50 INJURIOUS AND BENEFICIAL INSECTS OF CALIFORNIA 



THYSANOPTERA (Order) 



FRINGED WINGED INSECTS 



THRIPS 



The numerous species of the minute fringed-winged insects, known 

 as tli rips, are placed in a single order as given above. These insects, 

 though exceedingly small, may be readily observed by simply shak- 

 ing almost any flower, especially the sunflowers and their allies, into 

 the hand and observing the small yellowish or brownish slender 

 individuals crawling out in the palm of the hand. They hop and 

 fly very readily. The eggs are laid upon the outside, or within the 

 tissues of the plant. In the latter case the female inserts the egg 

 with her sharp ovipositor. The insects have direct, simple or incomplete 

 transformations, the larva? greatly resembling the adults. The larvae 

 of some species go into the ground for hibernation and pupation, 

 the adult insects emerging in the early spring. The mouth-parts 

 are modified so that the insects pierce or chafe rather than bite, and 

 due to their constant work and tremendous numbers are able to 

 accomplish very disastrous results. Some species work principally 

 upon the young buds and flowers, though they often do considerable 

 damage to fruits and foliage. 



In this State thrips have been considered most serious pests, espe- 

 cially in the Sacramento and San Joaquin valleys, where thousands 

 of dollars have been spent in their control. 



During the last two years, however, the amount of spraying has 

 been greatly reduced because many growers believed that the cost 

 did not warrant the benefits derived. 



The control measures vary somewhat and are given under each 

 individual species. 



Several species have been known to be attacked by internal 

 liymenopterous parasites, but the exact amount of this parasitism 

 for the various species is not well known. 



THE WHEAT THRIPS 29 



Frankliniella tritici (Fitch) (Family Thripidae) 



[Euthrips tritici (Fitch)] 



(Thrips tritici Fitch) 



(Fig. 44) 



Description. — The adults of this species are noticeably longer than 

 any of the other common species. The color is amber or brownish and 

 the head and thorax are distinctly yellow or orange-colored, which make 

 it easily recognized at once with the naked eye. The eggs are very 

 minute, globular and red. The young greatly resemble the adults, but 

 are much smaller and a little paler. 



Life History. — The life history of this species is practically the 

 same as for the bean thrips. 



Nature of Work.— Besides causing the small discolored spots on 

 the foliage, this species is very destructive to the pistils of the flowers 



2l) This species is also known as the flew-' grain and strawberry thrips and is the 

 common alfalfa thrips of California. 



