Sept 4 1916 Life History of Army Cutworm 881 



NUMBER OF BROODS 



From the foregoing observations it is clearly evident that the army 

 cutworm passes through but one annual life cycle. There is not time 

 enough for a second brood to occur between the appearance of adults in 

 the early part of July and the laying of eggs about October 1 . Nine days 

 is the sortest incubation period the writer has noted. The only accurate 

 data of the writer regarding the duration of the larval stage were obtained 

 by rearing to maturity in a heated greenhouse in the winter of 191 5-1 6 

 the various lots of eggs laid by moths in October, 1 91 5. It is believed that 

 the larval period in the greenhouse was probably shorter than it would 

 have been out of doors even in the summer time. The longest period 

 recorded was 118 days, the shortest 96, and the average was 104.06 days. 

 As stated above, the shortest pupal period secured in the indoor rearings 

 was 43 days, which added to the minimum periods gives 148 days, while 

 from July 1 to October 1 there are only 92 days, thus leaving a difference 

 of 56 days. Moreover, no larvae have been found at any time during the 

 summer which might belong to a second brood. 



Observations given in previous paragraphs which have a bearing on 

 this question may be recapitulated. Moths caught in June and July are 

 bright and fresh; those caught in the fall are rubbed and faded. The 

 ovaries are immature in July, while in September and October they are 

 mature. Moths placed in cages at Bozeman in July and given honey 

 w r ater and clover blossoms daily lived until late in September. 



If it be assumed that the brood of moths emerging in June and July 

 live over until fall, meantime growing ova, then the 12 months of the year 

 are all accounted for in one life cycle of the insect. 



SUMMARY 



From the foregoing observations the life history of the army cutworm 

 (Chorizagrotis auxiliaris) may be summarized as follows: 



(1) Egg laying was observed from September 30 to October 12, but 

 possibly occurred for some weeks previous to September 30. 



(2) The moths deposit the eggs directly upon the bare soil. 



(3) The incubation period is about nine days indoors, but hatching 

 may be delayed by lack of sufficient moisture. 



(4) The larvae feed for a variable period in the fall which terminates 

 with the onset of winter. 



(5) The insect hibernates as a partly grown larva. 



(6) Activity is resumed by the larvae with the beginning of plant 

 growth in the spring. 



(7) The larvae feed until about the first week in April, when they enter 

 the earth for pupation. 



(8) The moths emerge from the latter part of June to the middle of July. 



(9) The moths live over until fall, growing ova on food obtained as 

 adults. 



(10.) The army cutworm is single brooded in Montana. 



