68 DECIDUOUS FRUIT INSECTS AND INSECTICIDES. 
the only places where the peach borer has become a pest. Other 
peach, apricot, and plum sections in the Napa, Sonoma, Suisun, and 
San Joaquin Valleys and on the western slopes of the Sierra Nevada 
Mountains are not troubled at all. 
VARIETIES OF CULTIVATED FRUITS ATTACKED; RESISTANT BUDDING 
AND GRAFTING STOCKS; SOIL CONDITIONS AS BEARING ON INFESTA- 
TION. 
The peach borer is eminently a root-boring pest, and two factors, 
therefore—the kind of root stocks upon which the trees are growing, 
and the nature of the soil—determine largely the amount of damage 
that the borers will inflict. Peach and apricot stocks are most sus- 
ceptible to attack, although almond, cherry, apple, and native plums 
are less so; and the wild plum, known as the Myrobalan or cherry 
plum (Prunus cerasifera) is almost entirely exempt. Myrobalan 
plum seedlings are imported in great quantities from Europe and they 
are now recognized as one of the best stocks upon which to graft 
domestic plums. This stock is especially susceptible to attack only 
when a tree has been weakened by some cause such as a lack of water 
or cultivation or when it has been partly killed by ‘‘ gophers” or other 
rodents. Almond stocks are more or less resistant if planted in soils 
suitable to their growth. Borers appear to attack trees more readily 
when they are planted in soils of a light sandy or gravelly texture. 
The writer does not believe that newly hatched larve can reach 
the lower crowns or roots more easily in light than in the heavy soils 
of loam or clay; it appears, rather, that the trees themselves are not 
so strong and are therefore not so resistant. 
DESCRIPTIONS, SEASONAL HISTORY, AND HABITS. 
THE EGG. 
DESCRIPTION. 
The egg of the California peach borer measures approximately 
0.72 mm. in length and 0.44 mm. in width. It is flattened and 
depressed on the sides and is depressed at one end. The eggs are 
chestnut to dark-brown in color and when magnified the outer surface 
has a stippled and mosaic appearance. The sculpturing so character- 
istic of the eggs of the eastern peach borer‘ is also apparent on the 
eggs of the California peach borer (Sanninoidea opalescens). 
DEVELOPMENT AND HATCHING. 
The writer was able to make constant and daily observations on 
oviposition by moths which were confined in out-of-door rearing 
cages built over small apricot and peach trees in the back yard of the 
1 Bul. 176, Cornell Agr. Exp. Sta., p. 180. 
