Scarcely a plant escapes the little suction pump or beak of some kind of a plant-louse or aphis. More than 300 different kinds of plant-lice have been identified in the United States, and nearly every kind of fruit, flower, farm or garden crop has its special plant-louse enemy, which is often a serious factor in the production of a crop. These little creatures are so small, so variable, so hard to perceive, present so many different forms in the same species, and have such varied and interesting life-stories to tell, that what is known about them is but a mere beginning as compared to what is yet to be learned. It would take a large volume to include the interesting stories which might be told of the lives and of the relations with ants of some of the commonest of these plant-lice. No other group of insects presents so many curious, varied, interesting, and wonderful problems of life as do the aphids. In the aggregate, the damage done by plant-lice is very great.

A crane fly. (Mounted)

Fig. 1319. A crane fly. (Mounted)

A snapping beetle. (Mounted)

Fig. 1320. A snapping beetle. (Mounted)

At times hundreds of acres of peas have been ruined by an aphid. Nursery stock often suffers severely and bearing fruit trees are often seriously injured by them. About forty different kinds of aphides live in greenhouses where a perpetual warfare has to be waged against them. In four years nearly 100 generations of a common aphis have been reared in greenhouses, and there were no indications of any egg-stage or of male forms during this time, so that they may thus breed indefinitely in houses, their young being born alive and no males appearing. The standard remedies for plant-lice are whale-oil soap, kerosene emulsion, and tobacco in various ways (as a decoction, dry as a dust, or in the form of similar extracts), and these are successfully used to kill the aphides in all situations.