194 INSECTS AFFECTING VEGETATION 



grains than wheat and rye, although the females will oviposit in oats 

 and even in the stems of grasses. 



Western Wheat Sawfly. This insect 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, in which it can undoubtedly success- 

 fully develop. Such changes in the food habits of our native insects 

 are being constantly witnessed, as is illustrated by several of the spe- 

 cies already discussed and the leaf-feeding wheat sawflies, 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 larvae of some half 

 dozen species have been found on wheat. The adult insects of all of 

 these are similar, and the species may be taken as a characteristic 

 representative of them. It is a blue-black fly, somewhat larger than 

 the house fly, very sluggish in habit and ordinarily found in swampy 

 places on grass in early spring. The larva? of these insects attain a 

 length of nearly an inch, are usually dull or dirty whitish in color, 

 with the head marked with brown. Some of them are also marked 

 with brown stripes or spots along the side of the body. They occur, 

 as a rule, singly, and are rarely in sufficient numbers to be of any 

 economic importance. 



Grass Sawfly. A more important species is a grass sawfly about 

 the size of a common house fly, which occurs throughout the North- 

 ern States east of the Rocky Mountains. The eggs of this insect are 

 inserted in rows along the edge of the blade of wheat, or more com- 

 monly in grasses, and the larva? hatching from these feed on the 

 leaves more or less gregariously while young. As they become full 

 grown they separate and become practically solitary feeders. They 

 may be distinguished from the latter, however, by being uniformly 

 yellowish green in color, with the head similarly colored, with the 

 exception of the two minute brown eyespots, and by the possession 

 of seven instead of eight pairs of abdominal feet. 



This species, also, can scarcely be considered as having great 

 economic importance. So far as they work on the leaves of the wheat 

 their damage is inconsiderable, but occasionally they are attracted 

 by the green portion of the stem just below the head, especially as 

 the wheat ripens, and sever the stalk at this point, causing consider- 

 able loss. 



The fact that damage from both the stem-boring and leaf-feed- 

 ing sawflies has never been very considerable in this country has 

 made it unnecessary to adopt any special precaution with regard to 

 them. Where land is deeply plowed and replanted in the fall both 

 the stem borers and the leaf feeders will be buried too deeply to es- 

 cape. The only danger, therefore, comes from land that is left in 

 stubble over winter or long enough for the adult insects to emerge in 

 spring. Should any of these insects ever assume any especial im- 

 portance, they can doubtless be kept in easy control by seeing that 



