Common name

Armored scales or diaspidids

Field characters

Wax covering domicile-like, not attached to body; wax covering with exuviae of 1 or 2 immature instars incorporated and usually visible; cover formed of wax manipulated by pygidium, of solid consistency, not filamentous or powdery; often with ventral cover; body elongate or oval; body color white, yellow, purple, red, or orange; occurring on nearly any part of plant, rare on roots and rootlets; some species become buried under plant epidermis.

Validation characters

Posterior abdominal segment coalesced into wax-forming structure called pygidium; generally with lobes and plates or gland spines on pygidium; legs absent (vestigial in two genera) or represented by small sclerotized area; antennae represented by unsegmented knob; labium 1-segmented.

Notes

This is the most speciose of all scale insect families and because of this, numerous exceptions to diagnostic characters are known. Even so, armored scales are fairly easy to recognize because of the many adaptations that occurred when they became covered by a domicile-like cover. These adaptations mandated changes in feeding habits, elimination of waste, and mating behavior and caused the development of many unique characters primarily associated with cover formation. Diaspididae Targioni Tozzetti was first used as a family by Brues and Melander (1932).

Distribution

Armored scales occur in all zoogeographic regions. Click here for a list of genera and species from the Australasian region, Afrotropical region, Nearctic region, Neotropical region, Oriental region, and Palaearctic region. Diaspidids are most abundant in the Oriental area and least abundant in the Neotropical region.

Hosts

Armored scales have been collected on a diverse array of host plants. Based on an analysis of the host data presented in Borchsenius' catalog (1966), armored scales occur on about 180 families of host plants and nearly 1,400 host genera. The most common host family is Fabaceae with 230 species of armored scales recorded from it. The Poaceae is a distant second with 154 species. The top ten host families are: Euphorbiaceae 145 species; Myrtaceae 138; Rosaceae 124; Moraceae 121; Oleaceae 113; Arecaceae 107; Rutaceae 100; and Lauraceae and Pinaceae each with 99 species. Armored scales generally inhabit hosts that are long lived such as trees and shrubs but occasionally are found on annuals as well. There are surprisingly few species on plant families that include mostly annuals or bienniels such as Asteraceae, Violaceae.

Life history

Diaspidids have 3 female instars and 5 male instars. Life histories are quite diverse; there can be from 1 to 6 or more generations each year and overwintering can be in any instar except the third, fourth, or adult male. Second instars and mated adult females are probably the most common. In many species, the number of generations and overwintering stages can vary depending on the climate. Eggs or first instars are laid under the scale cover and a small slit is present at the posterior end of the cover that allows the crawlers egress to the outside. Scale cover formation is an interesting process that usually involves the incorporation of the crawler and second-instar exuviae. Several groups are pupillarial, i.e., the adult female remains inside of the hardened second instar exuviae. Dispersal is undertaken by the first-instar crawler either passively by air movement or actively by crawling. The first instar is the only life stage that has legs with the exception of the third, fourth, and adult male. Males only incorporate the shed skin of the crawler into their cover; the exuviae of the other instars are kicked posteriorly in the cover.

Important references

Balachowsky 1948b, 1950b, 1951, 1953g, 1954e; Borchsenius 1966; Danzig 1993; Ferris 1937, 1938a, 1941d, 1942; MillerDa2005; AndersWuGr2010; Tang 1986

Diversity

Click here for a check list of all diaspidid genera and species.