INTERESTING INSECTS

By N A Martin (2019)

Pōhutukawa button scale

The endemic Pōhutukawa button scale insects live on leaves and stems Pohutukawa, Metrosideros excelsa and Northern rata, Metrosideros robusta (Myrtaceae). The adult female scale induces a stem gall on which it lives. Most commonly found on the east coast of the North Island.

Conservation status: Not endangered, probably present where ever its host plants live.

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 Pōhutukawa button scale may have more than one generation per year. The main generation is in early summer. Nymphs are found on the underside of leaves alongside the midrib. Young females move to young green stems. Feeding by the females induces the stems to swell, forming galls.

Young adult females are light brown and covered in thin wax plates that makes them look hairy. Fully grown old female are dark brown and shiny. The body is almost round, but with a distinct anal cleft posteriorly and with an opening into brood chamber beneath abdomen. The dorsal surface rather flat. The distinctive feature is a central true dorsum with indistinct radial ridges that is only about l/5th total width and about 1/3 total length. Lateral areas of dorsal surface are formed from an extension of the ventral surface (venter).

First instar nymph, crawlers, hatch from eggs in the female brood chamber. They walk to the undersides of leaves. Here they feed and grow, more than doubling in size. They are the only life stage with functional legs. They have three pairs and a pair of antennae. The fully grown first instar nymph crawls to where the adult female or adult male will develop. The male stays on the underside of a leaf, while the female crawls onto a young stem where she moults into the second instar. The second instar female is a little large that the previous stage, while the young adult female is about the same size as the second instar nymph. Feeding by the adult female stimulates the stem to swell and form the gall. The female grows through the expansion of the ventral plate that spreads outwards and upwards so that it forms the bulk of the scale cover. Under the scale cover part of the scale body shrinks upwards to form a brood chamber in which the eggs are laid. The brood chamber connects to the outside by a ‘tunnel-like’ opening beneath the anal plates and between the anal lobes.

When the male second instar nymph has grown to full size, it moults into a propupa, the first of two none feeding stages. The propupa has short wing buds and the pupa has longer wing buds. These two stages develop in the chamber under the scale cover grown by the second instar male nymph. This scale cover is like those of males of other species in the family Coccidae. A special feature is that at the rear end is a hinged flap that the adult male can push open. When the adult male has fully formed, the pupal skin is shed. The male has one pair of wings and emerges backwards from beneath the test by means of the upwardly flexing plate on the posterior end of the test. It is a non-feeding stage and only lives for a few days while it finds and mates with a female.

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 legs. The first instar nymph is the main stage for dispersal. Most crawlers walk to a place on the leaf or another leaf on the stem. Some crawlers disperse to other plants; 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.

An old female Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) in a depression in the gall induced in a stem of Pohutukawa, Metrosideros excelsa (Myrtaceae): note splits in the bark over the gall. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AM]

Scanning electron micrograph of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) showing the true dorsum surrounded by part of the venter on the dorsal surface. © Figure M9 from Hodgson C.J. and Henderson R.C. 2000. Fauna of New Zealand. 41. [Image: 30AA]

A growing adult female Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) in a depression in the gall induced in a young stem of Pohutukawa, Metrosideros excelsa (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AG]

An upturned adult female Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) exposing the brood chamber with eggs. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AD]

Drawings of the female nymphs and adult of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae): note the large increase in size of the first instar, and that the second instar and adult female have no functional legs and the increase in size of the adult is from growth of the dorsal venter. © Modified from Figure 121 in Hodgson C.J. and Henderson R.C. 2000. Fauna of New Zealand. 41. [Image: 30A8]

Drawings of the male nymphs of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae): note the large increase in size of the first instar and that the second instar has no functional legs. © Modified from Figure 121 in Hodgson C.J. and Henderson R.C. 2000. Fauna of New Zealand. 41. [Image: 30A9]

First instar (stage) nymphs of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) by the midrib on the underside of a young leaf of Pohutukawa, Metrosideros excelsa (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AN]

First and second instar (stage) nymphs of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) on the underside of a leaf of Pohutukawa, Metrosideros excelsa (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AV]

First and second instar (stage) nymphs of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) on the underside of a leaf of Pohutukawa, Metrosideros excelsa (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AW]

Second instar (stage) nymphs and young adults of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) on a young stem of Pohutukawa, Metrosideros excelsa (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AK]

Two young adults of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) on a young stem of Pohutukawa, Metrosideros excelsa (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AL]

Two adults of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) on a young stem of Pohutukawa, Metrosideros excelsa (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AB]

A young (right) and mature (left) first instar male nymphs of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) on the upper side of a leaf of Pohutukawa, Metrosideros excelsa (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AH]

A male nymph of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) on the underside of a leaf of Pohutukawa, Metrosideros excelsa (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AJ]

A male second instar (stage) of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) on the underside of a leaf of Pohutukawa, Metrosideros excelsa (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AI]

Empty male second instar (stage) scale covers of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) on the underside of a leaf of Pohutukawa, Metrosideros excelsa (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AU]

A dead adult male of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AQ]

Two images of the underside of an adult male of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae): note the pair of wings and the pair of white wax ‘tails’. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AP]

The presence of Pōhutukawa button scale on its two host plants, Pohutukawa, Metrosideros excelsa and Northern rata, Metrosideros robusta (Myrtaceae) can usually be recognised by the presence of the distinctive stem galls. However, there is a need to check that the galls were not induced by the Pohutukawa stem-gall wasp (see below). Also some trees may develop gall like swellings at leaf nodes.

The brown, circular adult female scale is usually found in a depression in a stem galls. The young female nymphs may be on the stems or underside of leaves. The first and second instar males are seen on the underside of leaves where they are mainly by the mid rib. The empty male scale covers (teste) are transparent and have a hinged flap at one end.

On Pohutukawa, Metrosideros excelsa (Myrtaceae), stem galls induced by Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) can be recognized by the presence of tiny exit holes in galls. Young galls without exit holes (because larvae and pupae are still developing and no adults have emerged) could be mistaken for similar looking stem galls that are induced by Pōhutukawa button scale insects. Dissection of the gall is required if identification of the gall is needed. Galls made by gall wasps contain cells for the larvae and pupae.

Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) in a depression in the gall induced in a stem of Pohutukawa, Metrosideros excelsa (Myrtaceae): note splits in the bark over the gall. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 308F]

Side view of a Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) in a depression in the gall induced in a young stem of Pohutukawa, Metrosideros excelsa (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AF]

A young stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with galls induced by the Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae): note splits in the bark over the gall. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 308D]

An old stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with galls induced by the Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae): note splits in the bark over the gall. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 308E]

First and second instar (stage) nymphs of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) on the underside of a leaf of Pohutukawa, Metrosideros excelsa (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AV]

First and second instar (stage) nymphs of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) on the underside of a leaf of Pohutukawa, Metrosideros excelsa (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AW]

Empty male second instar (stage) scale covers of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) on the underside of a leaf of Pohutukawa, Metrosideros excelsa (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AU]

Empty scale cover (teste) of a male second instar (stage) (right) of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) and a nymph or male of a Felted scale insect (Hemiptera: Eriococcidae) (left) on the underside of a leaf of Pohutukawa, Metrosideros excelsa (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AR]

A stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the exit holes made by adult wasps. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 308I]

A old stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the three exit holes made by adult wasps. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 308J]

A stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) that has been cut to expose the cells in which the larvae live. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 308H]

An old woody stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) that has been cut to expose the old cells in which the larvae lived. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 308L]

The only natural enemies of Pōhutukawa button scale known are unknown species of parasitic wasps (Hymenoptera). The female wasp lays an egg in a scale. The wasp larva lives in the scale insect until the larva is fully grown. It then pupates within the scale cover (teste). The adult emerges from the pupa and when its wings and body have hardened, it chews a hole in the scale teste through which it emerges. Wasp parasitoids attack and breed in both the smaller male and larger female scale insects. There can be more than one larvae in some female scales.

An upturned adult female Pōhutukawa button scale, Lecanochiton actites (Hemitpera: Coccidae) with a larva of a parasitic wasp (Hymenoptera). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AE]

Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) in a depression in the gall induced in a stem of Pohutukawa, Metrosideros excelsa (Myrtaceae): note splits in the bark over the gall and the wasp exit hole in the scale. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 308G]

Adult female Pōhutukawa button scale, Lecanochiton actites (Hemitpera: Coccidae) in a depression in the gall induced in a stem of Pohutukawa, Metrosideros excelsa (Myrtaceae): note the round exit hole made by a parasitic wasp (Hymenoptera). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30B1]

Adult female Pōhutukawa button scale, Lecanochiton actites (Hemitpera: Coccidae) in a depression in the gall induced in a stem of Pohutukawa, Metrosideros excelsa (Myrtaceae): note the two round exit holes made by parasitic wasps (Hymenoptera). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AZ]

A male Pōhutukawa button scale, Lecanochiton actites (Hemitpera: Coccidae) on a leaf of Pohutukawa, Metrosideros excelsa (Myrtaceae): note the round exit hole made by a parasitic wasp (Hymenoptera). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30B0]

Pōhutukawa button scale insects live on leaves and stems Pohutukawa, Metrosideros excelsaand Northern rata, Metrosideros robusta (Myrtaceae). The adult female scale induces a stem gall on which it lives.

Feeding and honeydew

Like other Hemiptera, Pōhutukawa button 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 Pōhutukawa button 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.

A young stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with galls induced by the Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae): note splits in the bark over the gall. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 308D]

A stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with galls induced by the Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae): note female scale insects in the depressions on the galls. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AC]

Empty male second instar (stage) scale covers of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) on the underside of a leaf of Pohutukawa, Metrosideros excelsa (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AT]

Empty male second instar (stage) scale covers of Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) on the underside of a leaf of Pohutukawa, Metrosideros excelsa (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30AS]

Hodgson CJ, Henderson RC. 2000. Coccidae (Insecta: Hemiptera: Coccoidea). Fauna of New Zealand. 41: 1-264.

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

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