396 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 2 



length of time required for the incubation of one egg mass at what 

 is probably an average mean temperature for a rose house in late 

 summer. Another lot of egg masses was left in the room where the 

 temperature averaged 70°F. From these we obtained the following 

 results : — 



Number days' incubation 8 9 10 11 12 



Number of egg masses 1 6 6 6 3 



At this temperature a single egg mass requires 10.18 days incuba- 

 tion and so takes 3.51 days longer to hatch at 70° than at 80°F. 



The larvEe when first hatched are extremely minute and closely 

 resemble the leaf in color. They crawl about for three or four days, 

 feeding here and there and growing rapidly. At the end of this 

 period the young larva begins to form a protection for itself by pull- 

 ing two or three leaves together, or more frequently a young larva 

 will fold over a single leaf forming a tube open at either end. The 

 leaves are held together by silken threads. The larva feeds upon the 

 inside of the tube or makes short excursions to adjacent leaves which 

 are pulled down and attached to the original tube, so that as the 

 larva increases in size it also increases the size of the nest. It was 

 frequently observed that when all the leaves of a particular part of a 

 plant had been destroyed the larvae would go to another part of the 

 plant and start new nests. This, however, seems to be dependent on 

 food supply. The length of the larval stage may be seen from the 

 following : — 



Larval period in days. 

 Number of larvae 



The average length of the larval stage is thus 32.69 days at 80°F. 

 There is no doubt but that food conditions may very materially in- 

 fluence the length of the larval stage which is probably somewhat 

 shorter than the above figures indicate. Before pupation the larva 

 draws the leaves together more firmly than usual so that they practi- 

 cally form a cocoon, to the silk of which the pupa is attached by the 

 hooks of the cremaster. The average length of the pupal stage may 

 be seen from the following : — 



Pupal period in days 5 6 7 8 



Number of pupse 13 23 23 9 



This gives 6.41 days as the average of the pupal stage at 80°F. 

 Out of 62 pupse, 35 were males and 27 females. About 30% of the 

 pupae failed to transform. 



