Aug. 28, 1916 Thersilochus Conotracheli 851 



the; larva 



Position in relation to host. — Throughout most of the larval 

 life this species lives as an internal parasite, the larval parasite lying 

 free within the body cavity of its host. When nearly full grown, how- 

 ever, it leaves the host and becomes temporarily an external feeder, 

 draining from without the last trace of fluid from the body of its victim. 



Feeding period. — Because of the impossibility of following an indi- 

 vidual parasite throughout its development, the determination of the 

 exact duration of the various larval instars is very difficult and must be 

 based on the average of many individuals. During this period of its 

 life the larva molts four times. Larvae of the first instar are to be found 

 within curculio larvae even as long as three days after the latter have 

 finished feeding and entered the ground. In fact, it seems to be the 

 rule that the first larval molt of the parasite takes place after the host 

 has constructed its pupal cell. Apparently, however, this is not invari- 

 ably true, since larvae as old as the third instar have been removed 

 from their hosts within three days of the time the latter entered the 

 ground. Thereafter the development of the parasite is very rapid, for 

 within 10 days it passes through its second, third, and fourth instars, 

 and in some cases has left the body of its host and has begun the con- 

 struction of its cocoon. 



DESTRUCTION OF SUPERNUMERARY LARVAE- 



Repeatedly in the dissection of the parasitized curculio larvae more 

 than one, sometimes several, first-instar larvae of T. conotracheli have been 

 found in a single host. Invariably, however, only one of these was in a 

 healthy condition. The others were mostly dead and more or less 

 inclosed in a mass of cells in the manner described by Timberlake (9, 

 p. 75-76), and shown by him to be amebocytosis. In one case a still 

 living but unhealthy larva partially inclosed by amebocytes was found 

 in a curculio larva that also contained one healthy larva and two dead 

 and completely invested larvae. In no case, however, have all of the 

 parasites been dead. Apparently the death of the parasite larvae is not 

 due to any protective adaptation on the part of the host, as suggested 

 by Timberlake (9), for parasites in strange host species; for, as stated 

 above, in no case were all larvae killed, and in no case where but one 

 egg was deposited within a host was the parasitism unsuccessful. The 

 only source, therefore, of the destructive agency, whatever its nature, 

 must lie within the surviving parasite larva. No explanation as to the 

 nature of this agency is possible at this time. 



