THE POTATO TUBER MOTH. 



21 



METAMORPHOSES. 



The instars of the insect show the greatest irregularity, even where 

 conditions as regards food and temperature are kept as nearly uni- 

 form as possible. In determining the molting periods, a large num.- 

 ber of larvae, hatched on the same day, were placed on tubers and on 

 each succeeding day the larvae were dissected from a tuber and pre- 

 served in formalin. For the first two days the larvae were of approxi- 

 mately the same size, but from the time of the first molt the greatest 

 variation was noticeable; when some had reached the last instar 

 others hatched on the same day and feeding on the same tuber were 

 only haK grown . 



This variation was also very noticeable in the hfe-history work. 

 Where the first mature larvae appeared in 18 days, there were mature 

 larvae leaving the tuber for the succeeding 6 days. Table 1 shows 

 the variation in the length of the larval period with larvae from 

 the same egg masses. 



Table 1. — Length of larval stage of the potato tuber moth with larvx from the same egg 



masses. 



Eggs hatched. 



Number 



of 

 mature 

 larvae. 



Dates between which they 

 appeared. 



Number 

 of days 



in emer- 

 gence 

 period. 



1913 



Nov. 5 



Dec.3 



1914 



Jan. 2 



Feb. 2 



Mar. 19 



Apr. 1 



May4 



June 19 



Julys 



Aug. 4 



Sept.! 



Oct. 4 



Dec. 16 and Jan. 4... 

 Feb. Sand Feb. 21.. 



Mar. 2 and Mar. 28.. 

 Mar. 16 and Apr. 4 . . 

 Apr. 21 and May 2. . 

 May 1 and May 12. . . 

 June 2 and June 10. . 

 July 6 and July 14. . . 

 July 21 and July 27. . 

 Aug. 18 and Aug. 23. 

 Sept. 21 and Sept. 30 

 Nov. 3 and Nov. 16.. 



As has been suggested, the rapidity of growth of the larva seems 

 not to be influenced by the amount of food. Larvae developing 

 in leaves, stems, or petioles, grew more rapidly than those in the 

 tubers. In these experiments the larvae were kept on potted plants 

 indoors, and those in tubers were placed in a breeding jar beside the 

 plant. The experiments were carried on under the same temperature, 

 but the larvae in the leaves were more exposed to changes in tem- 

 perature, and whether the greatest difl'ercnce in the time of develop- 

 ment was caused by a variation in temperature or a difference in the 

 characterof thef()od,itw()ul<lbohardt()dot(^rmine. It seems probsible, 

 howev(;r, that the lurv;e iu the potato tops had the most succiilont 

 food, and t lint this made some difference in the time of development. 

 The rcsiihs of the (!.v|)(!riiri('ri(s nvo shown in Table 2. 



