Introduction to Scale Insects
Scale insects are a diverse group of insects in the order HOMOPTERA. There are about 6,000
species of scale in sects in 21 families worldwide. About 1,000 species occur in North America.
The three most common families of scale insects are the armored scale, the soft scale, and the
mealybugs. Most of the pest species belong to one of these three families.
Armored Scale Insects- Armored scales are the smallest of scale insects, ranging in size from 1 to
3 mm. The body of the scale insect is protected by a cover (the armor) made from wax secreted by
the insect and cast skins (exuviae) of previous growth stages. One must remove the hardened wax
cover to expose the body of the insect. The exposed body usually is yellow or orange, but may
have a pink or red color to it. This cover also protects the eggs laid by the female. Armored scale
insect covers vary from circular to elongate or oystershell-shaped (Fig. 115). Male and female
covers may differ in size and shape for the same species. The cover of the female is generally
largest. Boisduval scale and fern scale are common armored scale insects attacking flowers and
foliage plants.
Most armored scale insects reproduce sexually. The eggs hatch beneath the protective scale cover
and the first instars, commonly called "crawlers", migrate to the new growth to settle and feed.
Armored scale females lose their legs at the first molt and are sessile for the rest of their lives.
Females develop through three instars and males develop through five. Armored scales may
overwinter as eggs, nymphs, or adult females. Adult males are usually present about two weeks in
each generation. Some armored scales have four generations per year.
Soft Scale Insects- Soft scales (Fig. 116) differ from armored scales in that they do not secrete a
waxy covering that is separate from the body. If wax is present, it adheres tightly to the body of the
female and cannot be easily separated from it. Most soft scales produce a thin, glassy wax that
does not obscure the color or form of the female soft scale. Soft scales are fairly large (2 to 6 mm
long) and can be distinguished by their larger size, round or oval body outline, and convex or
hemispherical profile. Soft scale females vary from flat to almost spherical. Often different host
plants will alter the body form of a single species so much that taxonomists have described the
different forms as separate species. If one turns the adult soft scale over, legs, antennae and
thread-like mouthparts are readily visible with the aid of a microscope. Three common soft scales
found in greenhouses and interior plantscapes are the brown soft scale, hemispherical scale, and
tessellated scale.
Soft scales may reproduce sexually or parthenogenetically and every female may be capable of
producing progeny without fertilization. Tremendous populations can develop during a single
growing season. Most out door species have one generation per year. Females either lay eggs or
give live birth, depending on the species. There are three instars in the females and five instars in
the males. In warmer climates and in greenhouses, species with multiple generations may have all
stages present simultaneously throughout the year.