THE PEAR THRIPS IN CALIFORNIA. 7 



namely, "pear thrips," has been more extensively used, following 

 the original designation of the insect, because the species was first 

 described from specimens taken upon pear trees. The word "thrips" 

 is a general term for the species of the order Thysanoptera and is 

 sometimes erroneously applied to certain other insects, as the grape 

 leafhopper (TypJdocyba comes Say). The word "thrips" is both 

 singular and plural. 



ECONOMIC IMPORTANCE. 



DESTRUCTIVENESS. 



This minute insect, which until 1904 was unknown to science, is at 

 present one of the most important insect pests with which the growers 

 of deciduous fruits in the San Francisco Bay region and adjoining 

 counties have to contend. The rapidity with which the insect 

 spreads, its suddenness of attack and complete blasting in a few days 

 of all prospects for a crop of fruit, and the difficulty experienced in its 

 control, combine to make its subjugation a matter of considerable 

 difficulty. Moreover, as the insect is each year developing an ability 

 to subsist on other and new food plants, its capabilities for dissemi- 

 nation become correspondingly increased. There is no reason to 

 believe that the thrips will disappear in a few years, and it should be at 

 once realized that only the most careful attention each year to neces- 

 sary control measures will make it possible to continue the profitable 

 culture of fruit in regions where this insect is present in any con- 

 siderable numbers. 



In the Santa Clara Valley this insect has been worse some years 

 than others, notably in 1905, 1907, 1908, 1909, and 1910, but it is 

 safe to say that from now on the maximum prune crop possible for 

 this valley will never again be reached unless every orchardist does 

 the utmost in his power to control the thrips. While it may be pos- 

 sible for unfavorable weather conditions to reduce the possibility of 

 a good crop of 100,000,000 pounds of dried prunes for this valley to 

 something like 40,000,000 or 50,000,000 pounds, the thrips, in a 

 great measure, has been responsible for the small crops since 1907, 

 and will continue to be so, first, by killing the fruit buds before they 

 bloom; secondly, by depositing the eggs in the fruit stems, and, 

 thirdly, by the feeding of the larvae on the fruit, causing it either to 

 drop prematurely or to develop misshapen and scarred on the trees. 

 While the thrips is doing much serious work in the Santa Clara 

 Valley to cherries and pears and the damage done to different varie- 

 ties of peaches is increasing, yet on account of the small acreage of 

 these fruits the chief loss from a commercial standpoint is to the 

 prune industry. Some idea of the destruction caused by the pear 

 thrips during the previously mentioned bad years may be gained 

 from the following figures, giving the approximate yield of prunes in 

 pounds each year for the years 1900 to 1912, inclusive. 



