Scale insect

The scale insects are small insects of the order Hemiptera, generally classified as the superfamily Coccoidea. There are about 8,000 species of scale insects.

Most scale insects are parasites of plants, feeding on sap drawn directly from the plant's vascular system. A few species feed on fungal mats and fungi, e.g., some species in the genus Newsteadia in the family Ortheziidae. Scale insects vary dramatically in their appearance from very small organisms (1–2 mm) that occur under wax covers (some look like oyster shells), to shiny pearl-like objects (about 5 mm), to creatures covered with mealy wax. Adult female scales are almost always immobile (aside from mealybugs) and permanently attached to the plant they have parasitized. They secrete a waxy coating for defense; this coating causes them to resemble reptilian scales or fish scales, hence the name.

Scale insects feed on a wide variety of plants, and many scale species are considered pests. Some types are economically valuable, such as the cochineal, Polish cochineal and lac scales. Scale insects' waxy covering makes them quite resistant to pesticides, which are only effective against the first-instar nymph crawler stage. However, scales are often controlled with horticultural oils, which suffocate them, or through biological control.

Female scale insects, unusually for Hemiptera, retain the immature external morphology at sexual maturity. Adult males have wings but never feed and die within a day or two. Male scale insects are unusual in possessing only one pair of wings, thus making them resemble true flies (Diptera), though they lack the halteres (rudimentary hind wings) seen in flies, and have tail filaments, which do not occur in flies. The specifics of their reproductive systems vary considerably within the group, including hermaphroditism and at least seven forms of parthenogenesis.

Treatment

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Gallery

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  A female cottony cushion scale, (Icerya purchasi Maskell) scale with young crawlers

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  Wax scales on a lemon tree branch

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  Scale insect under a laurel leaf

Major families

Superfamily Coccoidea (scale insects)

• cottony cushion scales, giant coccids, and ground pearls (Margarodidae)
• armored scale (Diaspididae)
• cochineal (Dactylopiidae)
• lac scales (Kerriidae, Lacciferidae)
• soft scales (Coccidae)
• pit scales (Asterolecaniidae)
• mealybugs (Pseudococcidae)
• felted scales (Eriococcidae)

Attribution

Much of this article is copied from w:Scale insect under the Creative Commons Attribution-ShareAlike License.

External links

• ScaleNet homepage
• Cottony Cushion Scale: the pest that launched a pest control revolution with photos
• Diaspididae of the World
• Pests & Diseases of Roses
• Scale Insect Forum
• Scales of southerastern U.S. woody ornamentals

on the University of Florida (UF) / Institute of Food and Agricultural Sciences (IFAS) Featured Creatures Web site

• Ceroplastes rubens, red wax scale
• Ceroplastes rusci, fig wax scale
• Coccus viridia, green scale
• Eucalymnatus tessellatus, tessellated scale
• Phoenicoccus marlatti, red date scale