224 E. A. HARTLEY Vol. XXII, No. 8 



remains slumped down apparently oblivious to the slow ebbing 

 away of its life blood, the only movement being a slight wave 

 of a leg or antenna. 



Length of Adult Stage. 



The length of life in the adult has been observed to vary 

 according to the kind of food available. Temperature also is 

 undoubtedly an important factor, but no accurate experiments 

 have been attempted to show how it operates. 



The effect of the different kinds of food on the length of life 

 is shown in Table III, and may be briefly summarized as 

 follows: Confined without food, on plants alone, among older 

 aphids on plants, or in small receptacles, death ensues in less 

 than four days; on honey dew they live for twelve days; and 

 one specimen was kept alive for thirty-nine days on honey solu- 

 tion in distilled water, given fresh every day until it finally 

 escaped. There is reason to believe that they will live much 

 longer on this. The only one carried through to normal death 

 on aphids, lived thirty-six days; producing eggs for thirty of 

 these days. 



REPRODUCTION AND DEVELOPMENT. 



Method. 



The prevailing method of reproduction in Aphelinus semi- 

 flavus, as well as in a number of other chalcid parasites, is by 

 parthenogenesis. Seventeen successive generations have thus 

 far been reared parthenogenetically, and there is every reason 

 to expect many more to follow indefinitely; since the last 

 offspring appear as vigorous as the first. 



Proportion of Sexes. 



Males are quite rare in this species. Out of more than 900 

 individuals examined from the different generations through- 

 out the series of parthenogenetic generations, but seven males 

 were found. These were scattered more or less irregularly 

 through the series as shown in Table IV. It is quite possible 

 that males might have appeared from time to time in other 

 rearings and passed unnoticed, due to the difficulty of dis- 

 tinguishing the sexes without a microscope. However, through- 

 out all the observations, of either living or dead material, males 



