30 



MISCELLANEOUS PAPERS. 



this ])arasitc emerged they were })laced in these vials with fresh 

 leaves heavily infested with healthy larvae of this species of thrips. 

 In tliis way ovi])osition could be carefully watched, and when desired 

 the parasites were removed to fresh vials. The larva? in which the 

 parasites had oviposited were carefully changed to fresh leaves 

 whenever necessary until they became mature and pupated. 



STAGE OF THRIPS SHOWING PARASITISM. 



Although hundreds of j)arasitized thrips have been observed in 

 the laboratory, in no case has the parasitism ever been evident in 

 any stage but that of the prepupa. The larva? have been carefully 

 examined at regular intervals but until they have changed to pre- 

 pujise it is impossible to ascertain which of the larvie are actually 

 parasitized. In the prepujral stage parasitism develops raj)idly, 

 the growth of the host is retarded, and its death follows shortly. In 

 every instance in which a prepupa has changed to a pupa an adult 

 thri])s has emerged from this stage, so that, in so far as our present 



knowledge is complete, the 

 prepupal stage of the thri])s 

 is the only one in which 

 parasitism is evident. 



APPEARANCE OF PARA- 

 SITIZED PREPUPiE. 



Parasitism first becomes 

 evident two or three days 

 after the thrips larvae have 

 changed to the prepupal 

 stage, and, in case unpara- 

 sitized prepupiB are in the 

 vial, often after these have 

 further changed to the pupal stage. Parasitism is first indicated in 

 the semitransparent host prepupa when the color contents of the 

 antennae, head, and anal end of the thrips are removed through the 

 feeding of the internal parasite, leaving the parts hyaline. At the 

 same time there is seen an internal deepening of color in the center 

 of the body. As the feeding of the parasitic larva progresses, the 

 color is more and more directed to the center of the body, and the 

 edges of the body begin to appear hyaline. At about this time the 

 legs of the host larva collapse and sprawl in all directions. A few 

 hours after parasitism is first noticed, the body of the thrips prepupa 

 is swoUen and rounded, the original shape being lost. The body is 

 entirely hyaline or colorless except an inner cylinder of deep crimson 

 in Heliotlirips fasciatus (fig. 3), or yellow in Thrips tabaci Lindeman 

 and Euthrips tritici Fitch. 



Fig. 2.— Cage for rearing parasites. (From Banl<s.) 



