Lesson XCII

The Colorado Potato-beetle

Leading thought—The Colorado potato-beetle is a very important insect, since it affects the price of potatoes each year. It is disagreeable as a food for birds, because of an acrid juice which it secretes. We should learn its life-history and thus be able to deal with it intelligently in preventing its ravages.

Method—The study of the potato-beetle naturally follows and belongs to gardening. The larvæ should be brought into the schoolroom and placed in a breeding cage on leaves of the potato vine. Other plants may be put into the cage to prove that these insects will only eat the potato. The children should observe how the larvæ eat and how many leaves a full grown larva will destroy in a day. Earth should be put in the bottom of the breeding cage so that the children may see the larvæ descend and burrow into it. The adult beetles should be studied carefully, and especially, the children should see the excretion of the acrid juice.

Observations—1. At what time do you see the potato-beetles? Why are they more numerous in the fall than in the spring? Where do those which we find in the spring come from? What will they do if they are allowed to live?

2. What is the shape of the potato-beetle? Describe the markings on its head. What color are its eyes? Describe its antennæ. How are they constantly used? Can you see the palpi of the mouth? Give the beetle a bit of potato and note how it eats.

3. What is the color of the shield of the thorax? Describe the legs. Do you think the beetle can run fast? Why not? How many segments has the foot? Describe the claws. Describe how it clings to the sides of a tumbler or bottle.

4. If the beetle cannot run rapidly, how does it travel? Describe the wing-covers. Why is this insect called the ten-lined potato beetle?

5. Describe the wings. How are they folded when at rest? How are the wing-covers carried when the beetle is flying?

6. Take a beetle in your hand. What does it do? Of what advantage is it to the insect to pretend that it is dead? If you squeeze the beetle what happens? How does the fluid which it ejects look and smell? Try and discover where this fluid comes from? Of what use is it to the beetle? Why will birds not eat the potato-beetle?

7. Where does the mother beetle lay her eggs? Are they laid singly or in clusters? What color are the eggs? How long after they are laid before they hatch?

8. Describe the young larva when it first hatches. What color is it at first? Does it change color later? Describe the colors and markings of a full grown larva.

9. How does this larva injure the potato vines? Does it remain in sight while it is feeding? Does it act as if it were afraid of birds? Why is it not eaten by birds?

10. Where does the larva go when it is full grown? How many times does it shed its skin during its growth? Does it make a little cell in the ground? How does the pupa look? Can you see in it the eyes, antennæ, legs and wings of the beetle?

11. Write an English theme giving the history of the Colorado potato-beetle, and the reasons for its migration from its native place.