Lesson LXXXVII

The Aphids, or Plant-lice

Leading thought—Aphids have the mouth in the form of a sucking tube which is thrust into the stems and leaves of plants; through it the plant juices are drawn for nourishment. Aphids are the source of honey-dew of which ants are fond.

Method—Bring into the schoolroom a plant infested with aphids, place the stem in water and let the pupils examine the insects through the lens.

Observations—1. How are the aphids settled on the leaf? Are their heads in the same direction? What are they doing?

2. Touch one and make it move along. What does it do in order to leave its place? What does it do with its sucking tube as it walks off? On what part of the plant was it feeding? Why does not Paris green when applied to the leaves of plants kill aphids?

3. Describe an aphid, including its eyes, antennæ, legs and tubes upon the back. Does its color protect it from observation?

4. Can you see cast skins of aphids on the plant? Why does an aphid have to shed its skin?

5. Are all the aphids on a plant wingless? When a plant becomes dry are there, after several days, more winged aphids? Why do the aphids need wings?

6. Do you know what honey-dew is? Have you ever seen it upon the leaf? How is honey-dew made by the aphids? Does it come from the tubes on their back? What insects feed upon this honey-dew?

7. What enemies have the aphids?

8. What damage do aphids do to plants? How can you clean plants of plant-lice?

I saw it (an ant), at first, pass, without stopping, some aphids which it did not however disturb. It shortly after stationed itself near one of the smallest, and appeared to caress it, by touching the extremity of its body, alternately with its antennæ, with an extremely rapid movement. I saw, with much surprise, the fluid proceed from the body of the aphid, and the ant take it in its mouth. Its antennæ were afterwards directed to a much larger aphid than the first, which, on being caressed after the same manner, discharged the nourishing fluid in greater quantity, which the ant immediately swallowed: it then passed to a third which it caressed, like the preceding, by giving it several gentle blows, with the antennæ, on the posterior extremity of the body; and the liquid was ejected at the same moment, and the ant lapped it up. Pierre Huber, 1810.