THE CITRUS THEIPS. 
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 grunatum). 
11. Peach. 
2. Mandarin orange ( Citrus 
7. Grape. 
8. California pepper tree (ScMnus 
12. Plum. 
nobilis). 
13. Pear. 
3. Pomelo, or grapefruit. 
molle). 
14. Raspberry. 
4. Lime and lemon. 
9. Chinese umbrella tree (Melia 
15. Pecan. 
5. Kumquat ( Citrus japonica). 
azedarach umbraculifcra). 
16. Walnut. 
10. Apricot. 
17. Olive. 
18. Rhubarb. 
19. Dock (Rumex sp.). 
20. Purslane (Portulaca olcracca). 
31. Willow. 
22. Wild morning-glory (Convol- 
vulus sp.). 
23. Nightshades (Solanum sppr). 
24. Almond. 
25. Tumbleweed(ylmara7i^wssp.). 
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. 
Yalencias 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 (PI. Ill, fig. 1) share nearly equally in 
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 
