THE POTATO TUBER MOTH. 23 



In the field, where the larvae were workmg on potato tops, the pupae 

 were noted m the f oUowmg places : (1 ) In curled dried leaves on the 

 plant; (2) under clods and rubbish, and (3) protruding from old 

 burrows m the stem. 



Under field conditions most of the pupae were found in the dried 

 leaves which still clmig to the potato plant. 



After the larva has completed its cocoon it spends a period varying 

 from two days to a week or more before changmg to the pupa. The 

 larva becomes greenish aU over and sometimes takes on a famt blue 

 tinge. It also becomes much shortened and constricted at the seg- 

 ments, and loses nearly aU its activity. This stage varies very much 

 with the temperature, being much shorter in summer than in wmter. 

 The larva is helpless at this time and can not move within its cocoon 

 sufficiently to ward off the attacks of parasitic enemies. During 

 this period the greatest amomit of parasitism of the mature larva 

 takes places. 



THE PUPA. 



As the time of pupation approaches, the skin on the dorsum of the 

 anterior segments of the larva splits, and the pupa works the skin off 

 in a short time. The cast skin occupies a small space in the posterior 

 end of the cocoon. 



The pupa when newly formed is white with greenish markings. 

 It soon begins to darken and in a few hours' time is uniformly dark 

 brown. When first formed it remains quiet until it becomes hard- 

 ened, but is very sensitive and if disturbed turns itself around by 

 moving the tip of its abdomen in a circle. The hooks at the tip of the 

 abdomen are sometimes fastened in the cocoon, so that even if part 

 of the anterior end of the cocoon is torn off, the pupa will not neces- 

 sarily be dislodged. Just before emergence it is quite active. and 

 turns itself around quickly if disturbed. As the time for emergence 

 approaches the pupa becomes still darker in color and is less active. 



The period of pupation varies greatly with the temperature and 

 even when under constant temperature. Lots of pupse formed on 

 the same day vary to such an extent that the last to emerge often 

 requires twice as long as the first. Experiments undertaken to de- 

 termine the influence of sox on the length of the pupal period gave 

 entirely negative results, as both sexes were practically evenly divided 

 at all periods of emergence. 



Extreme variations for the pupal period indicated 8 days for 

 July and 56 days for December and January. Variations (hn-ing 

 one month includf; 12 days for the shortest and 29 days for the 

 longest ponod. 



Even where lh(! pupal stage is of the longest duraticm the ratio 

 of this to the increased length of the other stages of the moth re- 

 mains so n(!arly constjirit, that, it, s(HMns (h!V(^]()p]n('nt wit,hin the 



