Economic Importance
Scale insects are serious plant pests and as small, highly cryptic components of the
plant ecosystem, they frequently are not detected until they have caused significant
damage. They are particularly difficult to detect in quarantine inspections especially
at low population levels. They are most important as agricultural pest of perennial
plants and can cause serious damage to nut and fruit trees, woody ornamentals, forest
vegetation, greenhouse plants, and house plants. Damage is usually caused by removal
of plant sap, but also may be caused by plant pathogens, toxins and the production of
large quantities of honeydew with resultant growth of sooty mold fungi that cover
leaf surfaces and reduce photosynthesis.
Scales also can be beneficial. They have been used as sources of dyes (cochineal
scales, gall-like scales, giant scale, and lac scale), of shellac and lacquerlike
substances (lac scales and giant scales), of candle wax (soft scales), of the manna
of the Israelites (mealybugs), of pearls for necklaces (ground pearls or giant scales),
and even chewing gum (ornate pit scale). Cochineal scales and mealybugs have been
used in the control of noxious weeds.
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