U.S. D. A., n. K. Bui. (is, I'art I ( Kevisc-d ). D. F. I. I. SeptemfxT 'JO, 1909. 



PAPERS ON DECIDUOUS FRUIT INSECTS AND INSECTICIDES. 



THE PEAR THRIPS. 



{Eathrlpfi pyi-i Daniel. I 



By Dudley Moulton'. 



Engaged in Drcidiiniif^ Fdd'I Tnarrl fnrcsligations. 



INTRODUCTION. 



This paper l)riny;.s together the resuhs of an investigation of the 

 hfe history, habits, natural enemies, aiul methods of control of the 

 pear thrips (Euthrips pyri Daniel), a pest of deciduous fruit trees in the 

 San Francisco Bay region of California. The investigation was under- 

 taken at the request of the Santa Clara County board of supervisors, 

 who furnished the fimds and liberally granted necessary facilities 

 for a thorough and scientific stuily, and was carried out in the Santa 

 Clara Valley, where the thrips seemed to be at its worst. The investi- 

 gation extended through a period of fifteen months, from February, 

 1904, to April, 1905." 



The writer offers this paper rather as an introduction for futiu-e work 

 than as a completed account, and it is intended especially for the fruit 

 grower, that he may unilerstand the nature of the insect and its injury. 

 The alarm felt for th? safety of the deciduous fruit industry, which 

 the pear thrips caused during 1904 and 1905, in the light of our pres- 

 ent knowledge need not again be experienced, and, although no effect- 

 ive means of control are yet offered, a knowledge of the life habits 

 should do much to clear away tlie uncertainty usually following the 

 first appearance of a destructive pest in any locality. 



OCCTJHRENCE AND DISTRIBUTION. 



The pear thrips is known to exist in the San Francisco Bay counties 

 and along the Sierra Nevada foothills, but it is not known how witlely 

 the pest is distributed outside of these localities. It is still a cjuestion 

 whether the insect is a native of California or an introduced form. 

 The pear thrips may have had some indigenous plant, such as the 



a The writer wishes to acknowledge the work of Mr. Earl L. Morris and Mr. C. T. 

 Paine. He is indebted also to Prof. W. R. Dudley, head (f tlie department of sys- 

 tematic botany, and to Dr. G. 11. Pierce, of the Leland Stanford Junior University, 

 for literature and helpful suggestions, and finally to Prof. Vernon L. Kellogg for his 

 ever helpful suggestions and encouragement. 



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