THE ALFALFA CATEEPILLAR. 11 



EGG STAGE. 



The egg stage varies under ordinary temperatures from 2 to 15 

 days, the normal period being about 6 days. The length of the egg 

 stage as observed for the six generations during the season of 1912 

 is as follows: First generation, 14^ days; second generation, 4 days; 

 third generation, 3 days; fourth generation, 3^ days; fifth genera- 

 tion, 3^ days; sixth generation, 5 days. In the summer of 1913 

 Mr. T. Scott Wilson had eggs under observation which hatched in 

 two days during the month of August, but with an average mean 

 temperature of 87° F., and this same season Mr. E. H. Gibson, at 

 Nashville, Tenn., observed eggs to hatch in an equally short time, 

 with an average mean, temperature of 76° F. Mr. Gibson gathered 

 three eggs on June 5 and noted that the time of oviposition was 3 

 p. m. He placed these in a box, and at 3 p. m., June 7, the larva?, 

 were found emerging from eggshells. Thus the remarkably short 

 period of 48 hours elapsed from oviposition to hatching. 



The eggs are deposited upright, singly, on the upper surface of 

 fresh, green alfalfa leaves. When first deposited they are white in 

 color, but change in a few hours to reddish brown. Just before 

 hatching the upper end becomes light colored or nearly transparent, 

 and the caterpillar gnaws its way out. 



LARVAL, OR CATERPILLAR, STAGE. 



Upon hatching, the larva makes its first meal on the eggshells, 

 often consuming the whole shell. It then feeds upon the leaf, at 

 first gnawing out very small, tiny spots; but rapidly its appetite in- 

 creases, and it is soon consuming the entire leaf, veins and all. Ob- 

 servations made by the writer and by Mr. Watts, a former agent of 

 this bureau, show that one larva consumes about 25 to 30 leaves dur- 

 ing its lifetime. Its growth increases just as fast as its appetite, and 

 often within 12 days the larva is full grown, having cast its skin, or 

 molted, four times and having passed through five instars, or periods 

 between molts, and increased from less than one-tenth inch to 

 nearly 1^ inches in length. The duration of these various instars 

 (see Table II) is influenced greatly by temperature, and during 

 cold or cool weather they are protracted considerably, so that often 

 the complete larval period will cover a month or even more, the 

 general average period for all temperatures being about 24 days. 



The larva in feeding stretches itself along an alfalfa stalk and is 

 often rather hard to find, the green color of its body proving to be 

 exactly the same shade as the alfalfa upon which it is feeding. 



