About the keys

Tips for using the scale keys

A potential problem with keys that do not contain all species in a genus is the possibility of a "false positive." For instance, if your specimen has not been is an infrequently intercepted at U.S. ports of entry and is not included in the keys or is a new interception that shares all the character states with a species that is in the key, you may arrive at an incorrect identification of your specimen. For this reason, it is very important to compare the specimen at hand with the descriptions provided in the fact sheets and with the drawings. If any question remains regarding the identification of the specimen, a specialist should be consulted.

Scale families

The following characters will assist in determining if an unknown insect is a scale insect: Scale insects are characterized by having a single claw on each leg, neotenic adult females, winged but non-feeding adult males, and an unusual form of metamorphosis that normally includes a prepupa and pupa in the adult male. Other Sternorrhynchous insects have 2 claws on each leg. Generally scales have 3 or 4 instars in the female and 5 instars in the male. Most scale insects produce some kind of wax covering that may entail a mealy substance over the body or elaborate waxy structures that are attached to the body of the insect or are formed as domicile-like structures.

The scale families key was built to help identify all known families of scale insects. Even though there is some disagreement about the status of a few of these families, this list is consistent with the hypotheses of most coccidologists. A list of the families included can be found on the fact sheet index page.

Mealybugs key

This key was built to help identify species in three closely related scale insect families that were previously included in the Pseudococcidae or mealybugs. The families included are mealybugs (Pseudococcidae), giant mealybugs (Putoidae), and ground mealybugs (Rhizoecidae). The species included were selected because they were intercepted more than five times at U.S. ports-of-entry between 1995 and 2012, or are considered likely threats for introduction.

When you first open the mealybugs and mealybug-like families key, you will be prompted to choose the family your specimen belongs to (in order to use this key, you MUST KNOW the family classification of your specimen. If you do not know this, please go to the scale families key, and key your specimen out to family.)

Soft scales key

This key was built to help identify pest soft scale insects (Coccidae). The following combination of characters will assist in determining if an unknown scale insect is a soft scale: with two anal plates located lateral of the anal opening; with an anal cleft; usually with stigmatic setae that are differentiated from other marginal setae; tubular ducts, when present, invaginated. Additional information about soft scales can be found here. The species included were selected because they were intercepted more than five times at U.S. ports-of-entry between 1995 and 2012, or are considered likely threats for introduction.

Soft scales (or coccids) in the field are diverse in habit, color, shape, and form. They occur on leaves, stems, and branches of their host and may occasionally be found on fruit or roots. Although woody plants are the most important hosts, perennial grasses and herbaceous plants are not immune to soft scale infestation. Most species have a flat ventral surface that adheres tightly to the host substrate and a slightly to highly convex dorsum. When the adult female is removed from the substrate, a pair of white wax bands can usually be seen on the host and the venter of the soft scale. These bands are formed by the wax-pores in the spiracular furrows. The body usually lacks a visible wax covering, although species in the genus Ceroplastes produce a variety of ornate waxy covering. Examination of the posterior end of the body with a hand lenses or dissecting microscope will reveal the presence of anal plates, which are diagnostic of the family. Females of most species lay their eggs under their bodies, but females in a few genera, such as Pulvinaria, produce a conspicuous ovisac behind and beneath their bodies.

Many soft scales are serious pests, particularly as invasive species. In the United States there are 42 introduced species of soft scales and 41 of them are pests (Miller and Miller 2003). Species such as the brown soft scale, Florida wax scale, Mediterranean black scale, hemispherical scale, European fruit lecanium, and nigra scale are serious pests not only outdoors, but also in greenhouses and internal landscape environments.

Soft scales occur in all zoogeographical regions of the world. The family is most speciose in the Palearctic region, and least speciose in the Neotropical area. There are slightly more than 1,100 species of soft scales worldwide.

Soft scales have 3 or 4 female instars and 5 instars in the male. Life history data are highly variable throughout the Coccidae. In the United States many species have one generation each year, although two generations is not uncommon. Greenhouse pests may have as many as six generations each year. Some tropical species develop continuously throughout the year but slow their growth rate during cooler or drier periods. Overwintering may occur in any stage except the third, fourth, or fifth instar male. Most species overwinter in the same stage; second instars and mated adult females are the most common overwintering stages for species in the United States. Either eggs or first instars may be laid by the adult. Most species produce large numbers of offspring; some species of Ceroplastes are reported to lay 2,000 or more eggs. In many instances the first instars settle on the leaves. Immature females usually continue to feed on the leaves until late summer or early fall, at which time they move to the stems or branches of the host. Parthenogenesis is common in soft scales, although some parthenogenetic forms may produce a small percentage of males.

There is a total of 48 species included in this key, a list of which can be found in the fact sheet index.

Other scales key

This key has been built to accommodate pest scale insects in various families which were not treated in the soft scales (Coccidae) or mealybug (Pseudococcidae, Rhizoecidae and Putoidae) keys. Those species were selected because they were intercepted more than five times at U.S. ports-of-entry between 1995 and 2012, or are considered likely threats for introduction. A list of the families included is given below, with links to information about them. A list of the 47 species from these families included in this key can be found in the fact sheet index.

  • flat grass scales (Aclerdidae)
  • pit scales (Asterolecaniidae)
  • false armored scales (Conchaspididae)
  • cochineal scales (Dactylopiidae)
  • felt scales (Eriococcidae)
  • lac scales (Kerriidae)
  • false pit scales (Lecanodiaspididae)
  • pine bast scales (Matsucoccidae)
  • giant scales (Monophlebidae)
  • ensign scales (Ortheziidae)
  • stictococcids (Stictococcidae)