36 
the straw to break and allow the perfect insect to more readily escape 
from the stem, and the damage done by this insect is chiefly in the 
falling or lodging of the grain which often results from the weaken- 
ing of the straw at the point indicated. Otherwise very little harm 
results, and the heads of attacked wheat are, as a rule, well filled. 
Breeds in wheat.—This insect breeds in wheat in preference to other 
small grains. In fact, it is doubtful whether it often successfully 
develops in other grains than wheat and rye, although the females 
will oviposit in oats and even in the stems of grasses. 
WESTERN WHEAT SAWFLY. 
( Cephus occidentalis Marlatt. ) 
This insect (fig. 23) is in habit exactly similar to the European wheat 
sawfly, and the adult insect closely resembles the European species. Its 
economic importance arises from the fact that it may at any time be 
expected to abandon its native food plants in favor of the small grains, 

Fic. 23.—Western wheat sawfly (Cephus occidentalis): a, larva; b, female sawfly; c, grass stem showing 
work—e, enlarged; a, b, more enlarged (author’s illustration). 
in which it can undoubtedly successfully develop. Such changes in 
the food habits of our native insects are being constantly witnessed, 
as is illustrated by several of the species already discussed’ and the 
leaf-feeding wheat suwflies, which normally affect wild grasses. 
LEAF-FEEDING SAWFLIES. 
As already indicated, several native American sawflies occasionally 
attack growing wheat. These are all species which normally feed on 
wild grasses. The larvee of some half dozen species of the genus Dole- 
rus have been found on wheat. The adult insects of all of these are 
similar, and the species Dolerus arvensis Say (fig. 24) may be taken as 
a characteristic representative of them. It is a blue-black fly, some- 
what larger than the house fly, very sluggish in habit and ordinarily 
found in swampy places on grass in early spring. The larve of these 
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