32 



MISCELLANEOUS PAPERS. 



host for ])upation. This, of course, will vary with the different 

 species of thrips attacked. Two years constant work with Helio- 

 tJirips fasciatus has shown that, at least in southern California, the 

 majority of the larvae of this species ])upate in rubbish, in cracks, or 

 under clods of earth. Therefore, when Heliotlirips fasciatus is the 

 host of this parasite the latter will be found to form its pupae in the 

 same places. TJirips tohaci and Evthrips trltici botli enter the 

 ground and form oval cells in which to pupate, and thus, when 



eitlier of these thrips is the host, the 

 pup^e of this parasite will necessarily 

 be formed underground. 



The parasitic larva, when ready 

 to pupate, splits the skin of the 

 host larva at the anterior end and 

 then gradually works the skin off 

 at the anal end. This molted skin 

 in many cases niay be seen lying 

 behind the parasitic pupa. 



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DESCRIPTION. 



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When newly formed, the pupa 

 of Thripoctenus russelli is almost 

 white, but the intestinal tract in 

 the thorax and anterior part of the 

 abdomen is a bright crimson, sim- 

 ilar to the spot in the prepupa of 

 the host that, as stated previously, 

 first indicates parasitism. After a 

 short exposure to the air the edges 

 of the body and appendage cases 

 of the parasitic pupa begin to 

 darken. At first this darker color 

 is of a bluish tint, but it changes 

 more and more to black until the 

 pupa is shining black excepting that portion where the reddish color 

 still shows through. The pupa (fig. 5), which is flattened oval, is 

 rounded in front, but with a slight notch at the center, and is followed 

 by a distinct neck the sides of which are convex. Posterior to this 

 it is abruptly widened to its fullest extent and forms prominent 

 shoulders. The sides then converge very slightly to the beginning 

 of the abdominal segments. The abdomen forms a well-rounded 

 oval, the appendages all being closely appressed to the underside of 

 the pupal shell. 



Fig. 4. — Diagram illustrating length of time 

 from appearance of jiarasitism to formation 

 of parasite pupae of Thripoctenus russelli, 

 July-October, 1911. (Original.) 



