June, 1922 bionomics of alphelinus semiflavus 



225 



were encountered but one other time, when three were taken 

 from Cage 48a3 on March 2, 1921. One of these was confined 

 with females among some aphids on a dock leaf in a small vial, 

 and copulation was observed. No observations were made on 

 mated females to determine whether mating had any effect on 

 the proportion of sexes and number of offspring produced. This 

 must be left for later investigation. 



Table IV. 



Sample Counts from a Series of Partheno gene tic Generations Showing Proportion 



of Sexes. 



Some of the Encyrtidae, a family of scale parasites, closely 

 related to the Eulophidae, produce but few males or none at all. 

 In other species of the genus Aphelinus, feeding on aphids, the 

 males are not known. 



The production of females parthenogentically that are 

 capable of producing more females in the same manner, for an 

 indefinite number of generations, is a very valuable asset to a 

 parasite when it is to be established in new territory. By this 

 method of reproduction the chances of its increase are greatly 

 enhanced. Likewise, it is less liable to die out through reduction 

 in numbers and consequent scattering of individuals that 

 would reduce the chances of mating where this was important 

 for the perpetuation of the race. 



The Egg. 



Description. — The egg is elongate ovate, and slightly bent 

 in the middle, with dimensions of .21 x .05 mm. The anterior 

 end is slightly more rounded than the posterior, which tapers 

 bluntly to a point. At the anterior end, there also appears a 

 small nipple-like micropyle that projects just far enough from 

 the surface to be seen with a high power compound microscope. 

 The color, in reflected light, is a very light cream-white; darker 



