236 PROCEEDINGS ENTOMOLOGICAL SOCIETY 



Museum, under the name Thripoctenus russelli. The following 

 is a brief summary of the life history and habits of this insect 

 as observed by the writer and his assistant, Mr. J. E. Graf. 

 It may also be added that every important fact discovered 

 concerning this insect has been independently observed and 

 checked up by either the writer or Mr. Graf. 



This parasitism first becomes evident two or three days after 

 the thrips larvae have changed to the prepupal stage and often 

 after the normal insects have further changed to the pupal 

 stage. The first indication is an extracting of color from the 

 antennae, head, and anal end of the thrips, leaving these hya- 

 line, and an evidence of a deepening color in the center of the 

 body. The attacked insect still has the power of motion, but 

 as the feeding continues the color is more and more drawn to 

 the center of the host and the edges of the body begin to ap- 

 pear hyaline, then the limbs collapse and sprawl in all direc- 

 tions, and the thrips loses all power of motion. Within a few 

 hours after the parasitism is first noticed the insect has be- 

 come shortened and more rounded and entirely hyaline or col- 

 orless, with the exception of an inner cylinder of deep crimson 

 color in Heliothripsfasciatus or yellow in Thrips tabaci Lind. or 

 Euthrip* tritici Fitch. The parasitic larvae emerge and 

 pupate within from 2 to 11 days after the parasitism becomes 

 evident, but, in over 66 per cent of the cases observed, in from 

 3 to 4 days. When the parasite is ready to pupate, the skin 

 of the host is split and gradually worked off at the anal ex- 

 tremity and the parasite pupates in front of this cast skin, in 

 whatever location the host had sought to change to a pupa. 1 

 The pupa is more or less of a flattened oval, 0.78 to 0.85 mm. 

 in length and 0.30 to 0.32 mm. in width at the shoulders. 

 The head is rounded in front and is followed by a distinct 

 neck behind which the body is abruptly widened to its fullest 

 extent. Posterior to this the sides, at first more or less par- 

 allel, converge very evenly to the posterior extremity. The 

 newly formed pupa is almost white, except for the crimson 

 cylinder in the center of the body, but in a short time it be- 

 comes gradually darker until it changes to shining black. 

 During the summer the pupal stage varied in length from 16 

 to 28 days, but over 66 per cent of the specimens reared com- 

 pleted this stage in from 17 to 20 days. 



The adult in emerging breaks off the covering of the face 

 and splits the pupa case down the back, after which it frees 

 its fore legs and by means of these slowly pushes the case 



1 H. fasciatus in some cases pupates in a curled-up leaf, but more 

 often has been observed in rubbish or in cracks or under lumps of 

 earth . 



