ise it sunk half-way in the commencement of a burrow, at
the mouth of which is a white floury powder, the waste from the
mandibles. It works its way inward and buries itself in the heart of the
seed. It will emerge in the adult form in the course of about five
weeks, so rapid is its evolution.

This hasty development allows of several generations in the year. I have
recorded four. On the other hand, one isolated couple has furnished me
with a family of eighty. Consider only the half of this
number--supposing the sexes to be equal in number--and at the end of a
year the couples issued from this original pair would be represented by
the fortieth power of forty; in larvae they would represent the frightful
total of more than five millions. What a mountain of haricots would be
ravaged by such a legion!

The industry of the larvae reminds us at every point what we have learned
from the _Bruchus pisi_. Each grub excavates a lodging in the mass of
the bean, respecting the epidermis, and preparing a circular trap-door
which the adult can easily open with a push at the moment of emergence.
At the termination of the larval phase the lodgements are betrayed on
the surface of the bean by so many shadowy circles. Finally the lid
falls, the insect leaves its cell, and the haricot remains pierced by as
many holes as it has nourished grubs.

Extremely frugal, satisfied with a little farinaceous powder, the adults
seem by no means anxious to abandon the native heap or bin so long as
there are beans untouched. They mate in the interstices of the heap;
the mothers sow their eggs at random; the young larvae establish
themselves some in beans that are so far intact, some in beans which are
perforated but not yet exhausted; and all through the summer the
operations of breeding are repeated once in every five weeks. The last
generation of the year--that of September or October--sleeps in its
cells until the warm weather returns.

If the haricot pest were ever to threaten us seriously it would not be
very difficult to wage a war of extermination against it. Its habits
teach us what tactics we ought to follow. It exploits the dried and
gathered crop in the granary or the storehouse. If it is difficult to
attack it in the open it would also be useless. The greater part of its
affairs are managed elsewhere, in our storehouses. The enemy establishes
itself under our roof and is ready to our hand. By means of insecticides
defence should be rela