10 BULLETIN 616, U. S. DEPARTMENT OP AGRICULTURE. 



color natural to the ripe fruit are rare in that section, a blending or 

 streaking of the natural red and the gray thrips injury being charac- 

 teristic. The grape (PL III, fig. 3) ranks next to the pomegranate in 

 degree of infestation. It is attacked mostly during the period be- 

 tween growths of the orange. Both leaves and fruit suffer, but 

 chiefly the fruit. In 1911, when citrus trees made but slow and scant 

 growth, a case of severe injury to a small vineyard of Malaga grapes 

 was reported to the writer. This vineyard was located among orange 

 trees which had grown very little during the summer, and the thrips 

 had concentrated there, scarring a large percentage of the berries and 

 distorting many leaves. 



Apricots, peaches, plums, and pears are attacked more rarely ; rasp- 

 berry, very rarely. A part of the scabbing found on the pear is 

 probably due to other species of thrips, although new pear leaves 

 occasionally have been found so badly curled by Scirtothrips citri 

 that they looked diseased. 



The California pepper tree and the Chinese umbrella tree are both 

 very attractive to the citrus thrips, which become abundant on them 

 at certain times of the year. Neither of these trees show the effect 

 of thrips injury from a distance, as do orange trees, and though ovi- 

 position takes place in both varieties eggs are not deposited in 

 umbrella-tree leaves in the fall. The insects do not attack the small, 

 berry-like fruit of the pepper tree. 



The remaining food plants listed in Table I are attacked but rarely 

 and some of them (almond, walnut, and tumbleweed) are probably 

 only accidental food plants. More thrips have been found occa- 

 sionally on the common dock than on any other of the noncultivated 

 plants. 



LIFE HISTORY AND HABITS. 



THE EGG. 



DESCRIPTIVE. 



The egg (fig. 3), as seen in position through the translucent body 

 wall of the parent thrips, is a bluish- white, bean-shaped object meas- 

 uring on an average about 0.185 mm. in length by 0.085 mm. in width. 

 It is comparatively very large, so that five eggs in an advanced stage 

 of development occupying the ovaries at the same time cause consid- 

 erable distention of the abdomen. 



When freed from the ovaries, immediately after deposition, the 

 agg is thick at the base, with the upper two-thirds gradually drawn 

 out into a narrower, necklike portion. The color is then clear ultra- 

 marine and the surface is smooth and glistening. The membrane 

 is flexible, so that the egg may assume other shapes within certain 

 limits. As the embryo develops the bright-red eyes become visible 

 through the transparent shell. 



