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 winch 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 larvae 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 1 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 



iBul. 176, Cornell Agr. Exp. Sta., p. 180. 



