Kanuku orange scale - Asterolecanium vitreum

By N A Martin (2019)

Caption:

Classification

Phylum

Arthropoda

Class

Insecta

Order

Hemiptera

Superfamily

Coccoidea

Family

Asterolecaniidae

Scientific name

Asterolecanium vitreum Russell, 1941

Common names

Kanuku orange scale

Biostatus and distribution

The distinctive endemic Kanuku orange scale insects live on the upper side of leaves of Kanuka. It has been found from Lake Wanaka in the South Island up to the Three Kings Islands. Since the collections were made, the host plant Genus, Kunzea (Myrtaceae) has been revised. Because of its extensive geographic distribution, Kanuku orange scale insects are likely to live on several or even all the Kunzea species in New Zealand.

Conservation status: Uncommon, widespread on its host trees, not endangered.

Life stages and annual cycle

Lifecycle of a soft scale, Coccidae (Hemiptera). The male propupae and pupa live under the male second instar cover. In this example there are three nymphal stages before the adult female. Creator: Nicholas A. Martin. © Diagram adapted from Figure 2 in Hodgson C.J. and Henderson R.C. 2000. Fauna of New Zealand. 41. [Image: 2MT3]

The Kanuku orange scale insect may have one generation per year associated with the production of new leaves by its host plant. The insects live on leaves of Kanuka, Kunzea species. In her 1941 description of the species, Louise May Russell states that the insect lives on both sides of the leaf. I have only seen them on the upper surface the upper side of leaves of Kanuka.

The cover of the adult female is ovoid and convex and has a small pale posterior projection. It is orange and has whitish marginal filaments. A characteristic of scale insects in this genus is that the margin of the body has 8-shaped pores that can be seen in microscope slide preparations. After fertilization, the female lays eggs under the scale cover. She may only lay a few eggs at a time or if she lays a lot of eggs at one time her body must shrink to make room for the eggs.

After the first instar nymphs, crawlers, hatch from their eggs, they leave the female scale cover. They are elongate-ovoid in shape and have three pairs of legs and a pair of antennae. They and walk to young leaves on the same or another branch and start to feed. The first instar nymph crawls to where the adult female or adult male will develop. When they have reached full size, they moult into the next nymphal stage. There may be two or three female nymphal stages. The last nymphal stage has no functional legs. After moulting it probably looks like a small adult female. When fully grown it moults into the adult female.

There are no reports about the male scale and adult males. The male scale of an unnamed species in the same genus, is elongated with parallel lateral sides. It is covered with fine ‘bristles’. When the second stage nymphal instar is fully grown, it probably moults within the scale cover into a non-feeding propupa. This in turn moults into a pupa that has wing buds. It is presumed that the pupa moults into an adult winged male that also has functional legs. In many other scale insects, the males can mate with females in their own colony, but can also go to females in other colonies.

Feeding

Adult females and the nymphs have sucking mouthparts. Specially shaped long rods called stylets are used for feeding. Until used for feeding, the tips of the stylets held in the short sheath-like rostrum. When it wishes to feed, the scale insect moves the tip of the rostrum onto the surface of the plant. The stylets are then gradually pushed into the plant. The stylets form two tubes, one down which saliva is pumped into plant cells and the second tube through which it sucks the contents of the plant cells. The insect inserts its stylets into the phloem, the plant vessels for transmitting sap from the leaves to other parts of the plant. The sap has a high volume of water and sugars, more than the insect needs. It excretes the excess water and sugar, which is called honeydew.

Walking, flying and dispersal

The first instar nymphs have legs and can walk. They are often called crawlers. All the other nymphal stages and adult females have no functional legs. The first instar nymph is the main stage for dispersal. Most crawlers walk to a place on a twig or another branch. Some crawlers disperse to other trees; most long distance dispersal is by air. It is not known if crawlers of this species go to high points of the plant and stand up to catch the wind. Adult males have legs and wings. They can walk over a stem in search of females with which to mate. They can also fly to nearby colonies, and may be carried further by wind.

Kanuku orange scale, Asterolecanium vitreum (Hemiptera: Asterolecaniidae) on a leaf of Kanuka, Kunzea ericoides s.l. (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 31WT]

Drawings of microscope preparations of Kanuku orange scale, Asterolecanium vitreum (Hemiptera: Asterolecaniidae) showing the 8-shaped pores. Creator: Luise May Russell. © Drawings published in Miscellaneous Publications. US Department of Agriculture. 424: 1-324, Fig 81. [Image: 31WX]

Photograph of a microscope slide preparation of the hind end of a female Kanuku orange scale, Asterolecanium vitreum (Hemiptera: Asterolecaniidae): note the 8-shaped pores along the margin. Creator: Nicholas A. Martin. © Landcare Research. [Image: 31WV]

Photograph of a microscope slide preparation showing the 8-shaped pores on the margin the body of a female Kanuku orange scale, Asterolecanium vitreum (Hemiptera: Asterolecaniidae). Creator: Nicholas A. Martin. © Landcare Research. [Image: 31WW]

Kanuku orange scale, Asterolecanium vitreum (Hemiptera: Asterolecaniidae) on leaves of Kanuka, Kunzea ericoides s.l. (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 31WR]

Recognition

Kanuku orange scale insects are the only orange coloured dome shaped scale insect known to inhabit the upper side of leaves of Kanuka, Kunzea species (Myrtaceae).

Natural enemies

No natural enemies of the Kanuku orange scale are known. It may be eaten by predatory insects and birds.

Host plants

Since collections of Kanuku orange scale were made, its host plant Genus, Kunzea (Myrtaceae) has been revised. Because of its extensive geographic distribution, Kanuku orange scale insects are likely to live on several or even all the Kunzea species in New Zealand.

Feeding and honeydew

Like other Hemiptera, Kanuku orange scale insects have sucking mouth parts. The long stylets, special shaped rods, are held in a short rostrum on the underside of the body. When the insect wishes to feed the stylets are then gradually pushed into the plant. The inner pair of stylets, form two tubes, one through which saliva is injected into the plant and a second through which plants juices are sucked up into the insect. The Kanuku orange scale inserts its stylets into the phloem, the plant vessels for transmitting sap from the leaves to other parts of the plant. The sap has a high volume of water and sugars, more than the insect needs. It excretes the excess water and sugar, which is called honeydew.

Table: Host plants of the Kanuku orange scale, *Asterolecanium vitreum* (Hemiptera: Asterolecaniidae) from Plant-SyNZ database (28 May 2019). The reliability score shows the quality of evidence for the host association (1-10, 10=high).
Common Name(s)	Scientific Name	Family	Reliability Index	Biostatus
White tea tree, Kānuka, Kōpuka, Manuea, Mānuka, Mānuka-rauriki, Mārū, Rauiri, Rauwiri	Kunzea ericoides s.l. (A.Rich.) Joy Thomps.	Myrtaceae	10	indigenous, non-endemic

Information sources

Russel, L.M. 1941. A classification of the scale insect genus Asterolecanium. Miscellaneous Publications. US Department of Agriculture. 424:1-324.

Plant-SyNZ: Invertebrate herbivore-host plant association database. plant-synz.landcareresearch.co.nz/

Acknowledgements

The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs.

Landcare Research New Zealand Limited (Landcare Research) for permission to use photographs.

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