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THE CANADIAN ENTOMOLOGIST 



quite a different species, a typical Myzus. This species will be discussed in a 

 following paragraph. 



M. ribiellum (fig. 5) seems to be quite different from any previously de- 

 scribed species occurring on Rihes. It is not a typical Macrosiphum but probably 

 can best be placed in that genus. From other species occurring on Ribes it 

 may be separated as follows. The slightly swollen cornicles and fewer sensoria 

 on antennal segment III of the apterous distinguishes it from Macrosiphum 

 lactuccB Schr. We are not familiar with M. rihicola Kalt., but Theobald gives 

 it as a synonym of M. lactuccB Schr. Rhopalosiphum lactucce Kalt. has much 

 greater swollen cornicles which are conspicuously club shaped. Whether 

 R. sonchi Oestl. is a synonym of lactucce Kalt. is questionable in my mind. In 

 examining specimens which appear to be typical sonchi collected on Sonchiis 

 and typical lactuccB collected on Ribes, I can make out no constant character to 

 distinguish the two except that the filament of antennal segment VI in all my 

 sonchi specimens is approximately one half longer than segment III, while in 



Fig. 30. — Macrosiphum ribiellum. n.sp. — A. cornicle of apterous viviparous female; B, antennal hair; C, antennal 

 segments III and IV of winged viviparous female; D, antennal segments III and IV of apterous viviparous female. 



lactucce filament of VI is only very slightly (1/7 to 1/6) longer. Rhopalosiphum 

 brittenii Theob. has large swollen cornicles like lactucce which at once separates 

 this species. Myzus ribis L. bears numerous sensoria on IV and V, and has 

 very slender cylindrical cornicles which easily separate it from Macro, ribiellum. 

 Myzus whitei Theob. is separated by the occurrence of a number of sensoria 

 on IV and V, but resembles ribiellum in the character of the cornicles. Myzus 

 dispar Patch also resembles ribiellum in the character of the cornicles, but 

 dispar differs by having antennal segment VI filament twice the length of seg- 

 ment III. We have not seen Rhop. ribesina v. d. G., but the cornicles are said 

 to be distinctly club-shaped and the antennae to bear sensoria (10-15) on antennal 

 segment IV. Myzus cynosbati Oestl. and M. houghtonensis Troop have more 

 sensoria on segment IV and the cornicles are short, cylindrical and typical of 

 many species of the genus Myzus. Aphis (Myzus) neomexicanus Ckll. is 

 characterized by antennae much shorter than body, cylindrical cornicles which 

 do not reach tip of abdomen, and by black markings on abdomen of winged 

 female. Myzus ribifolU Davidson is readily separated by the cornicles which 

 are typically Myzus. 



