22 



BULLETIjST 427, U. S. DEPAETMENT OF AGRICULTURE. 



Table 2. — Length of larval stage of potato tuber moth; comparison of larvse reared on 

 tubers and larvse reared on potato tops. 



LARV^ REARED ON TUBERS. 



Eggs hatched. 



Larvse 

 mature. 



Larval 

 stage. 



Nov. 10, 1915.... 



Dec. 13 

 July 14 



Days. 

 33 



July 5, 1914 



16 







LARV.ffi; REARED ON POTATO TOPS. 



Nov. 10, 1915 



Dec. 7 

 July 18 



27 



July 5, 1914 : 



13 







The process of molting is similar to that in other lepidopterous 

 larvae, the skin splitting down the dorsum of the first few segments, 

 and the larva working its way out through this opening. By far 

 the greater time is taken up in preparation for molting and in 

 resting after the operation. 



LEAVING THE TUBER. 



When the larvse become mature they usually leave the tuber for 

 pupation. If they remain in their channels they come out toward 

 the opening, so that the head of the pupa is just under the skin of 

 the potato. When the larvse leave the tuber they are very active 

 and seldom remain exposed very long. If they are disturbed in any 

 way they throw themselves about until they reach shelter of some 

 kind. They are especially active when parasites are near, and 

 should the latter approach, contort themselves rapidly until the 

 parasite has disappeared. 



When a suitable place for pupation is discovered, an operation which 

 may consume from an hour to a day, the larva begins a cocoon at 

 once, working so rapidly that very soon it is covered with a thin 

 mesh. If disturbed, it will often leave its partially completed cocoon 

 and seek another place to pupate. Sometunes one larva will interfere 

 with another spinning a cocoon to such an extent that the partially 

 constructed cocoon will be deserted by both. Parasites, however, 

 cause the desertion of the greatest number of cocoons by attempting 

 oviposition before the cocoon is completed. 



Cocoons containing pupse of the tuber moth were noted in an old 

 bin in the following places: (1) In the eyes of potatoes; (2) between 

 potatoes (where they touched or almost touched); (3) between 

 potatoes and bin walls; (4) between potatoes and sacks; (5) in folds of 

 sacks; (6) in cracks in bin walls; (7) in nail holes of bin walls; (8) onbin 

 walls; (9) in rubbish on floor; (10) on open floor (mostly naked); (11) 

 in end of burrow with cocoon partly protruding; (12) in old burrows 

 under dry skm of potatoes. 



