U. S. D. A.. B. E. Tech. Ser. 12, Pt. VII. Issued February 11, 1909. 



MISCELLANEOUS PAPERS. 



THE ORANGE THRIPS. 



By Dudley Moulton. 

 Engaged in Deciduous Fruit hisect Innsfigations. 



INTRODUCTORY. 



The orange thrips, Euthrips citn, a new species, described in this 

 article, has become a very important orange-tree pest in the southern 

 San Joaquin Valley of California and has been the subject of special 

 investigation. The writer has been able to talk with many orange 

 growers and packers, and with men who have developed extensive 

 nurseries, and the following notes have been gathered largely from 

 these sources. 



DISTRIBUTION. 



The San Joaquin orange belt extends along the western border of 

 the Sierra foothills from a point about east from the city of Fresno, 

 southward to a short distance below Porterville, with, some orchards 

 as far south as Bakersfield. The belt is not at all continuous, but is 

 broken in many places because of improper soil conditions, frosts, 

 and the lack of water for irrigation. The thrips is distributed every- 

 where throughout this belt, but is not found, so far as I have been 

 able to learn, in any other orange section of California. 



EXTENT AND NATURE OF INJURY. 



The orange groves in the San Joaquin belt are wonderfully profit- 

 able, for as much as $2,000 per acre has been realized in a single 

 year from full-bearing orchards. This thrips problem is, therefore, 

 a very important one when we consider the large area which is 

 planted and is being planted. 



Curled and thickened leaves and marked oranges, the characteristic 

 signs of the thrips, have been known for from ten to fifteen years, but 

 only recently have these injuries been attributed to the thrips. The 

 thrips has been increasing rapidly in numbers, until now the annual 

 loss to the orange growers amounts to many thousands of dollars. 



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