CHAPTER XVIII 

 ORDER THYSANOPTERA* 



The Thrips 



The members of this order are minute insects with wings or wingless. 

 The winged species have four wings; these are similar in form, long, 

 narrow, membranous, not plaited, with but few or with no veins, and 

 only rarely with cross-veins; they are fringed with long hairs, and in 

 some species are armed with spines along the veins or along the lines 

 from which veins have disappeared. The mouth-parts are formed for 

 piercing and sucking. The tarsi are usually two-jointed and are bladder- 

 like at the tip. The metamorphosis is gradual, but deviates from the 

 usual type. 



These insects are of minute size, rarely exceeding 2 mm. or 3 mm. 

 in length. They can be obtained easily, however, from various flowers, 

 especially those of the daisy and clover. Ordinarily it is only necessary 

 to pull apart one of these flowers to find several thrips. They are in 

 many cases very active insects, leaping or taking flight with great 

 agility. In case they do not leap or take flight when alarmed, they 

 are apt to run about and at the same time turn up the end of the 

 abdomen in a threatening manner, as if to sting. In this respect they 

 resemble the rove-beetles. 



The body is long (Fig. 390). The head is narrower than the thorax, 

 without any distinct neck. The antenuce are filiform or moniliform 

 and consist of from six to nine segments ; they 

 are alwaj'S much longer than the head and may 

 be two or three times as long. The compound 

 eyes are large, with conspicuous facets, which 

 are circular, oval, or reniform in outline. Three 

 ocelli are usually present in the winged forms, 

 but sometimes there are only two ocelli ; wing- 

 less species lack ocelli. The mouth parts are 

 fitted for piercing and sucking ; they are in the 

 form of a cone which encloses the piercing or- 

 gans. The cone is composed of the clypeus, . . , . 



labnmi, maxillary sclerites, and labium. The ^^' ^^^' "^^' 



piercing organs consist of the left mandible (the right mandible is 

 vestigial) and the two maxillae. Each maxilla is composed of two 

 parts: first, the palpus-bearing maxillary sclerite; and second, the 

 maxillary seta. For detailed accounts of the mouth-parts see Hinds 

 ('02) and Peterson ('15). The above statement regarding the mouth- 

 parts is based on the paper by Peterson. The mouth-parts of the 

 Thysanoptera bear a striking resemblance to those of the Hemiptera 



*Thysan6ptera: ihysanos (dvaavos), fringe; pteron {irr^f^bv), a wing. 



(341) 



