June, '22] 



CRAWFORD & SPENCER: EUROPEAN CORN BORER 

 Effect of Date of Planting on Infestation 



225 



The larval population in badly infested fields attained enormous 

 magnitudes; a dent com field sown May 18th carried an estimated 

 total of 294,152 per acre, a flint field sown on the same day suffered 

 a total loss of at least 65%, supported a total of 258,400 per acre and 

 left when cut, in the stubble (less than 4 inches in height) and the crop 

 refuse, a residue of 43,488 caterpillars going into the winter. 



In general, all things considered, there seems to be no marked prefer- 

 ence for any particular type or variety of corn. The severe loss associa- 

 ted with sweet corns and the flint varieties being due to the early plant- 

 ing, the ability of the larvae to establish themselves and the small di- 

 mension of the stalks. The obvious relatively shght loss in the dent 

 corns being due to the later planting, its vastly greater bulk and its 

 harder and coarser texture preventing a large proportion of the larvae 

 establishing them.selves in the first instar. 



The Infestation of Plants Other Than Corn 



About the middle of July in the very severely infested fields of early 

 sweet com, to a less extent in severely infested flint and to a very slight 

 extent in dent com except in the one severely injured field, the nearly 

 full grown and full grown larvae become restless. At this time larga 

 numbers of them leave the now breaking, shrivelling and drying com 

 stalks and carry on an apparently haphazard migration throughout 

 a period of about two weeks. In the course of this migration as many 

 as 24,400 larvae per acre found their way into the weeds in one field 



