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



COHOSTS. 



Previous records give Myzus persicce Sulz., Aphis gossypii{?) 

 Glover, Aphis maidis Fitch, and Chaitophorus viminalis Mon., 

 as hosts for Aphelinus semiflaviis . The writer can add to this 

 list from his own rearings, the following: Macrosiphum pisi 

 Kalt., M. granarium Kirby, M. Sanborni Gillett, rarely, and 

 Anur aphis viburnicola Gillett. 



Myzus persicce, from which most of the field records come, 

 seems to be the preferred host, although it took to Macrosiphum 

 granarium and Anuraphis viburnicola quite as readily in cap- 

 tivity. Macrosiphum pisi was not parasitized very heavily, due, 

 perhaps to its long legs and large size, and irritability. Macro- 

 siphum sanborni escaped almost entirely for no apparent reason. 

 They were only rarely attacked even when confined in a cage 

 with a number of parasites, and a colony went through the 

 winter in the greenhouse among many parasites with but a 

 scarce eight or ten being parasitized. 



Several attempts were made to rear Aphelinus in Aphis 

 rumicis, another common dock aphid, but all were unsuccessful. 

 The parasite would oviposit in them freely, and subsequent 

 dissection showed that the eggs would hatch and the larva 

 become nearly half grown, in some cases; but they would always 

 die before reaching maturity. In most cases death occurred 

 shortly after the egg hatched. 



INTERRELATIONS WITH APHIDIUS. 



Considerable importance has been attached to the inter- 

 relations of primary parasites in a single host, since the dis- 

 covery by Pemberton and Willard (18) of the disastrous results 

 of the interrelations of two primary fruit fly parasites imported 

 to the Hawaiian Islands. 



From what is known of the two groups of primary aphid 

 parasites, there seems to be no question about the superiority 

 of Aphidius over Aphelinus as a controlling factor for aphids. 

 It not only appears earlier in the season, but lays more eggs in 

 a shorter time, is more vigorous in its actions, is not confined so 

 closely to the younger aphids, and has a much greater dispersal 

 than Aphelinus. It was, therefore, both interesting and 

 important to determine to what extent these two occurred in 

 the same host, and the ultimate outcome of such occurrence. 



