THE MONTHLY BULLETIN. 



29 



THYSANOPTERA (Order). 



THRIPS. 



The numerous species of the minute f ringed-winged jnsects, known 

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

 though exceedingly small, may be readily observed by simply shaking 

 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 or incomplete transformations, the larva greatly 

 resembling the adults. The pupa of some species have a quiescent stage, 

 thus differing from most insects having incomplete metamorphosis, in 

 which this stage is very active, differing from the adults only by the 

 small wing pads. Those species having a quiescent pupal stage are 

 characterized by the larvae going into the ground for pupation and 

 remaining there during the winter, the adult insects emerging in the 

 early spring. The mouth-parts are modified so that the insects chafe 

 rather than bite, and due to their constant work and tremendous num- 

 bers are able to accomplish very disastrous results. They work prin- 

 cipally upon the young buds and flowers, though they often do consid- 

 erable damage to fruits and foliage. 



In this State thrips are among the mo.st serious pests, especially in 

 the Sacramento and San Joaquin valleys, where thousands of dollars 

 are spent each year in protecting the orchards. 



The control measures vary somewhat and are given under each indi- 

 vidual species. Several species have been known to be attacked by 

 internal hymenopterous parasites, but the exact amount of this para- 

 sitism for the various species is not well known. 



THE BEAN THRIPS. 



Heliothrips fasciattis Pergande. 

 (Fig. 27.) 



General Appearance. — The adult insect is black with head and 

 thorax dark brown ; antennaB are whitish with tips dark ; legs are black 

 and yellow ; front wings are blackish with white base ; posterior wings 

 uniformly yellow with dark fringes. The young stages are lighter in 

 appearance than the adult. 



Life History. — According to Mr. H. M. Russell the insects hiber- 

 nate in the adult stage only, under leaves, rubbish, etc. They begin 

 to emerge about January and immediately begin egg-laying. The eggs 

 are inserted in the leaves or tender stems. The young begin feeding 

 soon after hatching. When ready to pupate the larvae seek shelter 

 under rubbish or in the ground, where the nymphal stage is completed 

 and the adults emerge. There is an overlapping of broods so that 



