1930 ] 
The Food of Insects 
7 
the insects concerned as polyphagous, oligophagous and 
monophagous, respectively. 
The labors of economic entomologists have gone far to- 
ward an elucidation of the interactions of these several 
types of food-habits as they determine the competition for 
food among insects and the devious ways in which they in- 
fluence the bioccenotic relations of insect food plants. And, 
since no plants appear to be immune to insect attack this 
question is seen at once to involve the whole terrestrial flora. 
Several factors concerned in these relationships between 
insects and plants may be considered separately. The effect 
of insect feeding on the flora is by no means the same in the 
case of polyphagous, oligophagous and monophagous spe- 
cies. With the former a long series of plants suffer to a 
more or less equal degree. Thus, with grasshopper out- 
breaks there is general injury to all kinds of vegetation; 
with the gypsy moth a considerable series of trees and also 
other plants suffer, but not to an equal extent. This means 
that there is a simultaneous reduction in the abundance of 
a number of different plants, and an opportunity is offered 
for many others to increase, at least temporarily, while 
many competing insects decline due to a lessened food sup- 
ply. Thus, in brief, outbreaks or fluctuations among poly- 
phagous species involve many other insects and plants to 
a major extent. We can also see how such feeding might 
actually cause the extinction of certain rare or poorly 
adapted plants. 
The feeding of oligophagous insects results in the injury 
to a greatly restricted series of plants and has, of course, 
no direct effect upon any others. If dominant species of 
plants be affected there as a very considerable opportunity 
for many rarer forms to increase, while if a reverse con- 
dition prevails and the scarcer forms are affected, the in- 
fluence upon the remainder of the competing flora is negli- 
gible. Incidentally we must notice that the extinction of 
certain plants might result from the feeding of oligopha- 
gous species, although the chances for such an occurrence 
are less than those noted above in the case of polyphagous 
insects since a great reduction in one of a few food plants 
will at once considerably reduce the food supply. This is 
then immediately reflected in a lesser abundance of the in- 
