Effects of Castration in Insects 



379 



2. The number of male Polistes increased very suddenly Aug- 

 ust 23 to 27 and then fell off still more abruptly. Apparently 

 these collections were made at the time of the emergence of the 

 male brood for the particular locality. 



3. The greater difference in the ratio of male to female Polis- 

 tes (i : 6.3) is to be accounted for partly by this temporary 

 appearance of the males and partly, perhaps, by the fact that this 

 sex is much more wary and therefore more difficult to capture 

 than the females. 



4. While the total number of females examined was somewhat 

 more than six times as great as that of the males, the number of 

 females stylopized was fully nine times as great as that of the 

 stylopized males. As the male brood of the wasp appears late 

 in the season this may be due to a partial immunity of this sex 

 from the attacks of the parasites, since Brues ('05) has shown that 

 the triungulin Xenos must enter the wasp larvae in the spring or 

 early summer {vide infra, p. 393.) 



