16 



Some Notes on Pieris napi. 



By Hugh Main, B.Sc, F.E.S. Read December 12th, 1907. 



Stephens, in his "Illustrations of British Entomology," in 1827, 

 speaking of the species composing his genus Poniia, embracing 

 brassicce, rapce, napi, daplidice, and cardamines, says that " from the 

 simplicity of their colouring and their common appearance, they have 

 been unworthily neglected in this country by collectors, and in con- 

 sequence we still remain unacquainted with the history and meta- 

 morphoses of some of the species which evidently are far from 

 uncommon." 



He divided our brassicce into two distinct species — brassicce and 

 chariclea — rapce into rapes and metra, napi into napi, napcece, and 

 sabellicce, but, as he says, he does this with diffidence, and not without 

 repeated examination, trusting that by so doing he might incite some 

 zealous entomologists to investigate them, and endeavour to unravel 

 the mystery which shrouds the views of the specific identity of these 

 insects. 



In Stephens' time there was no band of workers whom he might 

 enlist for the clearing up of the difficulties he came across in writing 

 his book. Since his time much has been done, but still much 

 remains to be done to clear up points in the life-history of even our 

 commonest species. 



Pieris napi is an insect which has always had a great interest for 

 many of the members of this Society. On looking through the 

 pages of our " Proceedings " many references to it may be noted. 



In February, 1892, Mr. Jenner Weir read a paper on P. napi and 

 allied forms, and there was an exhibition of this species on the same 

 evening, the object of which was, in his words, "to show the effect 

 of environment and season of emergence on the intensity of colora- 

 tion both on the upper and undersides of the wings." He summed 

 up the seasonal differences thus : — " The male of the spring form is 

 lighter above and darker underneath than the same sex of the 

 summer emergence, and the female of the spring form is less black 

 above though more dusky and much darker below than the female 

 of the summer emergence." 



This is, generally speaking, quite true. 



The spring males and females have grey tips to the fore-wings, 

 whereas those of the summer have black tips. In the summer males 

 the central spot of the fore-wings is large and black. In those of the 

 spring it is, when present, not so black and is smaller ; frequently 

 it is absent. 



Occasionally, as shown in some of our Irish summer specimens, a 



