INTERESTING INSECTS

By N A Martin (2019)

Gahnia glassy scale

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]

Unlike the circular shape of other scale insect in the genus, Kalasiris, Gahnia glassy scale insects relatively long and narrow, which is a better fit for the narrow Ghania leaves.

Gahnia glassy scale insects appear to have only one generation per year in Auckland. Male scales have been found in late winter with small female scales. Females with eggs are found in spring and early summer.

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 first instar nymphs of males and females are identical. The first instar nymphs, often called crawlers, are the main dispersal stage of Gahnia glassy scale. When it is fully grown, it moults, changes its skin, but keeps the test. The second instar nymph is also a feeding stage. Unlike many species of scale insects both the males and females have elongated tests.

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 in other species of scale insect grows to about 2-3 times that size. The final test is elongated, with rounded ends. It has a flat top made up of wax plates and a short vertical side wall that is fixed to the leaf. Around the upper edge of the test are projecting ‘triangular’ plates, longest at each end of the scale case. After mating the mature female forms a brood chamber at the rear end of the scale into which she lays eggs. Her body shrinks to the front of the test as the brood chamber fills with eggs.

The fully grown male test is similar to that of the female, but smaller and it has a rear hinged flap that allows the winged adult to emerge. When the male nymphs have finished feeding it may move to a new site where it secretes a wax base that firmly attaches it to the plant surface and creates a chamber. In the chamber 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.

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 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 tuft. 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 of Gahnia glassy scale, Kalasiris martini (Hemiptera: Coccidae), on the underside of a leaf of Gahnia, Gahnia sp. (Cyperaceae): note that the body has shrunk to the head end and the cavity is filled with eggs. Creator: Nicholas A. Martin. © Landcare Research. [Image: 3087]

Adult female of Gahnia glassy scale, Kalasiris martini (Hemiptera: Coccidae), on the underside of a leaf of Gahnia, Gahnia sp. (Cyperaceae): note vertical side under the horizontal wax projections. Creator: Nicholas A. Martin. © Landcare Research. [Image: 3088]

Head end of an adult female of Gahnia glassy scale, Kalasiris martini (Hemiptera: Coccidae), on the underside of a leaf of Gahnia, Gahnia sp. (Cyperaceae): note the shrunken body. Creator: Nicholas A. Martin. © Landcare Research. [Image: 3089]

Rear end of an adult female of Gahnia glassy scale, Kalasiris martini (Hemiptera: Coccidae), on the underside of a leaf of Gahnia, Gahnia sp. (Cyperaceae): note the white excretory orifice and the eggs in the cavity. Creator: Nicholas A. Martin. © Landcare Research. [Image: 308A]

An adult female of Gahnia glassy scale, Kalasiris martini (Hemiptera: Coccidae), on the underside of a leaf of Gahnia, Gahnia sp. (Cyperaceae): note the white excretory orifice and the eggs in the cavity. Creator: Tim Holmes. © Plant & Food Research. [Image: 307Y]

An empty male Gahnia glassy scale, Kalasiris martini (Hemiptera: Coccidae), on the underside of a leaf of Gahnia, Gahnia sp. (Cyperaceae): note the white hinge of the rear flap through which the adult male leaves the wax scale. Creator: Nicholas A. Martin. © Landcare Research. [Image: 308B]

The upturned scale cover of an adult female of Gahnia glassy scale, Kalasiris martini (Hemiptera: Coccidae), showing the thick side walls, shrunken body (left), egg shells.and a few eggs (left). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3083]

The upturned scale cover of an adult female of Gahnia glassy scale, Kalasiris martini (Hemiptera: Coccidae), showing the thick side walls and shrunken body (right). The egg shells.are still attached to the leaf. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3086]

An adult female of Gahnia glassy scale, Kalasiris martini (Hemiptera: Coccidae), on the underside of a leaf of Gahnia, Gahnia sp. (Cyperaceae): note the white excretory orifice and the eggs in the cavity. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 307Z]

First instar (stage) nymphs of Gahnia glassy scale, Kalasiris martini (Hemiptera: Coccidae), on the underside of a leaf of Gahnia, Gahnia sp. (Cyperaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3081]

The mature female Gahnia glassy scale are distinctive. The elongated wax test (case) is rounded at each end and made of distinct wax plates. There is a low vertical side wall, above which are projecting ‘triangular’ wax plates, longest at each end of the scale case.

Male scales are similar in appearance to those of the female. They have a distinct ‘hinge’ at the rear end to allow the winged adult male to emerge.

Adult female of Gahnia glassy scale, Kalasiris martini (Hemiptera: Coccidae), on the underside of a leaf of Gahnia, Gahnia sp. (Cyperaceae): note that the body has shrunk to the head end and the cavity is filled with eggs. Creator: Nicholas A. Martin. © Landcare Research. [Image: 3087]

An adult female of Gahnia glassy scale, Kalasiris martini (Hemiptera: Coccidae), on the underside of a leaf of Gahnia, Gahnia sp. (Cyperaceae): note the white excretory orifice and the eggs in the cavity. Creator: Tim Holmes. © Plant & Food Research. [Image: 307Y]

The empty scale covers of female and male Gahnia glassy scales, Kalasiris martini (Hemiptera: Coccidae), on the underside of a leaf of Gahnia, Gahnia sp. (Cyperaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3084]

Two empty scale covers of male Gahnia glassy scales, Kalasiris martini (Hemiptera: Coccidae), on the underside of a leaf of Gahnia, Gahnia sp. (Cyperaceae): note the white hinge of the rear flap through which the adult male leaves the wax scale. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3082]

An old scale cover of a female Gahnia glassy scales, Kalasiris martini (Hemiptera: Coccidae), on the underside of a leaf of Gahnia, Gahnia sp. (Cyperaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3085]

First instar (stage) nymphs of Gahnia glassy scale, Kalasiris martini (Hemiptera: Coccidae), on the underside of a leaf of Gahnia, Gahnia sp. (Cyperaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3080]

No natural enemies of Gahnia glassy scale are known.

Gahnia glassy scale insects live on the underside of leaves of Māpere, Gahnia setifolia (Cyperaceae) a plant that is found in light shade in native forests. The scale insect may also live on other Ghania species which are best identified when seeds are present.

Feeding and honeydew

Like other Hemiptera, Gahnia glassy 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 Gahnia glassy 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 plant of Māpere, Gahnia setifolia (Cyperaceae) growing in light forest. A host plant of Gahnia glassy scale, Kalasiris martini (Hemiptera: Coccidae). Creator: Nicholas A. Martin. © All rights reserved. [Image: 308C]

Adult female of Gahnia glassy scale, Kalasiris martini (Hemiptera: Coccidae), on the underside of a leaf of Gahnia, Gahnia sp. (Cyperaceae): note that the body has shrunk to the head end and the cavity is filled with eggs. Creator: Nicholas A. Martin. © Landcare Research. [Image: 3087]

The empty scale covers of female and male Gahnia glassy scales, Kalasiris martini (Hemiptera: Coccidae), on the underside of a leaf of Gahnia, Gahnia sp. (Cyperaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3084]

Two empty scale covers of male Gahnia glassy scales, Kalasiris martini (Hemiptera: Coccidae), on the underside of a leaf of Gahnia, Gahnia sp. (Cyperaceae): note the white hinge of the rear flap through which the adult male leaves the wax scale. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3082]

First instar (stage) nymphs of Gahnia glassy scale, Kalasiris martini (Hemiptera: Coccidae), on the underside of a leaf of Gahnia, Gahnia sp. (Cyperaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3080]

Hodgson CJ, Gunawardana DN, Richmond JE. 2016. A new species in the indigenous New Zealand soft scale insect genus Kalasiris Henderson & Hodgson (Hemiptera: Sternorrhyncha: Coccomorpha: Coccidae) on Gahnia setifolia (Cyperaceae). Zootaxa. 4092 (1): 122-128.

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.