OF WASHINGTON, VOLUME XIII, 1911. 237 



from the body. lu a short time the adult begins to crawl over 

 the foliage in search of host insects. Up to the present time 

 every one of the many hundreds of adults reared have been 

 females and these have reproduced parthenogenetically in all 

 cases observed. In fact, at the present writing two genera- 

 tions have been reared from an unfertilized female. 



The live adult is a beautiful little creature, about 0.60 to 

 0.75 mm. in length, having a black head, bluish black thorax, 

 and hyaline wings; the antennae, legs, and abdomen are light 

 yellow; the posterior part of the abdomen more or less blackish. 



The female parasite, while flying readily when disturbed, 

 on most occasions, crawls over the surface of the leaf very 

 slowly and deliberately or at other times with astounding 

 speed, the antennae in constant motion, first turned to one 

 side and then to the other. When a thrips larva is encoun- 

 tered the hymenopterou stops, then very gently strokes it from 

 end to end with her antennae, and, if satisfied, she bends the ab- 

 domen under her body and exserts an extremely long and slen- 

 der ovipositor. This is deliberately thrust into the body of the 

 thrips larva and in most cases into the side of the abdomen. 

 Generally this process occupies only a few seconds and then the 

 search is continued for other larvae, or in a few cases she re- 

 turns to the same larva and oviposits in it for the second or 

 third time. 



Up to the present writing this insect has been reared in the 

 laboratory from its original host, Heliothripsfasciatiis, from 

 Thrips tabaci (the onion thrips), and from Euthrips tritici 

 (the wheat thrips). Field collections, this past summer (1911), 

 have shown it to be breeding extensively in the onion thrips 

 and bean thrips (Heliothrips fasciatits}, the parasitism in 

 some cases running as high as 70 per cent. The greatest 

 number of adults reared from the eggs deposited by a single 

 female so far has been 91 specimens. 



The time from the laying of the egg until the parasitism is 

 indicated in the host prepupa varies from 6 to 15 days, but is 

 7 days in the greater number of cases. The time required 

 from oviposition to the pupation of the parasite varies from S 

 days in the case of a very few, to 24 days in a few cases, but 

 over 56 per cent change in from 10 to 14 days. The whole 

 life cycle, then, requires from 28 to 48 days, with a mean av- 

 erage temperature of about 65F. The winter is undoubtedly 

 passed in the pupa stage, but the writer hopes to settle this 

 point definitely during the coming winter. 



At present this parasite is known to occur at Compton, 

 Whittier. Puente, and Hollywood, all situated in Los Angeles 

 County. California, and making up an area of nearly 150 

 square miles. As an example of its abundance, Mr. Graf, 



