THE ENTOMOLOGIST. 



Vol. L.] NOVEMBER, 1917. [No. 654 



NOTE ON THE INFLUENCE OF TEMPEEATURE ON 

 THE DEVELOPMENT OF PIGMENT IN PIERIS 

 BAP.E, L. 



By J. J. Lister, F.PuS., F.E.S. 



The spring of the present year was exceptional for the 

 continuance of cold weather to nearly the end of April and for 

 the sudden coming of summer. The maximum and minimum 

 readings of the thermometer at Grantchester (two miles to the 

 south of Cambridge) from January 1st to May 31st are shown on 

 the accompanying chart. 



From March 19th to April 26th there were only four nights 

 in which the temj)erature did not sink below the freezing point, 

 bitter snow storms lasted on till April 10th, and there were only 

 six days in which the temperature rose above 60° F. At the end 

 of April summer came almost with a bound. On May 4th the 

 glass was up to 68° F., and on May 12th to 80° F., and, with 

 the exception of two brief cool spells, the fine hot weather 

 continued throughout May and June. 



It was not till May 2nd that I first saw P. rupee on the wing, 

 and P. hrassicce and napi and C. argiolus appeared on the 4th. 

 Wishing to obtain a good series of the spring brood of rapes 

 (var. metro , Stephens), I took a considerable number, beginning 

 on May 3rd. As usual the males at first exceeded the females 

 in number. I was soon struck with the number of males in 

 which a spot appeared to be absent on the upper side of the 

 fore wing and the apex of this wing was very pale, and I took as 

 many of these as came my way. About the 18th of May it 

 occurred to me that it would be interesting to find the proportion 

 which these apparently spotless forms bore to the commoner 

 form of male, and from that date till the 25th I took all males in 

 fairly good order that came my way, without any selection. To 

 my surprise, I now found that there were none of the spotless 

 form among the fifty males collected in these eight days. Later, 

 on June 4tb, I took one more, a rather torn specimen with 

 imperfect fringes. With this exception the dates of capture of 

 the apparently spotless males all fall in the first fortnight of May, 

 viz. one on May 3rd, four on the 4th, one on the 5th, one on the 

 7th, two on the 8th, one on the 9th, two on the 11th, one each 

 day on the 12th, 13th and 14th, and one on June 4th. 



These specimens evidently approach the form of the spring 



ENTOM. NOVEMBER, 1917. X . 



