OP WASHINGTON, VOLUME XIII, 1911. 235 



A TRUE INTERNAL PARASITE OF THYSANOPTERA. 



BY H. M. RUSSELL. 



In view of the recent interest manifested in the order 

 Thysanoptera and the tremendous importance several species 

 of this group have assumed economically, it is of interest to 

 record, at this time, the rearing of a parasite from a number 

 of different species of thrips. At Compton, California, on 

 December 10, 1910, four specimens of the prepupal stage of 

 Heliothrips fasciatus Perg. gave unmistakable signs of para- 

 sitism. These were among a lot that had been collected in 

 the larval stage on November 10, 1910, in order to ascertain 

 how this thrips passes the winter, and this lot comprised the 

 last that the writer was able to find that fall. By December 

 13, two of these prepupae had been killed, while from the 

 others parasitic larvae had emerged and changed to naked 

 pupae. These were sent to the Bureau of Entomology of the 

 U. S. Department of Agriculture, in the hope that the adult 

 could be reared and determined, but unfortunately both died 

 and this was impossible. As soon as the weather permitted, 

 the author again took up the work of collecting the larval 

 form of this thrips, in order to rear the parasite. Although 

 this work was begun in February, 1911, it was not until June 

 15 that any parasitized specimens were found. Then a col- 

 lection of four larval forms was made at Compton, California, 

 one of which was parasitized. On July 3,- 1911, one prepupa 

 showed plainly that it was parasitized, but died without chang- 

 ing to pupa. 



While collecting thrips material at Hollywood, California, 

 on June 29, the author observed a very minute hymenopteron 

 on the under side of a bean leaf in company with larva.' of 

 ffcliothrips fasciatus and, impressed with the idea that this 

 was the parasite of the thrips, it was carefully watched through 

 a small hand lens and appeared to oviposit once in a thrips 

 larva. After this, the insect was not again observed to come 

 in contact with thrips larva, so it was very carefully captured 

 and put in 50 per cent alcohol. Later it was sent to the 

 Bureau of Entomology in Washington and determined to be 

 one of the Tetrastichinae. Because of the minute size of this 

 insect it was at once evident that it must be reared from the 

 thrips themselves to bear out the doubtful case of oviposition 

 noted. Therefore it was a source of great gratification to the 

 writer to successfully rear this parasite July 29, from material 

 collected at Hollywood on June 29. This insect is described 

 as a new genus and species on page 233 of these Pro- 

 ceedings by Mr. J. C. Crawford, of the United States National 



