Steve Adamson, age 13, of Champaign, I11., for his question:
ARE THERE MANY KINDS OF SCALE INSECTS?
A scale insect is one of many kinds of sucking insects that feed on plants. There are more than 2,000 kinds of scale insects and over 400 of them live in the United States and Canada.
Scale insects cluster on plants, sucking out the juices through their tiny, tubelike beaks. They may weaken a plant so much that it dies. '
The female scale insect does the damage. The adult male has no mouth and cannot feed. It only lives long enough to fertilize the female's eggs.
Most kinds of female scale insects are oval shaped. They measure from 0.04 to one inch long, depending on the species.
The creature gets its name from the waxy or scaly shell that covers its body. Some kinds of scale insects hardly look like insects at all. They don't have eyes, feelers or legs and they stay in one spot for most of their lives.
The San Jose scale is one of the best known and most harmful of all the scale insects. It is extremely destructive and found on shrubs and fruit trees in all parts of the U.S. and Canada. The pest is no larger than the head of a pin. Branches of infected trees are often powdered with millions of their tiny bodies. The plants look as if they have been completely coated with ashes.
The San Jose scale was discovered in 1880 in San Jose, Calif. Prior to that time it didn't exist in North America. It is believed to have been introduced on trees that had been brought from China. The San Jose scale was not found east of the Rocky Mountains until 1893, but by 1895 it had spread across the nation and into Canada.
The tiny insect strikes such plants as fruit trees, members of the rose family, the pecan, the English walnut and the elm. Apple and pear trees are the fruit trees most often hit.
Another common and pesky scale insect is the mealybug. It often attacks fruit trees. Mealybugs are usually covered with a secretion that is powdery, sticky and waxy.
One scale insect, called the cottony cushion scale, seemed likely at one time to wipe out all the citrus trees in California. But in 1890 a scientist found an Australian species of ladybird beetle which fed on the cottony cushion scale. The beetles were let loose in the orchards and in a short time they saved the citrus growers from ruin.
Some scale insects are useful to man. Shellac, a varnish, comes from the lac scale. Cochineal, a dye, comes from the cochineal scale.
One kind of scale insect is used as jewelry. It lives on roots and covers itself with shells called ground pearls.
Natural cochineal dye is made from the fried bodies of the tropical scale that is native to Mexico and Central America. They also live in Spain, Algeria and Java. The insects feed on cactus plants. The bodies of 70,000 insects yield only one pound of dye. Coal tar dyes, however, have largely replaced cochineal to produce crimson, carmine and scarlet.