WALNUT APHIDES IN CALIFORNIA. 35 



Key to the Species of Aphidid^e Known to Occur on Walnut in California. 



A. Cornicles quite evident, about as wide as long. 



Chroma-phis juglandieola Kalt. 

 AA. Cornicles barely perceptible, considerably wider than long. 

 B. Tibiae of winged viviparous female entirely dusky. 



Monellia californica Essig. 

 BB. Tibiae of winged viviparous female for the most part pale. 



C. Filament of joint VI longer than joint VI ; oviparous female with 



four longitudinal rows of. capitate hairs Monellia caryse Monell. 



CC. Filament of joint VI shorter than joint VI; oviparous female with 

 six longitudinal rows of capitate hairs Monellia earyella Fitch. 



NATURAL CONTROL OF WALNUT APHIDES. 



INTERNAL PARASITES. 



In July, 1912, a small chalcidid wasp was observed ovipositing in 

 a pupa of Monellia caryse. This is the only record of parasitism or 

 attempted parasitism observed during two seasons, so there is good 

 reason to believe that these aphides are practically immune from the 

 attacks of internal parasites. 



FUNGOUS DISEASES. 



Although occasionally a plant-louse may be noticed here and there 

 killed by fungus, only a single instance of the destruction of a colony 

 by this agency came under the writer's notice. This occurred on 

 May 20, 1911, following a rainstorm, and all the plant-lice on a few 

 leaves were destroyed. The disease did not spread far, some cause 

 or other checking the fungus shortly after its appearance. 



PREDACEOUS ENEMIES. 



Predaceous enemies are of prime importance in the control of 

 plant-lice on walnuts and where the aphides occur in any numbers 

 may always be found preying on them from June to September. 

 Unfortunately they do not make their appearance on the walnuts 

 until their prey has had time to do much damage to young nuts and 

 to become abundant enough to cause collective injury to the tree. 

 Should these predaceous forms appear in early spring they would 

 quickly wipe out the few plant-lice present at that time and conse- 

 quently their progeny would starve to death. As injury is thus done 

 to the nuts and to the vitality of the tree before the advent of natural 

 enemies, artificial measures must be practiced in order to insure 

 healthy trees and perfect nut crops. 



The predaceous enemies of walnut plant-lice include syrphus-fly 

 larvae, agromyzid larvae, chrysopid and hemerobid larvae, coccinellid 

 beetles and their larvae, CamptobrocMs brevis Uhler (Heteroptera) and 

 its larva, and various spiders. 



