82 INJURIOUS AND BENEFICIAL INSECTS OP CALIFORNIA. 



THE WALNUT PLANT LOUSE 53 



Chromaphis juglandicola (Kaltenbach) 



(Lachnus juglandicola Kaltenbach) 



(Fig. 65) 



Description.— The presence of this plant louse is usually manifested 

 by the smutting of the walnut trees during the early summer months. 

 Close examination, especially of the undersides of the leaves will 

 reveal the minute, light yellow aphids. When magnified the winged 

 individuals will be found to have black markings on the antennae, the 

 middle and hind femora, and on the abdomen. The true sexual, 

 wingless females have two distinct broad black bands across the 

 body. The eggs are shiny black, oval and very small. 



Fig. 65. — The walnut plant louse, Chromaphis jxiglandicola (Kalt.). Winged agamic 

 female to left and nymph of same to right, apterous sexual female in middle. Greatly- 

 enlarged. (Author's illustration, P. C. Jr. Ent. ) 



Life History. — The sexual females deposit eggs upon the branches 

 in the fall. These hatch in the spring (February and March) and give 

 rise to great numbers of young which follow. The growing lice excrete a 

 large amount of honey-dew which covers the foliage and ground 

 beneath the tree. This honey-dew is responsible for the smutting 

 which is sure to appear wherever the attacks occur. Late in July 

 and in August the numbers gradually diminish and when the leaves 

 begin to fall only the freshly laid eggs remain upon the branches. 



Nature of Work.— The plant lice settle upon the first tender shoots 

 and later upon the undersides of the leaves which are occasionally 

 slightly curled. They also attack the young nuts. All secrete quan- 

 tities of honey-dew which covers the trees and upon which a black 



5S Key to the species of aphids attacking walnut trees in California. (From W. M. 

 Davidson, Bui. No. 100, U. S. Dept. Agric, Aug. 31, 1914). 



a. Cornicles quite evident, about as wide 



as long Chromaphis juglandicola (Kalt.) 



Cornicles barely perceptible, considerably wider than long b 



b. Tibiae of winged viviparous female entirely 



dusky Callipterus californicus Essig 



Tibia? of the winged viviparous female for the most part pale c 



c. Filament of joint VI longer than joint VI ; 



oviparous female with four longitudinal 



rows of capitate hairs Callipterus cargo: (Monell) 



Filament of joint VI shorter than joint VI ; 

 oviparous female with six longitudinal rows 



of capitate hairs Monellia caryella (Fitch) 



The little hickory aphis, Monellia caryella (Fitch) occurs in the central part of the 

 State. It attacks the California black walnut (Juglans calif ornica), hickory, bitter- 

 nut (Gary a cordiformis) . 



The American walnut aphis. Callipterus carym (Monell) has been collected in the 

 central part of the State by Mr. Davidson and is recorded as attacking the eastern 

 black walnut (Juglans nigra), hickory and pecan. 



(Neither californicus nor caryw can rightfully be placed .in the genus Monellia. 

 See footnote 54). 



