Journal of Agricultural Research 



Vol. X, No. I 



until the following spring. Usually the moths remain motionless, 

 although on exceptionally warm winter days they may fly a little if 

 disturbed. 



The moths emerge from hibernation early in May and fly to the blos- 

 soms of cruciferous plants, usually the wild watercress {Roripa sinuata) , 

 to feed. In 1914, I9i5,and 191 6 the overwintered moths were first noted 

 on the wing on May 4, 3, and i, respectively. Copulation takes place 

 shortly after the moths begin to fly, and oviposition commences within 

 a day or two, the eggs of the overwintered females usually being de- 

 posited on the watercress. Occasionally the foliage of turnips which 

 have been protected throughout the winter by snow or stored in pits 

 is available for this purpose. Reproduction continues throughout the 

 summer and until the severe freezes of late fall kill off the last belated 

 larvae and pupae. In the Arkansas Valley the larvae are most numerous 

 in June or early July, the later generations being greatly reduced by 

 parasites. The moths are most numerous during the fall, when they fre- 

 quently occur in considerable numbers about cabbage and other crucif- 

 erous vegetables. 



At Rocky Ford the egg stage covered from 3 to 6 days, the larva stage 

 from 9 to 28 days, and the pupa stage from 5 to 13 days, the life cycle 

 from egg to adult thus occupying from 17 to 47 days. 



In the South the diamond-back moth is active throughout the year, and 

 the larvae are to be found at all seasons. 



LIFE HISTORY OF THE MOTH 



The principal life-history studies of the diamond-back moth were 

 carried out at Rocky Ford, Colo., from 1914 to 1916. The insects were 

 confined in battery-jar cages under open-air conditions. The moths 

 were fed vrith the blossoms (nectar) of cruciferous plants or with diluted 

 honey, and the larvae were reared on cabbage or turnip foliage. 



On May 4, 1914, several overwintered moths which had just issued 

 from hibernation were captured in the field and confined in a cage. 

 Their record is given in Table I. 



Table I. — Record of the generations of Plutella tnacuUpennis at Rocky Ford, Colo., in 



1914 



