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SOME NOTES ON THE NATURAL CONTROL OF THE OYSTER-SHELL 

 SCALE (LEPIDOSAPHES ULMI, L.). 



By John D. Tothill, 



In charge of Natural Control Investigations, Entomological Branch, 

 Department of Agriculture, Ottawa, Canada. 



The oyster-shell or mussel scale (Lepidosaphes ulmi, L.) (fig. 1) is too well known 

 to need any particular introduction ; suffice it to say that this insect has followed 

 its principal food-plant, the apple tree, over the world. Though usually considered 

 a serious pest in places in which it has been long established, such as England and 



Fig. 1. Oyster-shell Scale (Lepidosaphes ulmi, L.) ; 



a, $ from beneath, filled with eggs ; 6, same from 



above ; c, twig infested with $ scales ; d, <J scale 



and twig infested therewith. (After J. B. Smith.) 



Canada, it is not increasing. There must then be agencies at work destroying annually 

 about 98 per cent, of the progeny of each pair of scales. In different countries these 

 agencies may differ greatly. It is the purpose of the present paper to give a general 

 outline of the principal factors operating in the control of this scale in Canada, and 

 more especially in Eastern Canada. The study, which has been carried on under the 

 direction of the Dominion Entomologist, Dr. C. Gordon Hewitt, is based on the 

 literature of the subject and on the examination of about eighteen thousand 

 egg-masses of scales collected, between September 1916 and April 1917, from 

 representative places throughout Canada. Most of this material was gathered by 



