February, ’23] brues: food choice and insect abundance 
47 
It is of course patent that the numerical abundance of a great many spe¬ 
cies of insects, perhaps of nearly all, depends to a very limited extent upon 
their powers of reproduction and almost entirely upon the factors which 
tend to limit these powers. Among these, the prevalence of disease, 
of insect parasites and the extent of the available food-supply are the 
factors that determine how far any species may utilize its latent powers 
for reproduction and multiplication. All three factors are highly vari¬ 
able and to one or the several in combination*may usually be traced 
the numerical abundance of any particular species. Entomologists 
have devoted so much effort toward elucidating the relation between 
host and parasite and the balance between insect and food-plant, that a 
detailed knowledge of such facts is generally recognized as a fundamental 
prerequisite for the formulation of control measures directed against 
agricultural pests. 
In spite of its basic importance in determining the economic status 
of phytophagous insects, the remarkable instincts associated with the 
choice of food-plants have been largely neglected as a field for investi¬ 
gation by economic entomologists, due, no doubt, to the pressing de¬ 
mand for information of more immediate application. 
We know for example, among economic insects of importance that 
some like the various migratory locusts are so highly polyphagous that 
they balk at practically no type of green food (even paris green and 
molasses), while others like the cotton-boll weevil not only refuse, but 
seem actually unable to subsist upon any but a single food plant. These 
two extreme cases suggest that primitive omnivorous insects may have 
become specialized through a long evolutionary process and have pro¬ 
duced among the higher orders first species with restricted diet and 
finally ones of strictly monophagous habits. Such an assumption is, 
in a very broad way, probably correct, but it does not take into account 
the intimate mixture of polyphagous, oligophagous and monophagous 
species to be found in almost any phytophagous division of the higher 
orders of insects. The familiar large Satumiid moths furnish a concrete 
example: the caterpillars of the Cecropia moth are credited with sixty- 
odd food plants, some of course more favored than others, while those of 
the closely related Ailanthus moth are restricted to the ill-smelling 
foliage of the Tree of Heaven, and the Eri silk moth selects almost exclu¬ 
sively the leaves of the castor oil plant. What the reason for such di¬ 
vergencies may be, or whether the Eri caterpillar like the Kansas grass¬ 
hopper would prefer its castor oil with orange juice, I shall not attempt 
to predict in the absence of the proper experimental data, but I wish to 
