NOTES ON THE LIFE HISTORY OF STYLOPID.E. 293 



A study of the conditions in this nest bring to light a number 

 of interesting points. It is seen that seventeen, or almost fifty 

 per cent, of the wasps contained both male and female parasites, 

 while about an equal number contained parasites of only one 

 sex. In these latter the number infested by males and females 

 was about equal. A single wasp contained only larvae, while 

 several bore larvae in addition to imagines. The presence of larvae 

 in full-grown wasps is no doubt due to a failure to keep pace in 

 development with the growth of the wasps. 



From the large number bearing parasites of both sexes, in 

 seems probable that at times the sex of the parasites is in no way 

 influenced by the host, or rather, that the sex of the specimens 

 to mature in a single wasp from the large number of Xenos 

 larvae usually present is not always the same as I had previously 

 supposed from former observations ('03, 246). 



A second point of interest is the considerable number of wasps, 

 seven in all, from which males had emerged before capture. 

 From previous observations upon wasps in captivity ('03) I was 

 led to believe that the hosts died very soon after the emergence 

 of male Xcnos from their bodies. 1 Such did not appear to be 

 the case here, for one wasp which was actively feeding upon the 

 nectary of a cotton square late in the afternoon (the males almost 

 always leave the pupa case early in the morning), proved on 

 later examination to bear ten empty male pupa cases between 

 the segments of the abdomen. In some of the wasps included 

 in the table it is quite possible that a number of the males may 

 have emerged at time of capture or during the several hours con- 

 finement of the wasps in a screen box before careful examination. 

 It has been remarked by Packard that the males are apt to emerge 

 during any excitement or great muscular exertion of the host, for 

 example when the wasp is caught in a net. This may to some 



1 In this connection it is interesting to note that this fact was commented upon in 

 1793 by Rossi in what is no doubt the first mention of Xenos in scientific literature. 

 His statement given in the Bulletin de la Societe Philomathique, Vol. i, p. 49, is as 

 follows : " Get insecte habite a 1'etat de larve et de chrysalide dans la guepe fran- 

 caise vespa gallica C'est sous la quatrieme anneau de 1' abdomen de cette guepe que 

 se trouve sa chrysalide ; sa presence ne nuit pas a la vie de la guepe, et on rencontre 

 souvent sous les anneaux de leur abdomen les chrysalides dont 1'insecte est sorti, sans 

 que les guepes paroissent incornmodees. " 



