Forest Preserve District of Cook County, Illinois
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Scale Insects and Mealy Bugs
Nature Bulletin No. 404-A   January 30, 1971
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

The insect world contains an enormous number and variety of species but, of them all, the Scale Insects and Mealy Bugs come nearest to being vegetables. Most insects are active animals that fly, hop, scamper, crawl or burrow, but these queer creatures spend most of their lives merely sitting in one spot, sucking plant juices from a branch, twig, leaf, or fruit. Some of our most destructive pests are included among the several hundred kinds of these highly specialized insects. They are so small that the average person seldom realizes that they are responsible for the sickly or dying condition of a tree or shrub. Adult scale insects are extremely variable in shape, and range in size from that of a pinhead up to forms which are a quarter of an inch long. Each hides under a hard protective shell, or scale, of wax secreted by pores on its body, and are frequently so numerous that they form a dense crust. The females molt a few times, and usually discard their legs and wings, before they mature. She lays eggs under the scale and then dies. These hatch into young (called "crawlers") which move around for a period varying from a few hours to a day or two before they settle down and build scales. Unlike the female, the male -always the smaller of the two -- goes through a cocoon stage from which he emerges with a pair of wings but with no means of taking food. He merely mates and dies. Males are scarce In most kinds and in many species have never been seen.

The so-called Soft Scales, or Mealy Bugs, have soft oval segmented bodies powdered with a white waxy secretion, and a fringe of it around their sides. They have small poorly developed legs with which they crawl about sluggishly. The female lays eggs, often several hundred, underneath her body which then becomes a lifeless protective cover for them.

The natural enemies of scale insects and mealy bugs are tiny parasitic wasps, certain flies, lacewings, beetle larvae, and a few infectious diseases. A host of birds feed on them, especially chickadees, titmice, and brown creepers. Most of them were introduced from other countries and they are destructive pests.

The Australian Cottony-Cushion Scale once threatened to wipe out the orchards of orange, grapefruit, lemon and other citrus fruits in California but was brought under control by importing its natural enemies: a red-and-black spotted lady beetle and a fly from Australia. Others are controlled by fumigation with cyanide gas but several have gradually developed resistant strains. The Red Scale, for example, has a race which can "hold its breath" for 30 minutes of treatment. Originally, one minute was enough to kill it.

The San Jose' Scale. probably from China, does not bother citrus fruits but is a serious pest on other fruit trees, shrubs and such trees as elm, oak and walnut. It has tiny round or oval overlapping scales. The Oyster-Shell Scale, with brownish-gray scales resembling miniature oyster shells, infests apple, pear, willow, ash, elm and other trees and shrubs, frequently killing them. The Scurfy Scale and the Cottony Maple Scale -- so called because of the cottony appearance of large egg-sacs on the females -- damage many forest and shade trees in this region .

The Lac Insect has waxy shells which are scraped from certain trees in India and processed to make the shellac of commerce. Another scale insect, the Cochineal Bug, which is a parasite on cactus, has been used since the days of the Mayans and Aztecs to make a beautiful carmine dye. Scale insects are good baby-sitters.

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