Scale Insects -- General Information
Scale insects are some of the most unusual insects known. The "adult" females are
sexually mature nymphs that lack wings, the males are insectlike but most live for
a day or less and never feed. Male scales, though part of the Hemiptera which have
incomplete metamorphosis, have their own specially derived form of a complete
metamorphosis with two pupal instars. Scales have the greatest diversity of sperm
structure and sex determining chromosome systems of any known group of organisms.
One group even has a placenta-like structure in the female that is used to feed
first-instar males. This group of insects is so unusual that some scientists have
suggested that scale insects are extraterrestrials.
Scale insects apparently are most closely related to aphids. Adult females are
sacklike with no definite head, thorax, or abdomen, and they may or may not have
legs. The ephemeral males have two pairs of wings, but the hind pair is very small
and is attached to the front wing with one or more setae. Most scale insects produce
a waxy secretion that covers the body either as a domicilelike structure (called a
scale cover) detached from the body or as a substance right on the body surface.
This waxy secretion may vary from a thin translucent sheet to a thick, wet mass or
to a powdery, bloomlike secretion.
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