Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

FNZ 41 - Coccidae (Insecta: Hemiptera: Coccoidea) - Popular summary

Hodgson, CJ; Henderson, RC 2000. Coccidae (Insecta: Hemiptera: Coccoidea). Fauna of New Zealand 41, 264 pages.
( ISSN 0111-5383 (print), ; no. 41. ISBN 0-478-09335-7 (print) ). Published 23 Feb 2000

Popular summary

Soft scale insects

The soft scale family Coccidae is one of ten families of plant-sucking scale insects present in New Zealand. The 57 known species can be divided into two distinct groups: 43 indigenous species in 11 genera that are restricted to New Zealand, and 14 cosmopolitan (or adventive) species in six genera that are generally of world-wide distribution, and probably arrived here accidentally on imported plant material. Most of the indigenous species are quite closely related and are covered in a glassy wax cover characteristically divided into polygonally-shaped plates. No Māori names are known for any of these insects.

The native species of soft scales are associated with native trees and shrubs and there is only a single record of a native species found on any of the numerous introduced plant species. Many of these native scale species have quite wide host-ranges whilst others appear to be more host-specific. The closeness of the association between the indigenous species and the New Zealand flora, on which there are no definite records of serious damage, suggests that the association between the scale and its host plants has had a long evolutionary history. None of these native species are of economic importance, and none has been recorded outside New Zealand.

Most of the introduced or adventive species are of some economic importance, mainly on introduced crops and cultivated garden plants, both indoors and outdoors. Two species of wax scales require control on citrus, whilst other species are occasionally significant on plums, apricots, and cherries. Biological control agents were imported earlier to control two of the pest scales. One hymenopterous parasitoid species was introduced in 1921 to control brown soft scale (Coccus hesperidum Linnaeus), and four species have been imported against black scale (Saissetia oleae (Olivier)). Generally the cosmopolitan scales in New Zealand are each attacked by several species of parasitoids.

Like many other related sap-sucking insects, the soft scales eliminate honeydew from the anus. This is a sugary solution produced in the gut after feeding on the plant sap. A black sooty mould fungus often grows on the honeydew. In most parts of the world, this honeydew is attractive to ants, but in New Zealand only a single native species is known to be ant-attended -- the reasons for this are unknown. However, soft scales are rarely as abundant as some other honeydew-producing scale insect families, such as the margarodids and eriococcids, and so are not the main cause of the sooty moulds so abundant on beech, manuka, and kanuka.

The life cycle and appearance of male and female soft scales are quite different. The stages that are most often seen are those of the female, which passes through two or three immature stages before becoming sexually mature, despite still looking immature. The males, on the other hand, pass through four stages before giving rise to the very small, fly-like, adult male. Quite unlike the adult female, the adult male has no functional mouthparts and only lives for a few days. Its sole function is to locate and fertilise the female. Some species, which live under the bark of trees, are thought to have dispensed with males and to reproduce asexually. Most of the native species seem to have only one or two generations a year.

The main stage used to identify and describe a species of scale insect is the adult female and this revision deals only with this stage. Mature females rarely reach 10 mm long and many are only 3-4 mm when fully grown and, although many New Zealand species can be identified by the form of the glassy cover or test, it is best to check the identification with a microscope by mounting the specimen on a glass slide. The characters that are most critical for identification are the numerous minute wax-secreting pores found over most of the body, and these require a high-power microscope for examination.