CABBAGE-BUTTERFLY
Have a plant of wild mustard or a cabbage growing in a pot. In June, have the pupils, by means of the insect net, catch a number of the white butterflies, the adults of the cabbage-worm.
Place the butterflies in jars or bottles and observe them. Make drawings of them.
Direct the attention of the pupils to the difference between the wings of the male and those of the female. The former has only one dark spot on the front wing, while the female has two spots on this wing.
Release the males and put the females in a vivarium with the potted plant. (A pasteboard box, with a large piece cut out and the opening covered with gauze, makes a good substitute for a vivarium in this case.)
Observe the laying of the eggs. How many are placed at one spot? How are the eggs protected? The eggs may be gathered from the cabbage plants in the garden.
Observe and record the hatching of the tiny worm, its feeding, growth, forming of chrysalis, development into adult.
Frequently little yellow silken cocoons are found in vivaria where cabbage-worms are kept; these are cocoons of a parasite (braconid) that infests the worm.
Because of the ease with which the cabbage-butterfly may be obtained and the rapidity of its development in the various stages, it is very suitable as a type for the study of metamorphosis.
The sulphur, or puddler (called by the latter name because of its habit of settling in groups around the edges of the water holes), is also a suitable type. The larvæ in this case must be fed on clover.
THE TUSSOCK-MOTH
Begin the study of this insect in June and July by observing the larvæ feeding on the foliage of the horse-chestnut and other shade trees, and direct attention to their destructiveness.
In observing the larvæ, note the size, movements, legs, colour, coral red head, tufts of hair on the back, and the three long plumes.
Watch the birds among the trees to discover whether they eat the larvæ.
Of what use are the tufts of hair? Do the larvæ feed by biting or by sucking? Describe the damage done by the larvæ.
Collect a number of these larvæ and place them in the vivarium with some twigs of horse-chestnut. Observe the spinning of the cocoon and, about two weeks later, look for the emergence of the adult moths.
Observe the two kinds of insects. Describe each. Are there any differences in the cocoons from which they emerge?
Which form of insect places the egg mass and is therefore the female? Note the number and shape of the eggs and how they are protected.
The female moths have no wings and do not move far from the cocoons from which they emerge, while the males have the power of flight.
As outdoor work, look for the egg masses on trees and fences and devise means of combating the tussock-moth.
Gathering and destroying the egg masses during the winter is found to be fairly effective in checking these insects. Since the cocoons frequently contain parasites that prey upon the larvæ, it is advisable that only the cocoons that have egg masses attached to them should be destroyed; the others are harmless and may contain the useful parasites.
The egg masses may be kept over winter in a box in a cool place, and the hatching of the tiny larvæ and their subsequent rapid growth observed.
POTATO BEETLE
The eggs of this beetle may be found in early summer in clusters on the under surfaces of the leaves of potato plants.
Egg.—Observe the size, colour, shape, position, and number in a cluster; appearance of head from outer end after a week.
Larva.—Observe the colour, shape, head, legs, voracious appetite, movements, rapid growth, destructiveness.
Pupa.—Observe the larvæ disappear from the plants; a search underground reveals the resting stage, or pupæ. After ten days, the adult beetles emerge.
Adult.—Observe the colour, the hard shell covering the head; the hard outer wings and membraneous inner wings; the hard shell on the under surface of the body; the feelers, and legs.
Why will spraying with a poison, such as paris-green, kill these insects?
REFERENCES
Dearness: How to Teach the Nature Study Course Stories in Agriculture, Bulletin No. 124.