THE HORSE-RADISH WEBWORM. 



75 



Only a few adults of the fourth generation issued during October, 

 and these deposited no eggs. The majority of the larvae of this 

 generation went into hibernation about the middle of October. 

 These larvae will hibernate among dead leaves and in cracks in the 

 soil and develop moths during April of the following spring. It will 

 thus be seen that the larval stage of the fourth generation may vary 

 from 27 days to 6 months. 



EGG-LAYING RECORD. 



On May 3 a female issued and mated with a male which had emerged 

 a day earlier. The pair, while still in copulation, was isolated in a 

 cage containing a wad of absorbent cotton saturated with diluted 

 honey and a horse-radish leaf. Eggs were deposited as follows: 



May 4 



May 5 and 6.. 



May 7 



May 8 



May 9 



May 10 



May 11 



May 12 and 13 



May 14 



May 15 



May 16 



May 17 



May 18 



No. of eggs deposited. 



29 



39 



15 



27 



18 



12 



21 



15 



7 



13 



13 



9 



12 



May 19 and 20. 



May 21 



May 22 



May 23 



May 24 



May 25 



May 26 



May 27 



May 28 



May 29 



May 30 



No. of eggs deposited. 



36 



16 



12 



7 



4 



3 



6 



8 



3 



3 



3 



Total. 



331 



The moths were observed copulating May 3, 8, 13, and 20. The 

 male died May 28 and the female June 4. The length of life of the 

 male was 26 days and of the female 32 days. 



The rearing records were obtained in the laboratory at Rocky 

 Ford, Colo. The cages were placed in a window which was kept 

 open night and day. Food was supplied the moths by putting in 

 wads of absorbent cotton which were saturated with honey and water. 

 This food was eaten eagerly. In the cages the moths were quiet and 

 easily controlled. In all cases the larvae were fed with horse-radish 

 leaves. 



NATURAL ENEMIES. 



Only one natural enemy has been found preying on this species at 

 Rocky Ford. This is a small, wasp-like hymenopterous insect 

 which Mr. H. L, Viereck has described as Angitia plutellse n. sp. This 

 parasite is evidently largety responsible for checking the increase of 

 the Plutella larvae. The adults were found in the field from the 

 latter part of April until the middle of November. In the cages the 

 first adults developed from overwintered Plutella larvae on April 23 

 and 27. It is probable that the parasites live through the winter as 

 eggs or larvae within the bodies of the hibernating Plutella larvae. 



