Chapter IX 

 ENVIRONMENTAL EFFECTS 



It has been found that in Habrobracon ju- 

 glandis,asin other experimental animals, cer- 

 tain environmental factors have marked effects 

 upon the appearance, fecundity, and behavior of 

 the animal. The nature of mutations and the 

 rate of their occurrence are also affected. In- 

 vestigation of various factors and their effects 

 is at present in progress. Temperature, humid- 

 ity, and X-radiation, have been found to be im- 

 portant in developmental studies. 



Ever since Habrobracon has been reared in the 

 laboratory, the degree of temperature has been 

 known to determine body color, to affect repro- 

 duction, to affect the production of mosaics, 

 and to cause mutations. Wild-type individuals 

 vary from honey-yellow to almost black, higher 

 temperatures producing more yellow pigment , low- 

 er more black. Heredity plays some part, for 

 races under constant temperature differ con- 

 sistently in pigmentation. 



Schlottke (1926) from a carefully planned and 

 controlled study of temperature and pigment in- 

 terrelationships in wild-type Habrobracon draws 

 the following conclusions: (1) deposition of 

 pigment (black) decreases linearly with rising 

 temperature; males are on the average, darker 

 than females, (2) pigment is deposited especial- 



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