Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

FNZ 21 - Margarodidae (Insecta: Hemiptera) - Popular summary

Morales, CF 1991. Margarodidae (Insecta: Hemiptera). Fauna of New Zealand 21, 124 pages.
( ISSN 0111-5383 (print), ; no. 21. ISBN 0-477-02605-9 (print), ). Published 27 May 1991

Popular summary

The Margarodidae are one of eleven families in New Zealand of the plant-sucking scale insects. Two subfamilies are represented, one by the introduced cottony cushion scale (and, in quarantine only, the Seychelles scale), and the other, the giant scales, by ten native species. These latter are all test-formers, that is, they secrete a protective external coating which varies in texture and appearance from species to species. No Māori names are known for any of these insects.

The cottony cushion scale, which is believed to have originated in Australia, was for a time a serious pest in citrus orchards and gardens. It was brought under control by introducing one of its natural predators, a species of ladybird beetle, and is now a relatively uncommon pest in New Zealand.

The native species of Margarodidae in New Zealand are associated with native trees and shrubs. Most of them are host-specific, and have a long history of evolution in association with their particular host plants. They play a significant role in forest ecology: the sugary secretion produced by the feeding stages is at times sufficiently abundant to provide nourishment for the bacteria and fungi that break down forest-floor litter, for bees, wasps, and other insects, and even for birds. The honeydew produced by one species associated with the trunks of southern beech trees is harvested by foraging bees to make 'forest honey', which has considerable export value.

A sooty mould coating the trunks of host trees such as beech, manuka, and kanuka is often the most obvious indication of the presence of margarodid scales. On closer inspection long, thread-like extrusions - one from the test of each immature scale, and with a droplet of honeydew on the end - are also distinctive. Another conspicuous sign of giant scales are the clusters of white cocoons of the male pupae of some species.

The adult males are usually fully winged, dark red, rather fly-like insects lacking mouthparts, and hence short-lived and not easy to find. Their principal purpose in life is to find and mate with the wingless females, which look like large, pink lozenges with legs and may be found crawling on the forest floor or on the bark of trees during summer. Some margarodids have no known male stage.

The life history of margarodid scales is marked by rather dramatic changes in appearance undergone between the various stages, in both sexes. Some of the life stages are very simple in body structure, and offer few readily visible clues to their identity. The study of these scales consequently requires examination of microscope slides.

Differences in the appearance and disposition of minute structures such as pores and hairs may be critical in determining identity from morphology, and this is a task for the specialist. As our understanding of margarodid classification improves, however, some reliance may be placed on biological indicators of identity that can be used by the non-specialist, such as the host plant - or the site on the host plant - from which a specimen was collected.

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