WALNUT APHIDES IN CALIFORNIA. 6 



ceptible, yellow; tail not present. Legs pale; the spots on the apex of the hind 

 femora are larger than those of the wingless. In well-colored examples such spots 

 occur on the middle femora and those on the hind femora are enlarged into a ring. 

 The wings are transparent; the stigma yellow, cubitus and the two inner veins brown 

 and markedly stouter at the base, then gradually becoming finer and paler; veins of 

 lower wing and wing margin pale yellow; stigmatic or fourth vein very fine and 

 strongly curved. 



There is no doubt that Kaltenbach's species is the same that 

 occurs commonly all over California on the European walnut. The 

 black femoral spot, together with the antennae as described, estab- 

 lishes its identity. Kaltenbach's wingless form appears to be the 

 oviparous female in her penultimate molt, for the true apterous vivip- 

 arous female — a common form in the majority of plant lice — does 

 not exist, or, if it does, is extremely rare, the author in two years of 

 close observation having failed to observe it. Buckton (1872) 1 

 gives a description of the apterous viviparous form, but he also seems 

 to have had before him the immature oviparous form. 



The insect probably occurs wherever the European walnut is 

 grown. It has been reported from all over Europe, as well as from 

 the States of Colorado (Gillette, 1910), Oregon (Wilson and Lovett, 

 1911-12), and California (Essig, 1909). 



GENERAL DESCRIPTION; CHARACTER AND EXTENT OF INJURY. 



This aphidid is a small, lemon-yellow insect, about one-sixteenth 

 of an inch in length. It occurs sporadically on the underside of the 

 leaves and on the young fruit of the European walnut (Juglans regia) 

 and its cultivated forms and hybrids. It appears on the upper sur- 

 face of the leaf only at times of very severe infestation. It is to be 

 found from late February or early March until December, persisting 

 as long as the leaves remain on the tree, but is present in greatest 

 numbers during the months of July and August. As many as 200 

 individuals may occur on a single large leaflet if infestation be severe, 

 while the author has observed over 30 aphides on a single young nut. 

 Nuts badly infested while young never attain their normal size. 

 Many of them mature half-sized, covered on the upper surface with 

 the black sooty fungus which thrives on the sticky exudations of the 

 aphides. Attacks on the tree year by year also materially reduce 

 its vitality, since the aphides will be present in the spring even before 

 the leaves have opened and will remain until these drop. 



Plate I, figure 1, shows the difference in size between infested and 

 uninfested nuts of one variety of European walnut, while Plate I, 

 figure 2, demonstrates the appearance of the sooty fungus on a 

 walnut leaf. 



1 Dates in parentheses refer to the Bibliography, p. 47. 



