THE IMPORTED CABBAGE WEB WORM. 41 



EXPERIMENT IN SCREENING A SEED BED. 



On October 18 two cabbage seed beds were planted at Wahiawa. 

 The beds were about 11 yards in length and nearly 1 yard wide. 

 They were separated by a path about 12 inches in width. One bed 

 was screened and the other was left uncovered in the usual manner. 



The screen was made by placing 12-inch boards on edge around 

 the sides and ends of the bed, and over this a strip of cotton cheese- 

 cloth was tacked. This strip of cloth was a yard wide and a little 

 more than 11 yards in length. It cost 5 cents per yard. It was 

 originally intended to make the cover of the fine-meshed, cotton mos- 

 quito netting, but as this netting was not obtainable at the time 

 cheesecloth was used instead. 



These beds were examined November 8. At that date the plants 

 in the exposed bed were well infested by Hellula larvae. The plants 

 in the screened bed were free from insect pests and were larger and 

 in better condition than those in the exposed bed. Their condition 

 was accounted for by the fact that the screen prevented rapid evapo- 

 ration, as Avell as insect attack, and the abundant moisture and free- 

 dom from insects favored a thrifty growth. 



November 18 fully 75 per cent of the plants in the exposed bed 

 were ruined or injured by webworms. The plants in the screened 

 bed were free from webworms and other insect pests and were of 

 sufficient size to transplant. Owing to the protection they had re- 

 ceived and their rapid growth, these plants were quite tender, and it 

 was necessary to remove the cover and expose them to the sun to 

 harden them. After being exposed a little more than a week the 

 plants were well hardened, and several thousand were successfully 

 transplanted. 



A final examination of the transplanted cabbages was made De- 

 cember 23. At that date most of them were growing vigorously and 

 only a few were infested by webworms. 



On the whole this experiment was a success, although it is very 

 evident that a mistake was made in using cheesecloth for the cover. 

 This material shaded the plants from the sun and their growth was 

 too rapid. Undoubtedly mosquito netting would have been an ideal 

 cover. 



CONCLUSION. 



The observations on this webworm have been made under normal 

 field conditions in several localities in Texas, California, and the 

 Hawaiian Islands. Basing an opinion on the studies and experi- 

 ments made in these places, arsenicals can not be depended on to 

 control this species on cabbage. This belief is strengthened by the 

 experience of Mr. M. M. High, who reports, as mentioned on another 

 page of this article, that dry Paris green was unsuccessfully used 

 against this pest on cabbage in Mississippi during 1909. 



