February, '17] PHILLIPS: ISOSOMA INVESTIGATIONS 145 



Although the different species of Isosoma refuse to accept a sub- 

 stitute for their own particular host their parasites are not so con- 

 servative, several of the more important ones being very cosmopolitan 

 in their tastes. Thus it will be seen that the majority of the Isosoma 

 are of either direct or indirect economic importance, since a parasite 

 can much more easily maintain itself where there are a number of 

 convenient hosts available. 



A long list of parasites have been reared from Isosoma, the majority 

 of which are new. The life histories of only a few of these parasites 

 have been worked out in any detail. One of the most interesting ones 

 thus far encountered is Eurytoma pater n. sp. The larva is a true 

 parasite in its early stages, the final stage being completed on plant 

 tissue. The parasite pierces the small tender gall and places its egg on 

 the Isosoma larva. When the egg hatches the host larva is about a 

 fourth to a third grown. By the time the parasite consumes the 

 Isosoma larva it is scarcely a third grown and the only alternative is 

 for it to finish its development on plant tissue, which at that time is 

 very soft and succulent. These larvae do complete their development 

 in the same Isosoma cell, since they seem incapable of migrating to 

 nearby cells to prey upon other larvae. Therefore, as stated previously, 

 it seems that they must and do complete their development on plant 

 tissue. 



The most important parasites of I. tritici are undoubtedly Ditro- 

 pinotus aureoviridis Cwfd. and Homoporus chalcidophagus Walsh. 

 There are two others, Eurytoma pater n. sp. and Eurytoma bolteri 

 Riley var. parva n. var., are probably next in importance. Immense 

 numbers of /. tritici are killed nearly everj^ winter by extreme cold. 

 Another active agency in the control of /. tritici is a tinj^ mite, Pedi- 



Plate 8 

 Isosoma breeding cage with door closed. 

 Isosoma breeding cage with door open. 

 Pot cage for Isosoma breeding. 

 Isosoma breeding Experiments at Charlottesville, Va. 



Plate 9 

 Sheath dissected from the head of wheat, showing the galls in the sheath 

 and not in the stem. 



Shows typical galls of the species that forms galls in the sheath surround- 

 ing the heads of wheat. 



Typical galls of Isosoma tritici in wheat. Note that the galls are in the 

 stem itself. 



Plants showing typical injury from the species that forms galls in the 

 sheath surrounding the head. 

 A gall-forming Isosoma inserting ovipositor. 

 A gall-forming Isosoma ovipositing. 



