AN INTERNAL PARASITE OF THYSANOPTERA. 



47 



To summarize all of the rearing experiments conducted during the 

 summer of 1911, the Ufe cycle of this insect required from 28 to 44 

 days, but the average was between 30 and 34 days. (See fig. 10.) 



FIRST APPEARANCE IN THE SPRING. 



In 1911 tliis insect was not observed until June 15, although a very 

 careful lookout had been kept from early in the spring. Undoubtedly 

 future work will show that- this insect becomes active considerably 

 before this time and probably as early as the mi(hlle of March at 

 least. 



LAST APPEARANCE IN THE FALL. 



In 1910 parasitized thrips were found as late as November 10 and 

 after that, although thrips larvae were collected, no signs of para- 

 sitism could be found. In 1911 

 very few adults emerged from '^^^ 

 the pupse after October 1, 

 although adults were observed 

 in the field as late as October 

 21. On November 10, 1911, 

 a large collection of thrips 

 larvae gave only 9 parasitized 

 specimens, while a later col- 

 lection, made December 8, 

 gave one parasitized form, 

 which would indicate that 

 this parasite had about ceased 

 its work. 



s 6 7 8 



9 /O // /^ /3 /4 /S /S /7 



Fig. 8. — Diagram illustrating length of time from ovi- 

 position to first evidence of parasitism for 353 indi- 

 viduals of Tliripoctenus russelli. (Original.) 



NUMRER OF GENERATIONS. 



The experiments made during 1911 have shown that the female of 

 this insect may begin oviposition in a very few hours after emerging 

 from the pupa. Because of tliis we can expect a new generation to 

 be begun the same day that the female emerges, provided she finds 

 host larva?. Therefore, if we take March 15 as a point when this 

 insect becomes active in the spring and November 10 as the date 

 that this insect ceases to ovi])osit, we might obtain as many as 8 

 generations, provided each required only 28 (hi3^s for development, 

 or onl}^ 5 generations if the nuiximum period for deA^eloj)ment was 

 required. 



HIBERNATION. 



Tliripoctenus russelli passes the winter in the pupal stage, the 

 different individuals evidently hibernating as soon as the tempera- 

 ture drops sufficiently low to check development. Pupse taken to 

 Washington, D. C, all entered hibernation as early as October 1, 

 while the adults were still emerging at the laboratory in Com])ton, 



