296 Journal of Agricultural Research voi. xxii. no. 6 



FIRST APPEARANCE OF I^ARV^E 



Larvae may appear in the fall. This is proved by the fact that three 

 larvae were found at Wilsall on September 30 and that larvae hatched in 

 the rearing boxes during October and November whenever sufficient 

 moisture was added. Large numbers of larvae must have hatched at 

 Wilsall during the fall of 1918, for as soon as the snow left the ground 

 the following spring fourth- and fifth- instar larvse were found in large 

 numbers. We have no records of injury to wheat during the fall months, 

 but it seems quite probable that in years when there is considerable 

 moisture and mild weather during October and November great damage 

 may be done. 



The larvae begin to feed shortly after the wheat begins to grow in the 

 spring. In 191 9 at Wilsall 80 acres of winter wheat were completely 

 destroyed by May i, which indicates that the worms must have been 

 active 10 days or 2 weeks previous to that date. 



In 192 1 at Willow Creek first-instar larvae were found on March 3. 

 The weather had been warm for about a week, and winter wheat was 

 starting to grow again. No larger larvae could be found, and it seemed 

 as though the very small first-instar larvae must have just hatched. 



PERIOD OF LARVAIv FEEDING 



One of the reasons why Porosagrotis orthogonia is such a dangerous 

 insect is the unusually long period of heavy larval feeding which extends 

 until the middle of June or even to July 10 in the case of late-hatched 

 specimens. Judging from the reports of injury received, the larvae 

 attract most attention during the month of May and the first two weeks 

 in June, differing decidedly in this respect from Chorizagrotis aiixiliaris, 

 which generally has reached the height of its destructiveness by April 

 15 and has practically disappeared by May i. 



The length of the larval stage as determined for 20 larvae, 5 from each 

 of 4 parent moths, under insectary conditions varied from 62 to 151 

 days and averaged 118 days, as shown in Table III. 



All of the larvae were kept under very similar conditions, and no 

 reason has been found for the wide variation. They were always fed at 

 the same time and were kept on one tray in individual rearing boxes, 

 thus giving practically identical conditions of moisture, temperature, and 

 food. In spite of this similarity of conditions we find that larva 2ie 

 pupated 62 days after hatching from the egg, while larva 2 id from the 

 same parent and from the same egg cluster took 124 days, or just twice 

 as long, to reach the same stage of development. The number of instars 

 was also found to vary. Thus the number of larval instars for the five 

 larvae from each of the moths was as follows: Moth 21 — four had 7 

 instars and one had 8; moth D — all five passed through 8 instars; moth 

 42 — two had 7 instars and three had 8; moth 24 — one had 7 instars and 



