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
SCALE INSECTS AND MEALY BUGS
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
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
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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