16 NEW CALIFORNIAN APHIDIDAE 



Aphis senecio new species (Figs. 6, 12, 21, 24.) 



This is a very common species throughout central and south- 

 ern CaKfornia, and has been reported several times as Aphis 

 hakeri Cowen.^ Davidson's description of Aphis sp. (1909) prob- 

 ably is also of this species. Concerning this Davidson writes: 

 "I think the species on Senecio mikanioides was the same as on 

 the other plants, but there might have been more than one species 

 on the host." Although this species was considered for a long 

 time to be Aphis hakeri Cowen, the fact that it was never found 

 on apple or other deciduous trees where A. hakeri is supposed to 

 pass the winter, as well as the fact that it never seemed to have 

 any particular liking for clover, on which A. hakeri is described 

 as being a considerable pest, led the writer to believe that it was 

 not this species, but some other. Davidson writes that he has 

 noticed this and is of the same opinion. Morrison was also 

 doubtful, although neither he nor Davis were able to detect any 

 structural differences. Gillette stated that he has specimens 

 from Davidson, and that he does not consider it to be Aphis 

 hakeri Cowen, as it differs particularly in habits, and structurally 

 in the length of the beak. Below is an extract from a letter 

 from Davidson concerning this species. 



"Williams' Aphis senecioms appears to be closely related but 

 is obvaously different in the sensoriation and other points. None 

 of Williams' other Compositae species appear to approach this 

 species. The first host upon which I took it was the common 

 groundsel, which, I believe, is an imported European species. 

 This might point to its occurrence in Europe, but I am unable 

 to fit it to any European species. I think you are justified in 

 giving it a name, as no American aphidologist has been able to 

 determine it for surety." 



The species has been taken throughout the San Francisco 

 Bay region and throughout southern California on a large num- 

 ber of host plants, particularly Compositae. At present there 

 are about twenty-two host plants, belonging to sixteen genera 



^Davidson, W. M., Notes on the Aptiididae Collected in the Vicinity of 

 Stanford University, Jour. Econ. Ent., 2: 302, 1909, Aphis sp., desc; David- 

 son, W. M., Further Notes on the Aphididae Collected in the Vicinity of Stan- 

 ford University, Jour. Econ. Ent., 3: 377, 1910, A. hakeri Cowen (?), list; 

 Davidson, W. M., Plant Louse Notes from California, Jour. Econ Ent., 7: 

 133, 1914, A. hakeri Cowen, list; Essig, E. O., Insects of California, Cal. Com. 

 Hort., 87, 1915, A. hakeri Cowen, list. 



