8 BULLETIN 173, U. S. DBPAETMBNT OF A.GBICTTLTUBE. 



Table I. — Yield of prunes for the Santa Clara Valley, 1900-191.;, inclusive. 



Season Yield of dried 

 beason. fnljt 



Season Yield of dlied 



beason. frui( 



1900 



1901 1 



Pounds. 

 120,000,000 



35, 000, 000 

 120,000,000 



90,000,000 

 100,000,000 



50,000,000 

 120,000,000 



Pounds. 



1907 50,000,000 



1908 40,000,000 



1909 85,000,000 



1aln 1/ 35,000,000 



lyw V 40,000,000 



1911 100,000,000 



1912 65,000,000 



1902 



1903 



1904 



1905 



1906 





1 Severe frost. 



In 1911 the pear thrips probably caused a heavy loss in spite of 

 the fact that there were not more than one-half as many thrips 

 present in this valley as in 1910. The good prune crop in the Santa 

 Clara Valley in 1911 was due to light thrips injury and the very 

 heavy rainfall. The amount of rainfall, which was about 8 inches 

 more than the normal, not only placed the trees in excellent shape 

 to bear a heavy crop, but, coupled with other climatic conditions 

 during the early part of 1911 and latter part of 1910, lessened the 

 work of the thrips very materially. Notwithstanding a favorable 

 fruit year from a weather point of view, thrips in some places caused 

 a great amount of damage. The thrips damage in the Santa Clara 

 Valley for 1910 was caused principally by the adults, with very 

 little larval work, while for 1911 it was just the reverse, the adults 

 doing comparatively little injury because of less numbers and strong 

 fruit buds as a result of the heavy winter rains. The scarcity of 

 adult thrips in 1911 may have been due to several causes. Two 

 heavy rains during the early part of April of the previous year 

 knocked off many young larva? before they were sufficiently mature 

 for transformation. In addition the season for pupating, June to 

 December, 1910, was abnormally dry, showing a deficiency in rain- 

 fall of 5.28 inches, while the emergence period in the spring of 1911 

 was unusually wet and cold. All of these conditions caused a higher 

 mortality than would be the case under normal conditions. However, 

 in orchards which showed comparatively few adults the larvae were 

 sufficiently abundant to riddle the foliage and cause much of the 

 young fruit to drop. The heavy rains during the emergence period 

 also checked to some extent the work of the adults. 



In estimating the economic loss to the fruit industry of California 

 caused by the pear thrips it is necessary to begin with the year 1904, 

 when it was first known that the insect was doing commercial damage, 

 and continue down to the present time. An attempt will be made 

 to give a fair estimate of the amount of damage done yearly to the 

 prune industry alone in the Santa Clara Valley for the years 1904 

 to 1911, inclusive. 



