SEX-DETERMINATION OF HADROBRACON BREVICORNIS. 25! 



millimeters in length, but minute individuals occur as well. The 

 latter are probably starved. They are fertile, nevertheless, and 

 give rise, when bred, to wasps of normal size. 



A 



FIG. i. 



The insects mate readily as soon as they emerge from their 

 white silken cocoons. The females deposit their eggs upon the 

 bodies of full-grown caterpillars of the Mediterranean flour-moth, 

 Ephestia kuehniella Zeller, and probably also upon other meal 

 caterpillars. The caterpillars are stupefied by the sting of the 

 wasps and remain quiet until the acephalous, apodous larvae 

 emerge and devour them. Several eggs are laid upon one cater- 

 pillar and as many as ten or a dozen wasps will sometimes de- 

 velop. Usually the number is smaller. At a high temperature 

 the length of a generation is ten days or less. The adult females 

 may live as long as six weeks. 



The work has been handicapped by lack of sufficient cater- 

 pillars at necessary times. As a consequence I have not been 

 able to rear as many offspring as desired. The greatest number 

 of progeny obtained from a single female was one hundred and 

 twenty-eight, but I am convinced that many more could be 

 secured if sufficient food were available. The technique of 

 rearing and handling the moths is being developed and it is 

 hoped that further work upon the wasps may be done as a result. 



A protozoan parasite has been found in the caterpillars and in 

 Hadrobracon. It has been eliminated by heat sterilization of the 

 food and glassware. Its life history is being worked out by Dr. 

 D. H. Wenrich. The small numbers in some of the families of 

 Hadrobracon are due to the presence of this parasite. 



My thanks are due to Dr. McClung for the facilities of the 



