PROCEEDINGS OF THE 



ENTOMOLOGICAL SOCIETY OF WASHINGTON 



VOL. 23 NOVEMBER 1921 No. 8 



SOME SUGGESTED HOMOLOGIES BETWEEN LARVAE AND 

 ADULTS IN SAWFLIES. 



BY WILLIAM MIDDLETON, Bureau of Entomology. 



Introduction. 



The following paper, which is a contribution from the Branch 

 of Forest Insects of the Bureau of Entomology, was prepared 

 under the direction of S. A. Rohwer and presents some of the 

 results of a study of the metamorphosis of the gooseberry saw- 

 fly, Pteronidea ribesii Scopoli. The homologies, between the 

 larval areas and the adult sclerites here indicated are only 

 suggested as the author does not believe they are founded on 

 sufficient evidence to be considered as conclusive. The chief 

 value of these suggested homologies lies in the fact that they 

 summarize a series of observations on the external appearance 

 of the larval areas of a sawfly secured by a study of its meta- 

 morphosis and that they form a small part in the controversy 

 of the composition of the insect segment and origin of post- 

 scutellum. Their chief weakness lies in the fact that as yet 

 they are not supported by definite anatomical and histological 

 evidence. 



The composition of the tergum of the segments of the larva 

 of Pteronidea ribesii Scopoli was given considerable attention, 

 especially the limits of the segments and the relations that the 

 areas bear to each other, segment to segment and abdomen to 

 thorax. The results obtained by these studies are supported 

 by successful application to other sawfly larvae representing 

 well separated groups. 



For the time being, the author does not adopt for the tergal 

 areas of the larva the names of the adult parts to which they 

 apparently give rise, but prefers to use a system of lettering and 

 numbering. Such a method of referring to the various parts 

 of the larval tergum makes it possible to describe it and in this 

 paper has the added advantage of not making it necessary to 

 repeat the words "of adult" and "of larva." 



Method of Study. 



The insect chiefly under observation \vus Pteronidea ribcsii 

 Scopoli (the ( Jooseberry Sawfly) which was chosen because it is 



