68 DECIDUOUS FKUIT INSECTS AND INSECTICIDES. 



NATURE OF INJURY. 



The larvae upon hatching soon bore into the fleshy hull covering 

 the walnut proper. Some individual larvse one- fourth grown were 

 found feeding in this hull, some burrowing around through the 

 fleshy part, and others tunneling back and forth on the inner surface 

 next to the walnut shell, producing many little narrow furrows along 

 this inner surface. The majority of the larvse, however, go at once 

 into the nut, entering always through the fibrous tissue connecting 

 the halves of the shell at the base or the stem end. The larva? may 

 bore into the lobes of the kernel or feed on its surface. Some eat over 

 a large portion next to the shell, some follow along the central area, 

 while others may spend all the time near the entrance, eating away 

 a larger portion of the kernel at this place. In any case the entire ker- 

 nel is rendered rancid and unsuited for human consumption. Plate 

 VII, figure 1, shows characteristic injury to the walnuts and Plate 

 VII, figure 2, a larva at work in the kernel, the latter twice enlarged. 



EXTENT OF INFESTATION. 



Extended search throughout the central part of Contra Costa 

 County, Cal., showed the infestation to be general, but light, except 

 where trees were near packing sheds, drying grounds, or adjacent to a 

 badly infested pear orchard. Many trees were found in such locali- 

 ties showing from 5 to 25 per cent of the nuts infested. During the 

 winter of 1909-10 small quantities of walnuts were frequently bought 

 in the local markets and twice from stands in San Francisco from 

 which codling moth larvae were secured and which showed the char- 

 acteristic injury to the kernel. The writer has also had the same 

 experience with walnuts served on hotel and dining-car tables. Mr. 

 E. J. Hoddy, of the Bureau of Entomology, has frequently, during 

 the past winter, brought in walnuts from various parts of the county 

 showing the injury and presence of these larvae. 



VARIETIES ATTACKED. 



All of the soft-shelled French varieties of walnuts are subject to 

 infestation, and in fact any of the soft-shelled sorts having a fibrous 

 tissue connecting the halves of the shell at base. Moths were reared 

 the past season from the Mayette, Concord, Franquette, and Pari- 

 sienne varieties. 



SEASONAL HISTORY OF THE CODLING MOTH ON WALNUTS. 



So far all observations indicate that only the later broods of larvae 

 attack the walnuts. No walnuts could be found showing early injury, 

 that is, before the shell hardened. Assuming that the larval life in 

 walnuts is the same in length as in apples and pears, the earliest date 

 of infestation would be late August or early September. The Bart- 



