33 



NATURAL ENEMIES. 



The larvae appear to suffer more from the inroads of natural enemies 

 than do those of other species of these insects, perhaps because of 

 their inhabiting- the walls instead of the center of the straws, therel^y 

 rendering- them more accessible. It may be that this is the older form, 

 and a greater number of the parasitic species have become adapted to 

 it as a host insect. There is little doubt that Olujosita ainericana 

 Ashm. and Polyneura citripes Ashm. both attack and destroy the 

 egg's^ as I have reared them in numbers from stems of Elymus inhab- 

 ited by the larvfe, and also the stems of other grasses inhabited by 

 other Isosoma larva?. Eupehiius allynil French, easily known by its 

 slender body, metallic color, with yellow legs, is associated with this 

 as it is with nearh^ all other species of these insects that inhabit the 

 stems of grain and grass. Merisus isosomatls Riley, conspicuous for 

 its yellow body, is almost as abundant as the preceding, and, as the 

 name implies, is parasitic on other species also. Ilomoixn'us chalci- 

 dephagus Walsh is also a parasite, but 1 have reared it in lesser num- 

 bers than the other two, in Illinois, Indiana, and Ohio. Almost the 

 first parasitic species that I reared in connection with the present 

 studies of Isosoma hordei was a second new genus and species, Para- 

 pteromalus isosomatis Ashmead MS. I have myself witnessed the 

 oviposition of all of these parasitic species, and their life histor}^ is 

 probably practically the same. The adults emerge in spring a little 

 later than those of the Isosoma, but there is a second generation of 

 adults in summer, and it is these that I have observed placing their 

 eggs in the cells of I. hordei., thus doubling their effectiveness in hold- 

 ing it in restraint and preventing more frequent and greater devasta- 

 tions in the grain fields of the farmer. While carrying- on the present 

 investigation I have reared an undetermined Eurytoma, a parasite on 

 Isosoma, but as I reared four species of the latter from the same lot 

 of stems, it is impossible to say to what extent it preys upon the one 

 now under consideration, nor do 1 know anything in connection with 

 its habits, except that it makes its appearance in spring, simultaneously 

 with other parasites. 



PREVENTIVE MEASURES. 



The preventive measures might well be summed up under the 

 caption of good farming, for there is not one practical measure but 

 will pay for its carrying out, aside from its entomological influ- 

 ences. As the adults are fully winged and can fl}^ f reeh" from one 

 field to another, less must ])e expected from a rotation of crop, but 

 even under these conditions, a certain amount of benefit will result 

 from a careful system of crop rotation. Wheat, rye, or barley should 

 nev'er be grown on the same land for more than two years in succes- 

 sion without carefully burning over the stubble before preparing the 

 7327— No. 42—03 3 



