WALNUT APHIDES IN CALIFORNIA. 27 



narrowed and elongated. The antennae are longer than the body, tapering, seven- 

 jointed; two basal joints as broad as long, twice the diameter of the following joints; 

 third joint longest, slightly thicker towards its base; fourth and fifth joints rathershorter 

 than the third, cylindric; two last joints together about equalling the fifth in length ; 

 the sixth swelled at its tip into a long oval knob, the seventh more slender but not 

 capillary, shorter than the sixth; a broad black band at the base of the third and each 

 of the following joints. First vein of the fore wings straight and almost transverse; 

 second vein bent near its base, running first towards the apex and then turning rather 

 abruptly and continuing straight to the inner margin, more than twice as far from the 

 first at tip as base; third vein arising from the stigma near its anterior end, and not 

 from the rib-vein forward of the stigma, as it does in the aphides generally, except 

 those pertaining to this group, its base and its apex about the same distance from the 

 second vein that this is from the first, forking rather forward of its middle, strongly 

 bent at this point, and from hence to its tip parallel with the third vein or but slightly 

 diverging from it, its tip a third nearer that of the third vein than this is to the second; 

 second fork nearer the fourth vein at tip than to the first fork, the triangular cell be- 

 tween it and the first fork with its three sides equal; fourth vein short and often nearly 

 abortive, shorter than the second fork, equally curved through its whole length, its 

 tip much nearer that of the rib-vein than that of the second fork; rib-vein very slightly 

 diverging from the margin from the base to the stigma, curved from thence to its tip. 

 Stigma oval, about twice as long as wide, watery, sometimes tinged with yellowish. A 

 variety has the stigma dusky at its tip. Another variety (costalis) has the rib-vein 

 coal black interrupted with whitish towards the stigma, which is dusky and black at 

 each end. 



In a general discussion of this species before his description Fitch 

 refers to the minute cornicles characteristic of this and kindred 

 species. In his third report on the insects of New York he mentions 

 the European walnut aphis and says "European O. juglandicola of 

 Koch" [Chromaphis juglandicola Kelt.] "appears closely related to 

 this present species" [i. e. Callipterus caryellus]. Fitch gave the 

 host plant of his species as the hickory. Oestlund (1887) reports it 

 inMinnesota from Caryaamara'Nutt. Davis (1910) and other Eastern 

 writers record it from hickory in the Eastern States. In California 

 the normal food plants are the California black walnut (Juglans 

 californica) and hybrids derived from this tree. 



GENERAL APPEARANCE; CHARACTER AND EXTENT OF INJURY. 



In general appearance this aphis is very similar to the American 

 walnut aphis (Monellia caryx Monell) and can not be distinguished 

 from it except when viewed under the microscope or a powerful hand 

 magnifier. Its habits of life and the character and extent of its 

 injury are also very similar to those of M. caryx. The writer had 

 observed this aphis for several months before he realized that it was a 

 distinct species and not a variety of caryse, as he had previously 

 supposed. When the sexed forms appeared it was noticed that the 

 oviparous* female of caryella differed markedly from the same form 

 of caryse, and this led to a closer scrutiny of the viviparous form 

 resulting in the establishment of the points of divergence shown in 

 Table VIII. 



