AN INTERNAL PARASITE OF THYSANOPTERA. 39 



was noted tliat oviposited on the first and eighth chiy while confined 

 in a vial with lavvve of TJirips tahaci, at Washhigton, D. C. This 

 oviposition period undoubtedly is shorter than that which occurs 

 under conditions which are normal, for, confined in the vials, the 

 V parasites were in close contact with many thrijis larvae, their eventual 

 hosts, and so might deposit their eggs faster, while in the open field 

 the parasites were compelled to spend considerable time in searching 

 among the leaves for the thrips larvae. Undoubtedly this alone 

 would lengthen the normal period of oviposition to at least double 

 that over which oviposition was observed to occur under artificial 

 conditions in the laboratory. 



DOUBLE PARASITISM. 



Altliough it has been frequently observed that this parasite would 

 oviposit in the same host two or even three times, only one adult 

 hymenopteron has ever been reared from these doubly-parasitized 

 specimens, and in nearly every case only one parasitic larva has 

 seemed to develop in them. On one occasion, however, Mr. Graf, 

 late in November, 1911, observed a case in wliicJi double parasitism 

 had developed and under such conditions that its success was plainly 

 indicated. At that time he took the following notes: 



In the prepupa that was doubly parasitized, the parasitic larva occupying the 

 abdomen of the thripB was about fuU-nized and no great difference in size could be 

 noted in the alimentary canal of this one as compared with the other.-^. The second 

 paranilic larva occupied the thorax of the host prepupa, with one end of its body 

 against one anterior angle of the thorax of the host, while the other end was agamst 

 the opposite posterior angle. The colored portion was about one-fourth natural size, 

 and it was more of a yellowish red. It was well shaped however, and not in the 

 least distorted by its position. Under the high-power lens there was a plain division 

 between the two and there was no mistaking the fact that there were two distinct 

 hymenopterous larvae occupying the body of the prepupal host at the same time. 

 Judging from the appearance under the lens, tt^e larva occupying the abdomen of 

 the host would have been able to develop and pupate, while the one located in the 

 thorax, due to its cramped position and inadequate food supi)ly, would have been 

 unable to reach the pupating stage and would have died. 



Unfortunately this host was killed so that no data were obtained 

 as to whether either of the parasitic larvae would have been able to 

 complete its transformation. However, double parasitism must 

 always result in the death of one of the larvae and in such a small 

 host undoubtedly in many cases both must die owing to the insullicient 

 nourishment afforded by such a minute host. 



ACTIVITY. 



Wliile the adult parasite is usually quiet, during the period just 

 after emerging from the pupal case it is, under normal conditions, 

 Uke most of the Hymenoptera, a veiy active insect. At times it has 



