4 BULLETIN 616, U. S. DEPARTMENT OF AGRICULTURE. 



" stem-end ring " is the most characteristic form of fruit injury, 

 and is caused by the thrips feeding and ovipositing in a circle under 

 the protection of the sepals when the fruit is small, the injury ex- 

 panding as the fruit grows. Injury resulting from feeding punctures 

 in mature fruits appears as brownish, glossy discolorations due to 

 cell sap drying on the surface. A large proportion of the badly 

 marked fruit is undersized owing to failure to mature normally, 

 and much of it is at times distorted by failure of the injured tissues 

 to grow. 



The more characteristic injury to the leaves is the grayish streaks 

 and areas (PI. II, fig. 2) and curling. At times cuplike depressions 

 or pockets resembling aphid galls are formed, but oftener the leaves 

 are crinkled or even tightly curled (PL II, figs. 1 and 3). 



The unfolding leaf buds and especially the terminal buds are 

 often attacked with such severity as to cause them to wither and 



die, these turning brown or black and 

 finally dropping off. 



DAMAGE TO FRUIT. 



DROPPING. 



In exceptionally severe infestations, 

 much of the young fruit is punctured 

 over its entire surface during the first 

 three weeks following the blossoming 

 pig. 3. — a. Eggs of the citrus period and thus is prevented from ac- 



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egg of the citrus thrips. eventually dropping to the ground. An 

 ig y magm e . rig na .) appreciable percentage of the crop is 

 lost in this way in certain orchards of Tulare County, Cal., in cer- 

 tain years. 



SPLITTING. 



While only a small proportion of the usual fruit splitting is caused 

 primarily by thrips, a certain amount of splitting of young oranges 

 does occur every season as a result of the long-continued feeding of 

 thrips over an area usually near the navel end of the fruit. The 

 affected tissues die and dry out and the scabbed area, unable to ex- 

 pand with the growing fruit, cracks (PL I). 



MALFORMATION. 



From less than 1 to as much as 6 per cent of the orange crop, 

 depending upon the orchard and the season, is so badly deformed by 

 the citrus thrips that it must be culled out and sold at the packing 

 house for whatever it will bring. The better culls usually command 



