THE HORSE-RADISH WEBWORM. 
7D 
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 
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 
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 Yiereck has described as Angitia plutellse n. sp. This 
parasite is evidently large 1 y 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. 
