WALNUT APHIDES IN CALIFORNIA. 35 
Key to the Species or Aphidid^e Known to Occur on Walnut in California. 
A. Cornicles quite evident, about as wide as long. 
Chroma-phis juglandicola 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, CamptobrocJiis brevis Uhler (Heteroptera) and 
its larva, and various spiders. 
