AN INTERNAL PARASITE OF THYSANOPTEEA. 



41 



tion was veiy slow on leaves of the latter type and the percentages 

 of thiips larvai parasitized in such experiments were low. Without 

 doubt this same difficulty arises in nature, so tliat thrips living on 

 plants with spmy or sticky leafage will not be so highly parasitized 

 as those living on plants with smooth leafage. 



HOST RELATIONS. 



Heliothrips fascialus Pers;ande. 



The parasite in question, Thripoctenus russelli Crawford, was 

 first discovered in "the larvae of Heliothrips fascialus Pergande, and 

 when the adult ])arasites were first reared they were naturally con- 

 fined in vials, with the young of this species, and at once oviposited 

 in them. These were carefully manipulated and the parasites later 

 reared in large numbers under laboratory conditions. Collections 

 of this thrips made at various times during 1911 have shown it to be 

 regularly parasitized by this hymenopteron. 



Thrips tabaci Lindemaii. 



As soon as oviposition was noted in larva? of Heliothrips fascialus, 

 larvae of the onion thrips (Thrips tabaci Lindeman) were substituted 

 for those of Heliothrips as a possible host for the parasite, with the 

 result that oviposition took place at once. From these onion thrips 

 larvae the parasites were successfully reared in large numbers. On 

 September 2, 1911, this parasite was observed actively ovipositing 

 in lai-vse of Thrips tabaci in the field and from collections of lai'vse 

 of this species made at that time the parasite was reared in large 

 numbers. (See Table III.) 



Table III. 



-Parasitism of Thrips labaci as shown by field collections at Compton, 



C'al, 1911. 



The percentage of ])arasitism of this species in September, 1911, 

 ranged in different collections from 15 per cent to 00 per cent, while 

 the average of 7 lots was 33.5 per cent, as shown in Table IV. 



