UNITED STATES DEPARTMENT OF AGRICULTURE 



jru^YWi. 



ft BULLETIN No. 616 yj 



Contribution from the Bureau of Entomology 

 L. O. HOWARD, Chief 



Washington, D. C. 



PROFESSIONAL PAPER 



February 14, 1918 



THE CITRUS THRIPS. 



By J. R. Horton, 

 Tropical and Subtropical Fruit Insect Investigations. 1 



CONTENTS. 



Page. 



Introduction.. 1 



History and distribution 2 



Nature and extent of injury 3 



Dissemination 7 



Food plants 8 



Life history and habits 10 



Seasonal history 22 



Natural checks 24 



Natural enemies 25 



Control experiments 29 



Bibliography 41 



INTRODUCTION. 



The citrus thrips [Scirtothrips 2 (Euthrips) citri Moul.] has caused 

 more or less injury to oranges, grapefruit, and lemons in California 

 for the last 20 or 25 years. Owing to its minute size the insect re- 

 mained undiscovered for many years, and its injury to the fruit was 

 attributed to other causes, such as wind whipping, freezing, etc. 

 About the year 1908 the injury became so severe in Tulare County 

 that the old theories began to be doubted and the need of expert in- 

 vestigation was realized. The preliminary examination in behalf of 

 the Bureau of Entomology was made by Dudley Moulton (2) 3 and 

 resulted in a description of the insect and its injury. Subsequently 

 the bureau undertook a thorough investigation of the life history and 

 control of the insect, this project being started at Lindsay, Tulare 

 County, Cal., in 1909. A report of progress by Jones and Horton 

 (5) and a Farmers' Bulletin on the control of the thrips by the 

 writer (15) have appeared since. 



1 Transferred to Cereal and Forage Insect Investigations, October 1, 1917. 



2 Hood (14) places this insect in the genus Scirtothrips on the apparently adequate 

 grounds that the thorax is finely, transversely striate and the abdomen clothed with 

 minute hairlike processes. 



8 See Bibliography, p. 41. 



13138°— 18— Bull. 616 1 



