22 



NATURAL ENEMIES. 



Probabh' the mo.st efficient enemy of this species is a small, slender, 

 four- winged fly, of somewhat brilliant metallic-colored body and yel- 

 low legs. This has a very slight resemV)lanco to an Isosoma, and, 

 indeed, was descril)ed as Isosoma (dlynl!^ now known as EujM'hnus 

 (dJynii French. A somewhat similar insect with metallic body and 

 yellow abdomen, Sflctonotus-isosoiiiatls Kiley, is ver}' efficient in destroy- 

 ing the larva? in the straw. Iloiiiojxrrns {Serniotellns) cludv'tde^thagus 

 Walsh and beyond a doul)t other chalcids are also instrumental in hold- 

 ing it in check. These parasites are all the more 

 efficient as they are doul)le-l)rooded also, developing 

 in late summer and at once ovipositing in other larvse. 

 There is also an o^^^ parasite that 1 have reared in 

 connection with Isosoma, but not with certaint}" from 

 this species. This is OJlgosHa americana Ashmead 

 MS. As in all cases where I have obtained this there 

 were species involved other than the one under con- 

 sideration, it is obviously impossible to say that it 

 destroys the eggs of this species, but w^ith such regu- 

 larity does it occur in connection with Isosoma in 

 Fig. 7.-^^Pedicuioides general that no doubt it preys upon this one with the 

 wK^nposHs Ncwp., a others. Whcu the wheat is harvested the straw is 

 the larva — much frequently, and, in fact, almost invariably, cut off 

 enlarged (after Mar- between joints, thus leaving the larvffi, if there are 

 such in the straws at that point, exposed to attack 

 from predaceous insects. The larva? of a small, slender, l)lack and 

 yellow carabid beetle {Leptotrachelus dorsal is Fab.) crawls up, 

 descends into the stubble and devours the Isosoma larva^, but unfor- 

 tunately its taste seems to be too obtuse to allow it to confine itself 

 strictly to Isosoma, and as a consequence it devours parasites as well 

 as host. The mite Pedlculoides {Heteropus) ventricosus (fig. 7) is also 

 an enemy, gaining access to the larvre precisely as with the beetle 

 larvse previously mentioned. 



PREVENTIVE AND REMEDIAL MEASURES. 



The fact of the spring brood being almost entirely wingless and 

 therefore unable to fl}' from field to field places it almost totally at the 

 mercy of the farmer, as he has Ijut to change his crop from one field 

 to another to rid himself of its presence. It is true the summer form 

 can fly about from field to field at will, and it does so, but if the spring 

 brood of adults are left helpless in a field with no wheat plants in which 

 to place their eggs, it will be seen at once that there can be no sum- 

 mer brood emanating from this source. Rotation of crop will as a 

 consequence be sufficient to prevent an overabundance of this species. 

 But there are conditions under which this is not practicable, as in some 



