CONTROL OF Two ELM-TREE PESTS 507 



abundant on English elms and that they pass through their life cycle 

 somewhat faster on these trees than on American elms. Therefore, 

 observations confined to individuals occurring on American elms might 

 lead to conclusions concerning the rapidity of development and num- 

 ber of broods different from those resulting if individuals occurring on 

 English elms were observed. 



