INSECTS 



Immediately after being laid in the fall, the germ 

 nucleus of the aphis egg begins development, and soon 

 forms a band of tissue lying lengthwise on the under sur- 

 face of the yolk. Then this scarcely-formed embryo 

 undergoes a curious process of revolution in the egg, 

 turning on a crosswise axis head foremost into the yolk 

 and finally stretching out within the latter with the back 

 down and the head toward the original rear end of the 

 egg. Thus it remains through the winter. In March 

 it again becomes active, reverses itself to its first posi- 

 tion, and now completes its development. 



The date of hatching of the apple aphis eggs depends 

 much upon the weather and will vary, therefore, ac- 

 cording to the season, the elevation, and the latitude; but 

 in latitudes from that of Washington north, it is some 

 time in April, usually from the first to the third week of 

 the month. The eggs of most insects resemble seeds in 



their capacity for lying inert un- 

 til proper conditions of warmth 

 and moisture bring forth the 

 creature biding its time within. 

 The eggs of one of the apple 

 aphids, however, are killed by 

 premature warm weather, or if 

 artificially warmed too long be- 

 fore the normal time of hatching. 

 In general, the final development 

 of the aphis embryos keeps pace 

 with the development of the 

 apple buds, since both are con- 

 trolled by the same weather con- 

 ditions, and this coordination 

 usually insures the young aphids 

 against starvation; but the eggs 

 commonly hatch a little in ad- 

 vance of the opening of the buds, 

 and a subsequent spell of cold 



Fig. 92. Eggs of the green 

 apple aphis with outer cover- 

 ings split before hatching; 

 below, an egg removed from 

 its covering 



I58 



