The conclusion to be drawn from these facts is obvious:  the young and tender haricot is not the proper diet.  Unlike the Bruchus pisi, the female of the haricot-weevil refuses to trust her family to beans that are not hardened by age and desiccation; she refused to settle on my bean-patch because the food she required was not to be found there.  What does she require?  Evidently the mature, dry, hard haricot, which falls to earth with the sound of a small pebble.  I hasten to satisfy her.  I place in the bottles some very mature, horny pods, thoroughly desiccated by exposure to the sun.  This time the family prospers, the grubs perforate the dry shell, reach the beans, penetrate them, and henceforth all goes well.

To judge by appearances, then, the weevil invades the granary.  The beans are left standing in the fields until both plants and pods, shrivelled by the sun, are completely desiccated.  The process of beating the pods to loosen and separate the beans is thus greatly facilitated.  It is then that the weevil, finding matters to suit her, commences to lay her eggs.  By storing his crop a little late the peasant stores the pest as well.

But the weevil more especially attacks the haricot when warehoused.  Like the Calander-beetle, which nibbles the wheat in our granaries but despises the cereal while still on the stalk, it abhors the bean while tender, and prefers to establish itself in the peace and darkness of the storehouse.  It is a formidable enemy to the merchant rather than to the peasant.

What a fury of destruction once the ravager is installed in the vegetable treasure-house!  My bottles give abundant evidence of this.  One single haricot bean shelters a numerous family; often as many as twenty members.  And not one generation only exploits the bean, but three or four in the year.  So long as the skin of the bean contains any edible matter, so long do new consumers establish themselves within it, so that the haricot finally becomes a mere shell stuffed with excreta.  The skin, despised by the grubs, is a mere sac, pierced with holes as many as the inhabitants that have deserted it; the ruin is complete.

The Bruchus pisi, a solitary hermit, consumes only so much of the pea as will leave a cell for the nymph; the rest remains intact, so that the pea may be sown, or it will even serve as food, if we can overcome our repugnance.  The American insect knows nothing of these limitations; it empties the haricot completely and leaves a skinful of filth that I have seen the pigs refuse.  America is anything but considerate when she sends us her entomological pests.  We owe the Phylloxera to America; the Phylloxera, that calamitous insect against which our vine-growers wage incessant war:  and to-day she is sending us the haricot-weevil, which threatens to be a plague of the future.  A few experiments gave me some idea of the peril of such an invasion.

For nearly three years there have stood, on my laboratory table, some dozens of jars and bottles covered with pieces of gauze which prevent escape while permitting of a constant ventilation.  These are the cages of my menagerie.  In them I rear the haricot-weevil, varying the system of education at will.  Amongst other things I have learned that this insect, far from being exclusive in its choice, will accommodate itself to most of our leguminous foods.