THE GENETICS OF HABROBRACON JUGLANDIS ASHMEAD 



thals at stronger dosages, and partial sperii 

 inactivation at very high dosages. 



Treatment of Habrobracon larvae with X-rays 

 was begun in January 1929. Progeny from crosses 

 of different stocks were used with pure stocks 

 sometimes treated as checks. Treatments ranging 

 from 730 to 4378 R units were given. No treat- 

 ment had complete lethal or sterilizing effect, 

 although the highest dosage approached this. 

 Younger larvae were found to be more susceptible 

 to X-radiation than older, and male larvae more 

 susceptible than female larvae. Irradiation 

 tended to kill the younger larvae immediately 

 while the older ones continued development and 

 often died after metamorphosis and before ec- 

 losion (A. R. Whiting and Bostian, 1931). 



There have been some fifty mutant types de- 

 rived from X-ray experiments on Habrobracon, 

 Dosages of 2,000 to 5,000 R units have produced 

 the majority of these mutations. After 10,000 R 

 units there is a dominant lethal change of some 

 sort produced in practically every sperm cell. 

 Dosage for egg cells must be much higher for the 

 chromosomes are not so closely packed together 

 and apparently the closer the packing the better 

 chance for irregular recombinations. Table III 

 has been prepared to summarize the effect of 

 •various dosages of X-rays on eggs, sperm, and 

 larvae. Considerable experimentation is still 

 being carried on along this line, and various 

 dosages of X-rays are now being combined with 

 treatment at various degrees of temperature. 



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