Effects of Castration in Insects 393 



In the case of the male Pohstes the matter is not so readily 

 explained, since this sex is not subiected to the two forms of nor- 

 mal physiological castration just mentioned. But it should be 

 noted that the effects of stylopization on the secondary sexual 

 characters of the male even in Andrena are rarer than in the female 

 {vide, p. 384), owing to the fact that castration is much less 

 complete in this sex, as both Perez and Perkins have shown. This 

 is, no doubt, also the case in Polistes, for the development of the 

 testes requires much less food than does that of the ovaries, and 

 the presence of the Xenos probably, therefore, has much less 

 effect on this sex. 



It has long been known that male puparia and adult femaU 

 Xenos are found only in the late summer or fall brood of Polistes 

 in the brood, namely, which consists of fertile females and males 

 that are to mate and provide, after hibernation of individuals oi 

 the former sex, for the formation of new colonies durmg the en- 

 suing spring. Brues ('05) captured on May 22 a large over-win 

 tered female of P. rubigmosus con taming a female Xenos ni 

 grescens that gave birth to a lot of triungulin larvae. Evidently, 

 therefore, the larvae of the wasp must be infested with triun • 

 gulins in the spring, soon after the colony is founded. How come 

 it then, we are led to ask, that the adult Xenos appear only ir 

 wasps belonging to the last or autumn broods? If these wasp> 

 really belong to so late a brood they could not become infested 

 unless we suppose that the triungulins hang about the wasps' 

 nest for a long period before entering the larvae. As this assump- 

 tion is very improbable, we seem to be forced to the conclusion 

 that the wasps that bear the Xenos in the late summer reallv 

 belong to early broods which have been greatly retarded in their 

 larval and pupal development. Dodd ('06) and Howard ('08) 

 have published some interesting observations which show that 

 the larvae of other insects (Lepidoptera,Formicidae) parasitized by 

 chalcidids are greatly retarded in their growth and development. 

 If this occurs also in Polistes larvae infested with Xenos, as seems 

 probable, we may be able to account for the facts and understand 

 how the single generation of Xenos manages to survive till the 

 following spring to insure the perpetuation of the race in healthy, 



