gray, 

 g> n, or yellow, but the predominating color is dark greenish olive 

 or blackish. There are two ])ale narrow lines down the back, centered 

 A' a broader dark stripe and a whitish stripe along each side, 

 (bee PI. Ill, fig. 2.) The larva of this species is readily distin- 

 guished from that of the fall canker- Avorm by the fact that the former 

 has but tAvo pairs of prolegs, while the latter has three, the first i)air, 

 lioweA'er, on the fifth abdominal segment, being more or less reduced. 



Newly hatched larv;e placed on apple trees under a large Avire 

 cage in the insectary yard April 12, 1005, Inul matured and were 

 entering the ground for pupation b}^ jMay S, and by ^lay 11 all had 

 disappeared from the trees. This gives twenty-seven to thirty days 

 for the larval existence. The egg and larval stages together refjuire 

 some tAvo months, and the renuiinder 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 



