THE ORANGI-: TUHll'S. 6 



Blood. St. Alichaol. Ilomosassa, and seedlings) ; Citrus nohilis (Sat- 

 sinna and tangerines) ; Citnts decumana (grapefruit) ; Citrus medica 

 var. Ji//ion (lemon) ; Citrus medica var. acida (lime, varieties of) ; 

 and Citrus japouica (knmquat). 



The follo^ving miscellaneous plants are infested : Punica gramatum 

 (pomegranate) ; T'/f/.s- rinifera (European grape, varieties of) ; 

 ScJiinus moUe (California pepper tree); "umbrella tree;" Pyrus 

 communis (pear); Prunus anneniaca (apricot); Prunus pcrsica 

 (peach) ; Prunus domestica (European plum, varieties of) ; Salix sp. 

 (■willow) ; Rnmex sp. (dock) ; Portulaca oleracea (purslane) ; Olea 

 euro pea (olive) ; Rub us ida'us (red raspberry) ; Rosa sp. (rose) ; 

 SoJanuiu sp. 



CHARACTER AND EXTENT OF INJURY. 



Injury to citrus trees and fruit is caused directly by the feeding 

 of both adults and larvir upon the surface of the parts attacked. 

 This feeding may be on the young fruit (Plate I, figs. 1, 2) , the nearly 

 mature fruit (Plate II), or the new, tender foliage (Plate III), and 

 generalh' takes place on all of these. The injury to foliage is gen- 

 erally on young leaves, but may also occur on the axillary buds. 



The manner of feeding of both the adult and larva of the thrips is 

 identical, and consists in piercing the plant tissues with the sharp 

 mouthparts with which both stages are equipped and then rasping 

 the wound by a " rooting " motion of the head. The vegetable juices 

 thus liberated from the plant cells are sucked into the alimentary 

 canal of the insect. The characteristic marking or scabbing of the 

 fruit, so noticeable at picking time, is started when the fruit is very 

 small — just after the petals have fallen from the blossoms. This 

 scabbed area is small at first, but as the fruit grows and the thrips 

 continue to feed the markings deepen and at the same time the area 

 of injur}' is enlarged. The continued feeding of a large number of 

 thrips results in the scabbing of nearly the entire surface of the fruit. 

 Often the marking is so large and deep over a portion of the orange 

 that it causes the fruit to be misshapen and aborted. Frequently the 

 entire surface is scarred while the fruit is still small. ^\ ith the result 

 that it ceases to grow and falls from the tree. 



Orange trees in the Tulare County citrus belt make about four dis- 

 tinct growths a year, and it is on this tender foliage that the orange 

 thrips multiply in greatest numbers. The feeding of large numbers 

 of these little insects causes the young leaves to curl and become dis- 

 torted and the whole growth to present a sickly appearance. Young 

 trees are often held back a year or more in growth by the prompt 

 destruction of the terminal buds soon after these make their 

 appearance. 



