THE PLUM PLANT-LOUSE. 



(Myzus mahaleb Fonsc. ) 

 By Theodore Pergande. 



Several species of plaut-lice occur upon the plum, aud one of these is 

 so much like Phorodon humuli, the hop plant-louse, in certain stages of 

 its development that without great care the observer will be led astray. 

 Its habits are different, and it never migrates to the hop. This species 

 is Myzus mahaleb Fonscolombe. It was formerly considered as a true 

 Phorodon, and is quite generally mentioned in literature under this 

 genus. On account of the confusion liable to arise, we may devote 

 some little space to a consideration of this species. The generic char- 

 acters separating Myzus from Phorodon are as follows : 



Frontal tubercles prolonged at inner angle into a prominent, slender, por- 



rected tooth ; first antennal joint bluntly but distinctly gibbous Phorodon. 



Frontal tubercles gibbous at inner angle; first antennal joint without a 



tooth Myzus. 



In P. liumuli the inner apical angle of the frontal tubercles is pro- 

 longed into a rather long and slender branch, reaching in the apterous 

 females, larvae, and pupae, except those of the first generation, to about 

 the apex of the first antennal joint, being somewhat shorter, though still 

 slender, in the winged form, and having a distinct, stout, and blunt 

 tubercle near the inner apical angle of the first antennal joint. In M. 

 mahaleb, however, the inner prolongation of the frontal tubercles is 

 rather insignificant, stout, and rounded, and the tooth of the first joint 

 is wanting in all generations. The only generation in which both spe- 

 cies are difficult to be separated is the first, in which the frontal tuber- 

 cles in both species are scarcely indicated, whereas in the last or sexual 

 generation the females of both may be separated without difficulty. 



The synonymy of the species is as follows : 



Myzus mahaleb Fonsc. 



Aphis pruni- mahaleb Fonscolombe, Ann. Soc. Ent. de France, X, 1841, p. 175. 



Aphis mahaleb Koch, Pflanzenlause, 1857, p. 113. 



Myzus mahaleb Passerini, Aphididte Italicae, 1863, p. 26. 



Phorodon humuli var. malaheb Buckton, British 'Aphides, 1876, p. 168. 



Phorodon humuli var. mahaleb, Thomas, Nox. and Benef. Ins. 111., 1878, p. 72. 



Siphonophora achyrantes Monell (?), Nox. and Benef. Ins. 111., 1878, p. 187. 



Regarding the synonomy of this species much uncertainty has previ- 

 ously existed. Notwithstanding that Fonscolombe and Koch have indi- 

 cated its specific characters and Passerini its generic position, it is still 



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