June, 1922 bionomics of alphelinus semiflavus 



231 



Effect of Host on Parasite. 



As in common with most parasitic Hymenoptera, there is a 

 great variation in size of adults according to food supply or 

 size of host. This was more than double in Aphelinus, or from 

 .35 mm. to .75 mm. in length. The extremely small specimens 

 were apparently sterile, for several trials on parasite-free 

 nymphs failed to get them to reproduce, or even lay eggs. An 

 attempt at oviposition was noticed in one case, but the parasite 

 was unable to extrude the ovipositor its full length. 



Fig. 2. A series of curves shoiving the effect of the parasite Aphelinus semiflavus 

 on the production of young in adult viviparous Myzus persicce. a. Average daily pro- 

 duction of young in six females for the average total period of production, with 

 Aphelinus but unparasitized (note drop in curve between x and xi when parasites 

 were introduced, showing effect of the presence of Aphelitius on production of 

 young); b. average daily production of young in ten females for the average total 

 period of production with Aphelinus but unparasitized. (note drop between x 

 and xi as in a); c. average daily production of young in ten females free from par- 

 asites; d. average daily production of young in two females for the average total 

 period of production before and after parasitism. The parasites were introduced 

 at the point x and removed at Xi. Death from parasitism occurred at the end of 

 he curve. 



