46 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 16 
CHOICE OF FOOD AND NUMERICAL ABUNDANCE AMONG 
INSECTS 
By Charles T. Brues 
Abstract 
Insects are not alone in almost unlimited capabilities for rapid multiplication, the 
limiting causes being prevalence of disease, parasites and available food supply. 
The remarkable instincts associated with the choice of food plants have been largely 
neglected by investigators. Certain insects like the migratory locusts are highly poly- 
phagous, while others are limited to a single food plant, probably through a long 
evolutionary process. Agricultural pests may be either polyphagous, oligophagous 
or monophagous and under primitive conditions the former were represented by 
larger populations than those with more restricted diets. Only very exceptionally 
do natural associations of plants offer ideal conditions for monophagous insects, as 
in western coniferous forests and certain types of grasslands some oligophagous species 
are apparently composed of several phytophagic races propagating more or less 
independently. Species exhibiting remarkable capacity for shifting from one food 
plant to another, such as the cotton boll worm may become extremely abundant 
where its food plants are associated, though natural checks soon establish an approxi¬ 
mate balance as a rule. Trees and plants with a long life cycle occupy a relatively 
insecure position with regard to insect damage. 
In their almost unlimited capabilities for rapid multiplication, insects 
do not stand alone among animals, although the economic entomologists 
may sometimes be tempted to categorize them thus. That many in¬ 
sects frequently approach more nearly the mathematical possibilities 
in their actual population growth than do the vertebrates or even the 
more conspicuous other invertebrates is, nevertheless, quite true, and 
the main contributing causes for this are naturally familiar to the ento¬ 
mologist who is periodically confonted by outbreaks of noxious insects. 
That we may not become too pessimistic concerning the abundance 
of insects, several entomologists have been guilty of counting the pros¬ 
pective progeny of a happily married and economically independent 
pair of insects, able to protect and provide for their descendants during 
a single season. No less an authority than our fellow member Dr. 
Howard assures us that an April bride of our common housefly under 
such ideal conditions would not be able in the autumn to enumerate her 
great grandchildren of the fifth generation with less than 13 figures. 
He further concludes that a really prolific strain of houseflies might pro¬ 
duce a far more extensive family. At that time it did not occur to him 
that even the smaller family, dried and pressed into briquettes, would 
furnish nearly 20,000 tons of a very good substitute for coal, all the prod¬ 
uct of the insignificant fly born at the season of the year when the 
provident members of human society were filling their cellars with 
anthracite. 
