Scale insect

Scale insects are small organisms belonging to the order Hemiptera. They are part of the infraorder Coccomorpha. This group is known for having a very wide range of appearances. They also show extreme sexual dimorphism, which means males and females look very different. There are approximately 8,000 described species in this group.

These insects are important to many different fields. Some are considered serious commercial pests. Others provide materials for industry, such as dyes and lacquers.

Scale insects feed as herbivores by using specialized mouthparts. They pierce plant tissues to suck out the sap.

As they drink this excess fluid, they secrete a sugary substance called honeydew. This liquid can cause a black sooty mold to grow on the plant. Many scale insects live in a mutualistic relationship with ants. The ants feed on the honeydew. In exchange, the ants protect the scale insects from predators.

The life cycle of a scale insect begins with the eggs. Once they hatch, the young are called "crawlers" or first instar nymphs. These crawlers are the only mobile stage for most species. They crawl around to find a good place to settle and feed.

Once they find a spot, most females become sedentary. This means they stay in one place for the rest of their lives. Many females even lose their legs after they moult. They grow a waxy coating for defense. This wax can make them look like tiny shells or fish scales.

Female scale insects are often characterized by neoteny. This is a condition where they retain their immature physical traits even as adults. They are often pear-shaped, circular, or elliptical. They lack wings and often lack compound eyes. Instead, they may have ocelli, which are simple eyes. Some families, like Beesoniidae, do not even have antennae.

In contrast, adult males look like small flies or aphids. They have functional legs and often have wings. Most males do not eat at all. They emerge, find a female, and die within two or three days.

The genetics of scale insects are incredibly complex. Many species use parthenogenesis, which is a form of asexual reproduction. Some species also use paternal genome elimination, or PGE. In this process, the male's genetic material is removed during development. This happens in nearly 14 different scale insect families. There is also a rare form of hermaphroditism. In the genus Icerya, individuals possess an ovotestis. This organ contains both male and female reproductive tissues.

Scale insects have a very long history on Earth. The oldest fossils are found in amber from the Late Jurassic period. By the Early Cretaceous, they were already very diverse. This suggests they may have originated as far back as the Triassic.

They are closely related to other insects like aphids, whiteflies, and jumping plant lice. Their ability to adapt to different plants has helped them succeed. Some species are monophagous, meaning they eat only one plant type. Others are polyphagous, meaning they can feed on many different plant groups.

These insects have significant impacts on human economy and ecology. The cottony cushion scale is a major pest for Citrus fruit trees. It is hard to control because its waxy covering protects it from insecticides. However, some species are used for biological control. For example, they can be used to manage the prickly pear plant. Scale insects also produce valuable substances. They are used to make shellac lacquer. They also produce red dyes known as carmine and kermes. The names for colors like crimson and scarlet actually come from these insect products.