Plumichiton nikau Henderson & Hodgson, 2000
Glassy nīkau scale
Biostatus and distribution
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.
Life stages and annual cycle
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.
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.
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.
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.
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.
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.
|Scientific Name||Common Name||Classification||Enemy Type||Reliability Index||Biostatus|
|Hypocrella duplex Petch||Orange puffs||Fungi: Ascomycota: Sordariomycetes: Hypocreales: Clavicipitaceae||pathogen||10||indigenous, non-endemic|
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.
|Common Name(s)||Scientific Name||Family||Reliability Index||Biostatus|
|Feather duster palm, Nikau palm, Nīkau||Rhopalostylis sapida H.Wendl. & Drude||Palmae||10||endemic|
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.