THE GENETICS OF HABROBRACON JUGLANDIS ASHMEAD 



of an inch above a mirror. Then by focusing 

 either upon the insect directly or' upon the 

 image, upper or lower sides may be observed. 

 There is no danger of contamination from the 

 food even if wasps have infested the caterpil- 

 lar culture for eggs are never laid except upon 

 torpid and flaccid hosts. Such should, of 

 course, be discarded in selecting caterpillars) 

 for the culture vials. 



An occasional female lays many sterile ova. 

 Data on eggs of such exceptional females are 

 not included in general summaries. There is' 

 likewise a tendency on the part of many females* 

 to lay "shells," apparently filled only with 

 fluid. This soon evaporates, and the egg be- 

 comes brittle. In one series (A. R. Whiting, 

 1940a) the percentage of such "shells" was 2.26' 

 for the first ten days of life of the females^ 

 and 12.06 for the second ten days. Some females^ 

 produced no "shells," although all were from 

 the same inbred line. Those "shells" are like- 

 wise omitted in computing hatchability ratios. 

 It has been thought that the "shells" might be 

 the result of the females stinging their eggs. 

 It has been concluded that females sting eggst 

 very rarely if at all, and that stung eggs can 

 continue develooment after such injury. In or- 

 der to determine the time of death of eggsi 

 which, for various reasons, do not hatch, the 

 eggs may be collected at intervals and placed 

 in the mineral oil, "Nujol," where development 

 proceeds normally and conditions can be clearly 

 observed. 



The developmental limits for the egg have 

 been found to be 12-38° C. at a relative humid- 

 ity of 76-98 per cent (Maercks, 1933). The 



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