THE GENETICS OF HABROBRACON JUGLANDIS ASHMEAD 



made from 20° C. to 30° C. or 35° C. This is 

 probably to be explained by a differential le- 

 thal effect on males in general. At all temper- 

 atures percentages of males among biparentals 

 change significantly v/ith increasing age of 

 mothers. An experiment in which eggs were count- 

 ed showed that at the higher temperature the 

 percentage of eggs producing impaternate males 

 was decreased. Among biparental offspring males 

 were increased and females correspondingly de- 

 creased.. The conclusion is drawn that increased 

 temperature increases mortality of males and 

 favors homeosyngamy (male-producing combina- 

 tions) at the expense of heterosyngamy (female- 

 producing) (Anderson, 1935, 1936). On the whole, 

 however, sex ratio is less dependent upon tem- 

 perature than is fecundity. 



High temperature may cause or, at least, 

 bring to light, various mutations. The mutant, 

 shot-veins, a semidominant factor, appeared ac- 

 cidentally. It arose simultaneously in three 

 different lines after extreme heat treatment of 

 larvae. It causes veins of the wings to be bro- 

 ken up and distorted. The trait proved to be 

 hereditary, and shot-veins is fully fertile and 

 stable . 



A number of mutations have occurred following 

 X-radiation in Habrobracon. Treatment is given 

 at various stages, to eggs in the mother before 

 they are laid, to eggs after laying, to larvae, 

 to pupae, and to sperms in the adult male before 

 mating. The offspring of the treated wasps are 

 examined, and the un.isual individuals are al- 

 lov/ed to produce progeny to show v/hether or not. 

 the questionable traits are hereditary. 



Unlaid eggs of Habrobracon are most sensi- 



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