32 



BULLETIN 173, U. S. DEPARTMENT OF AGEICULTUEE. 



of emergence by some two or three days. This was particularly 

 noticeable in pear orchards used in cultivation experiments in Contra 

 Costa and Solano Counties. In the plowed portions which were free 

 from weeds, the surface dried out and warmed up more rapidly and 

 thrips came out in numbers and into the trees three days earlier than 

 on the unplowed part of the orchard, which was covered witrTa rank 

 growth of vegetation. The shading of the soil by the vegetation 

 seems to result in holding the thrips within the ground several days 

 later, or else they spend some time on this succulent growth before 

 going into the trees. 



The following tables give the emergence records for the years 1909 

 1910, 1911, and 1912 for Santa Clara County (San Jose, Table IV)- 



200 

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 /70 



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 /20 



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 20 

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/rfBRUAXy MARCH 



Fig. 14.— Curve showing emergence of pear thrips at San Jose, Cal., 1911. (Original.) 



for 1909 and 1910 in Contra Costa County (Walnut Creek, Tables V 

 and VI), and for 1910 in Solano County (Suisun, Table VII). These 

 tables show the total number of thrips emerging on the given dates 

 from soil in the cages. For the San Jose records, all the cages con- 

 taining soil samples from infested prune orchards were placed in the 

 ground at the laboratory. For the records in Contra Costa and 

 Solano Counties, part of the cages were brought to the laboratory 

 and buried in the ground and part were left in the ground under the 

 trees in infested orchards. (See fig. 6 for type of cage used for the 

 field emergence records in the northern counties.) It was not pos- 

 sible to take the emergence every day, but, so far as possible, counts 

 were made at regular intervals. 



