THE CITRUS THRIPS. 3 



Although the insect occurs in injurious numbers in Arizona, thus far 

 it has been taken only in the Salt River Valley near Phoenix and 

 Mesa (fig. 2). Dr. A. W. Morrill informed the writer by letter that 

 he thought he detected traces of thrips injury in an orange grove near 

 Yuma,_but specimens have not been taken there. 



POSSIBILITY OF ITS OCCURRENCE ELSEWHERE. 



No verified reports of the occurrence of the citrus thrips in States 

 or countries other than the foregoing have been made, although it 

 is said to occur at Hermosillo, Sonora, Mexico. There are various 

 reports of thrips injuring citrus 

 fruits, the species concerned being 

 often in doubt. Thus, Tower x 

 states that certain scars found on 

 oranges in Porto Rico probably 

 are caused by thrips which were 

 present in the trees in great num- 

 bers, but the identity of the thrips 

 is not given. Eolfs, Fawcett, and 

 Floyd 2 describe injury to oranges 

 in Florida by a thrips which ap- 

 pears to be Frankliniella (Euthrips ) 

 tritici Fitch, if indeed the injury 

 illustrated by them is caused by 

 thrips. The citrus thrips does not 

 occur in southern Louisiana, and 

 doubtless could not thrive there 

 because of the high humidity and 

 heavy rainfall, and for the same reason probably does not occur in 

 Florida. 



NATURE AND EXTENT OF INJURY. 



Fig. 2. — Map showing present-known dis- 

 tribution of the citrus thrips in Ari- 

 zona. (Original.) 



The citrus thrips obtains its food by puncturing the tissues and 

 draining the contents of the cells, causing the cell walls to collapse. 

 Growth expansion of the surrounding living cells leaves the punc- 

 tured and dead areas sunken and distorted. The very characteristic 

 scabbing of the fruit is caused by the dead and dry cell walls being 

 forced outward by the growing cells beneath, the resultant scabs 

 often covering a large portion of the rind. The various rings, 

 streaks, splashes, and other patterns in the tissues result from the 

 almost incessant movement of the thrips as they feed (PL I). The 



1 Tower, W. V. Insects injurious to citrus fruits and methods for combating them. 

 Porto Rico Agr. Exp. Sta. Bui. No. 10, p. 20. 1911. 



2 Rolfs, P. H., Fawcett, H. S., and Floyd, B. F. Diseases of citrus fruits. Fla. Agr. 

 Exp. Sta. Bui. 108, p. 32-33. 1911. 



