60 



PAPERS ON INSECTS AFFECTING VEGETABLES. 



winter. It will thus be seen that about half the webworms of the 

 second generation and all of those of the third generation, which 

 have not been destroyed by parasites or through artificial or natural 

 agencies, live through the winter in their tubes in the soil. These 

 ki worms " pupate late in the spring and the moths which issue deposit 

 eggs for the first generation. 



The moths when depositing eggs are often to be found in the beet 

 fields in enormous numbers, and when disturbed may be seen flying 

 close above the beet leaves in " clouds." When such numbers of moths 

 are observed in a beet field they should serve as a warning to the 



Fig. 11. — A medium sized sugar-beet plant defoliated by the sugar-beet webworm in July. 



(Original.) 



grower that a " crop " of webworms may be expected within the next 

 week or 10 daj^s. 



As a rule the first and second generations are the most destructive, 

 the third generation, which is actually only a partial one, rarely 

 causing serious damage. It seldom happens that the "worms" of 

 successive generations infest the same patch of beets to a serious ex- 

 tent. Thus a certain field ma}^ be infested by the webworms of the 

 first generation, while the moths which develop from them ma3 7 drift 

 to adjoining fields to deposit eggs for the next generation. 



The webworms often appear very suddenly and apparently with- 

 out warning in certain fields, and it is not uncommon for the growers 

 to express the idea that they have migrated from adjoining fields. 



