INTERESTING INSECTS

By N A Martin (2019)

Glassy nīkau scale

This distinctive endemic scale insect is found on leaves of Nikau palm, Rhopalostylis sapida (Palmae). It lives in lowland forests and in the North Island and northern South Island where the Nikau palm grows.

Conservation status: Not endangered, found on Nikau palms in native forest.

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 annual cycle of the Glassy nīkau scale is not known. There may be more than one generation per year. Adult males and females producing nymphs have been found in January.

The bodies of adult females and female and male nymphs are covered by a test, glassy wax plates, secreted by the upper surface of the insect’s body. On the underside of the body are three pairs of legs and a pair of antennae. There is also a short rostrum which houses the stylets that are used for feeding. When a nymph is fully grown it moults, shedding its old skin, but it stays beneath its test. It may walk to a new site where it settles down to feed, grow and enlarge the test.

The adult female scale covers the leaf surface with a gum-like wax that sticks the test to the leaf. Its colour varies from light green and light brown. The wax scale cover is convex and oval. It has thick plates that are fused into 3 longitudinal rows down the centre. It also has raised sides that are formed from a submarginal row of plates that are fused together. When mature the adult female retracts her abdomen to form a brood chamber. The newly hatched nymphs are found in the brood chamber before emerging from beneath the hind end of the female.

The first instar nymphs of males and females are identical. The first instar nymphs, often called crawlers, are the main dispersal stage of Glassy nīkau scale. When it is fully grown, it moults, changes its skin, but keeping the test. The second instar nymph is also a feeding stage. The males and females can be distinguished at this stage. The male nymphs develop a more elongate, glassy test. When the male has finished feeding it may move to a new site where it secretes a wax base that firmly attaches it to the plant surface. Under the test the male nymph moults into a propupa, a non-feeding stage with short wing buds. Later the propupa moults into a pupa which has larger wing buds. When the adult male has fully formed, the pupal skin is shed. It has one pair of wings and emerges backwards from beneath the test, wingtips first, 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.

Females have three nymphal instars (stages). They all feed and the only difference between them is size. The young adult female is the size of the fully grown third instar nymph and grows to about 2-3 times that size. The young adult is rather flat and round with a glossy test of wax plates. It develops a side wall as it matures. The body of the young female is light green but gradually becomes dark grey. It can be seen through the glassy wax plates. Each wax plate is composed of layers of wax, uppermost layer is the smallest (secreted when insect was small); most basal layers of each plate are the broadest, filling plate area (and secreted most recently). The mature female has a brood chamber into which eggs are laid and in which the nymphs hatch before leaving.

Feeding

Adult females and juvenile scales 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 nymphs and adult females retain legs and can walk, though the adult female and the second and third instar (stage) nymphs are much less likely to walk than the first instar which is commonly called a crawler. It is the main stage for dispersal. Most crawlers walk to a place on the leaf or another leaf on the stem or branch. 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 leaf in search of females with which to mate. They can also fly to nearby colonies, and may be carried further by wind.

Adult female Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae), on a leaf of a Nikau palm, Rhopalostylis sapida (Palmae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3107]

Adult female Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae): note the excretory opening (left) and layers of wax making up each wax plate. Creator: Nicholas A. Martin. © Landcare Research. [Image: 310I]

First instar (stage) nymphs and the underside of an adult female Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae): note transparent layer on the underside showing the brood chamber with eggs and newly hatched nymphs. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 310C]

First instar (stage) nymphs and the underside of an adult female Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae): note the thin wax area (left) that glued the female scale to the leaf. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 310D]

Three nymphs of Glassy nīkau scales, Plumichiton nikau (Hemiptera: Coccidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3105]

Two nymphs of Glassy nīkau scales, Plumichiton nikau (Hemiptera: Coccidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 310A]

Young male second instar (stage) nymph of Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3102]

Fully grown male second instar (stage) nymph of Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3109]

A young nymph and a fully grown male second instar (stage) nymph of Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3101]

Second instar male wax cover of a Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae): note the hinged opening (left) through which the adult male leaves. Creator: Nicholas A. Martin. © Landcare Research. [Image: 310K]

Second instar male wax cover of a Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae): note the hinged opening (left) through which the adult male leaves and the vertical side walls. Creator: Nicholas A. Martin. © Landcare Research. [Image: 310L]

An adult male of Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae) exposed in its wax scale cover Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3108]

Three views of an adult male of Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 310E]

Glassy nīkau scale are only found on leaves of Nikau palms. The adult female scales are distinctive. The

glassy wax scale cover is convex and oval, with thick plates that are fused into 3 longitudinal rows down the centre. It also has raised sides that are formed from a submarginal row of plates that are joined together. The colour of the scale varies from light green and light brown.

Male scales are similar in appearance to those of other species of soft scale insects (Coccidae) and are found on Nikau palm leaves.

Adult female Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae), on a leaf of a Nikau palm, Rhopalostylis sapida (Palmae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30ZZ]

Nymphs and an adult female Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae), on a leaf of a Nikau palm, Rhopalostylis sapida (Palmae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3106]

Adult female Glassy nīkau scales, Plumichiton nikau (Hemiptera: Coccidae), on a leaf of a Nikau palm, Rhopalostylis sapida (Palmae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 310G]

Male and adult female Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae), on a leaf of a Nikau palm, Rhopalostylis sapida (Palmae): note in the male scale, the round exit holes made by adult parasitic wasps. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 310H]

Nymphs and a male Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae), on a leaf of a Nikau palm, Rhopalostylis sapida (Palmae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 310B]

Adult female Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae), on a leaf of a Nikau palm, Rhopalostylis sapida (Palmae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 310M]

Two natural enemies have been found associated with Glassy nīkau scale, a fungal pathogen and a wasp parasitoid. It is likely that several insects are predators of this scale insect.

Pathogen

The fungal pathogen, Orange puffs, is flamboyant and decorative on leaves of Nikau palms. The examples photographed were found in August. It has been found on three other species of soft scale, Coccidae.

Parasitoids

At least one species of wasp parasitoid has been reared from Glassy nīkau scale insects. They have only been found associated with male scales. The female parasitoids lay an egg in a scale insect. The larva lives in or on the body of the scale insect. When the with wasp larva is fully grown it kills the scale insect and pupates under the scale cover. The adult wasp chews a hole in the scale cover though which it emerged.

Orange puffs fungus, Hypocrella duplex (Ascomycota: Clavicipitaceae) infecting nymphs of Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae), on a leaf of a Nikau palm, Rhopalostylis sapida (Palmae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30ZW]

Orange puffs fungus, Hypocrella duplex (Ascomycota: Clavicipitaceae) infecting nymphs of Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae), on a leaf of a Nikau palm, Rhopalostylis sapida (Palmae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30ZX]

Orange puffs fungus, Hypocrella duplex (Ascomycota: Clavicipitaceae) infecting a nymph of Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae). Creator: Nicholas A. Martin. © Landcare Research. [Image: 310J]

Two scales of male Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae), on a leaf of a Nikau palm, Rhopalostylis sapida (Palmae): note one scale has an exit hole made by an adult parasitic wasp (Hymenoptera). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30ZY]

Pale pupae of a parasitic wasp (Hymenoptera) dissected from scales of male Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae), on a leaf of a Nikau palm, Rhopalostylis sapida (Palmae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3103]

Dark pupae of a parasitic wasp (Hymenoptera) dissected from scales of male Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae), on a leaf of a Nikau palm, Rhopalostylis sapida (Palmae): note one scale has an exit hole made by an adult parasitic wasp (Hymenoptera). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3100]

The upper side (left) and underside (right of an adult a parasitic wasp (Hymenoptera) that emerged from a scale of male Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3104]

The Glassy nīkau scale only lives on the leaves of Nikau palms. It may be found on the upper and lower surface of the leaf.

Feeding and honeydew

Like other Hemiptera, Glassy nīkau 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 Glassy nīkau 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.

Adult female Glassy nīkau scales, Plumichiton nikau (Hemiptera: Coccidae), on a leaf of a Nikau palm, Rhopalostylis sapida (Palmae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 310G]

Male and adult female Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae), on a leaf of a Nikau palm, Rhopalostylis sapida (Palmae): note in the male scale, the round exit holes made by adult parasitic wasps. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 310H]

Two images of male Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae), on a leaf of a Nikau palm, Rhopalostylis sapida (Palmae): note the side wall visible in the right image. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 310F]

Nymphs and a male Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae), on a leaf of a Nikau palm, Rhopalostylis sapida (Palmae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 310B]

Nymphs and an adult female Glassy nīkau scale, Plumichiton nikau (Hemiptera: Coccidae), on a leaf of a Nikau palm, Rhopalostylis sapida (Palmae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3106]

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.

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