Stored-Grain Pests. 43 
not cause injury to grain. On the contrary, they are beneficial, as 
they are attacking and killing the grain weevils and grain moths. 
While parasites kill a large number of 
erain insects, they unfortunately can not 
be considered of great importance from 
the standpoint of grain protection, for 
by the time the grain insects have been 
controlled by parasites the grain itself 
has become very badly damaged. For 
this reason the appearance of a large 
number of parasites in grain cars or ele- 
vators should be disregarded and the 
grain treated as though parasites were 
not present. : 
Grain dealers frequently find a smal] "YS STB com Sap-dectle. 
threadlike white worm* (fig. 64) about ae 
three-quarters of an inch long in grain dust beneath sacks or in the 
bottoms of bins. This is the larva of a small black fly to be found 
crawling upon windows of granaries and flour mills. Because of 
this habit it is called the window-pane fly. Its threadlike larva 
does no harm to grain but is predacious upon the larve of grain pests 
and clothes moths. It is not abundant 
enough to be of value in protecting 
grain. 
HOW GRAIN BECOMES 
INFESTED. 
Grain may become infested in a num- 
ber of ways. It is never possible to set- 
tle satisfactorily litigation over responsi- 
bility for insect damage to grain without 
a thorough knowledge of the history of 
the particular grain shipment involved. 
Several of the worst insect pests of 
grain, notably the Angoumois grain 
moth and the rice or black weevil, fly 
to the grain fields from near-by cribs 
and begin their attack upon the matur- 
ing grain. In the case of wheat and 
similar small grains, the eggs of the insect are laid directly 
upon the heads of grain. In the case of corn the insects can in- 
‘fest only those kernels that are exposed because of poorly de- 
Fic. 61.—Book-louse or psocid. 
45 Scenopinus fenestralis L. 
