THE CITRUS THKIPS. 



9 



range of food plants is wide and includes practically all the citrus 

 fruits grown in California, certain deciduous fruits and nuts, a few 

 ornamentals, and several noncultivated plants. 



Table I. — Food plants of the citrus thrips in order of importance. 



Group I, generally infested. 



Group II, occasionally infested. 



Group III, rarely infested. 



1. Sweet oranges. 



6. Pomegranate (Punka granatum). 



11. Peach. 



2. Mandarin orange ( Citrus 



7. Grape. 



12. Plum. 



nobilis). 



8. California pepper tree (Schinus 



13. Pear. 



3. Pomelo, or grapefruit. 



molle). 



14. Raspberry. 



4. Lime andlemon. 



9. Chinese umbrella tree (Melia 



15. Pecan. 



5. Kumquat( Citrus japonica). 



azedarach umbraculifera). 



16. Walnut. 





10. Apricot. 



17. Olive. 



18. Rhubarb. 



19. Dock (Rumex sp.). 



20. Purslane (Portulacaolcracca). 

 31. Willow. 



22. Wild morning-glory (Convol- 



vulus sp.). 



23. Nightshades (Solanum spp.). 



24. Almond. 



25. Tumble weed (A mara nthussp.). 



The sweet oranges suffer greatest damage from the citrus thrips, 

 especially the varieties known as Washington, Thompson's Improved, 

 and Australian navels, and the Parson Brown and Homosassa. 

 Valencias are damaged considerably when the trees are young, and 

 the fruit is attacked at all times, but not severely. Blood oranges 

 generally escape with very little injury. The Washington navel 

 orange covers a greater acreage in Tulare County than all other 

 varieties together. This fact probably accounts for this variety 

 holding first rank as a food plant of the thrips. As a rule not more 

 than 25 per cent of the Valencia crop is injured sufficiently to depre- 

 ciate its market value ; and it is rarely that more than 10 per cent of 

 blood oranges show any marking whatsoever. Oranges of the Man- 

 darin group, especially the tangerines, are subject to very severe mark- 

 ing, for the reason that they remain attractive to thrips until nearly 

 mature. The Satsuma often becomes much distorted because of 

 thrips marking, but this fruit is an unimportant crop in California. 

 Pomelos, limes, and lemons (PL III, fig. 1) share nearly equally ir 

 severity of thrips marking, but the trees are not often severely in- 

 jured, as the foliage is not particularly attractive to the insect. 

 Limes often become severely scarred, the rind remaining tender 

 throughout the growth of the fruit. Of all the citrus fruits the 

 kumquat is the least attractive to thrips, rarely more than from 2 to 

 5 per cent of the fruit becoming slightly scarred by them. 



The pomegranate (PL III, fig. 2) is the most preferred fruit other 

 than citrus. Pomegranate trees mostly are planted as ornamentals 

 bordering citrus groves, but in 1910 in a 20-acre pomegranate 

 orchard at Lindsay, CaL, 75 per cent of the fruit showed the charac- 

 teristic scabbing of the citrus thrips. Pomegranates of clear, red 



