SEX-DETERMINATION AND BIOLOGY OF A PARA- 

 SITIC WASP, HADROBRACON BREVICORNIS 



(WESMAEL). 



P. W. WHITING, 

 UNIVERSITY OF PENNSYLVANIA, PHILADELPHIA, PA. 



The problem of sex-determination is nowhere of greater interest 

 than in the Hymenoptera. The occurrence of parthenogenesis 

 as well as sexual reproduction adds interest to this matter, 

 especially in view of the fact that considerable variation in con- 

 ditions obtains, not only between the different families, but even 

 between the' minor groups of the same family. 



The present studies deal with an insect, Hadrobracon brevi- 

 cornis (Wesmael), belonging to the family Braconidse. 



The insects vary greatly in coloration, ranging from near black 

 though various intermediate patterns to near yellow. In the 

 near-yellow individuals black pigment usually persists in the 

 antennae, in the compound eyes, about the ocelli, and in small 

 markings near the base of the wings. No experiments have been 

 made to test the cause of color variation except that it has been 

 shown that it does not yield to selection. It seems probable, 

 therefore, that it is due to some environmental influence. It 

 shows a certain correlation with size, for the dwarfed specimens 

 are usually very dark while the larger individuals are either very 

 light or of intermediate color. There is no apparent correlation 

 of color with sex. 



In view of the fact that genetic differences with respect to 

 color exist in the honey-bee, I had expected the yellow and the 

 black variations of Hadrobracon to reproduce themselves, but 

 this is not the case. 



Fig. i, A, shows a light colored male and Fig. I, B, shows a 

 rather dark female. Sexual dimorphism is evident in the longer 

 antennae of the male and in the presence of the ovipositor of the 

 female. Variation occurs in the number of antennal joints and 

 in the general body size. The larger specimens are three to four 



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