INTERESTING INSECTS

By N A Martin (2018)

Soft wax scale

Gascardia destructor (Newstead, 1917)

This adventive scale insect was first reported to be in New Zealand in 1940. It is found in the Northern half of New Zealand. It is mainly found on cultivated plants and is an important pest of citrus in Gisborne and Northland.

Conservation status: The Soft wax scale is pest of Citrus trees.

Adult females are coated with a thick, white, soft wax that is ‘wet’ to the touch. They are strongly convex and irregularly in shape. They are between 3.0-5.5 mm long and 1.5-3.0 mm wide. On the underside of the scale are a pair of tiny antennae and three pairs of tiny legs. It also has a short rostrum that holds the tips of the stylets that are inserted into the plant for feeding. At the rear end. there is hole through which excess liquid (honeydew) is excreted. Old females may become grey-white with sooty mould fungus.

When fully grown, the female lays eggs into a brood chamber under her body which gradually shrinks as it is converted into eggs. After hatching from the egg the nymph which has antennae and three pairs of legs, leaves the brood chamber through the anal orifice. The first instar (stage) nymph, which is called a crawler, walks to the upper surface of a leaf and settles by a vein. It inserts its stylets into the plant to feed. The body of the oval shaped scale is red and grows patches of white wax on top and laterally. When the first instar nymph is fully grown it moults into the next nymphal stage. The second instar nymph is similar to the first instar, but larger. It is also usually found on plant leaves. The third, and last nymphal stage usually crawls to a stem before settling and feeding. The third instar is covered with a thick layer of white wax that extends forward like a horn. Round the base are small ‘holes’ in the white wax and two or more lines of ‘dry’ white wax.

In New Zealand, only females are known and there is only one generation per year. The adult females lay eggs in the summer. They hatch from January onwards. The species over-winters mainly as third instar nymphs and young adults. The old wax cases of adults can be seen all year.

Feeding

Nymphs and adult females of Soft wax scale 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. If 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 and dispersal

The nymphs and adult females have legs large enough for walking. All these stages can walk around the leaves and stems of the plant on which they are born. The main stage that spreads to new host plants is probably the first instar (stage) nymph. In other insects this stage can be disperse long distances 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 female Soft wax scale, Ceroplastes destructor (Hemiptera: Coccidae) on stem of Syzygium sp. (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T8J]

Some of the soft white wax removed from an adult female Soft wax scale, Ceroplastes destructor (Hemiptera: Coccidae) on stem of Syzygium sp. (Myrtaceae): note the dark red-brown rigid test that covers the scale body. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T83]

The underside of a female Soft wax scale, Ceroplastes destructor (Hemiptera: Coccidae): note the thin white wax base to the egg chamber and the groove through which honeydew was excreted. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T8H]

The pink eggs exposed in female Soft wax scale, Ceroplastes destructor (Hemiptera: Coccidae) on stem of Syzygium sp. (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T8E]

Two images of an upturned adult female Soft wax scale, Ceroplastes destructor (Hemiptera: Coccidae) showing the eggs, white egg shells and nymphs. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T81]

Pink eggs, white egg shells and first instar nymphs exposed in female Soft wax scale, Ceroplastes destructor (Hemiptera: Coccidae) on stem of Syzygium sp. (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T8G]

Pink eggs, white egg shells and first instar nymphs exposed in female Soft wax scale, Ceroplastes destructor (Hemiptera: Coccidae) on stem of Syzygium sp. (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T8F]

Small nymphs of Soft wax scales, Ceroplastes destructor (Hemiptera: Coccidae) on a leaf of Syzygium sp. (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T7X]

Small nymphs of Soft wax scales, Ceroplastes destructor (Hemiptera: Coccidae) on a leaf of Syzygium sp. (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T80]

Small nymphs of Soft wax scales, Ceroplastes destructor (Hemiptera: Coccidae) on a leaf of Syzygium sp. (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T7Z]

Third instar (stage) nymphs of Soft wax scale, Ceroplastes destructor (Hemiptera: Coccidae) on stems of Tahiti lime, Citrus aurantiifolia (Rutaceae): note the forward pointing ‘horn’ of white wax. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T88]

Third instar (stage) nymphs of Soft wax scale, Ceroplastes destructor (Hemiptera: Coccidae) on stems of Tahiti lime, Citrus aurantiifolia (Rutaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T89]

Third instar (stage) nymphs of Soft wax scale, Ceroplastes destructor (Hemiptera: Coccidae) on stems of Tahiti lime, Citrus aurantiifolia (Rutaceae): note the forward pointing ‘horn’ of white wax. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T8A]

Scale insects in the family Coccidae require specialist skills for their identification, but the adult females of the three species of Ceroplastes in New Zealand can be recognised by their thick covering of wax. They are mainly found on plant stems. The young nymphs of these scale insects are also distinctive. They are usually found on the upper side of leaves and have small white wax plates in a star-like rosette.

The adult female Soft wax scale, is covered by a thick, white, soft wax that is `wet' to touch. It has a strongly convex and irregular in shape. The young nymphs of these scale insects on the upper side of leaves have small white wax plates in a star-like rosette with short ‘arms’.

The Chinese wax scale, (Ceroplastes sinensis Del, Guercio, 1900) is the most distinctive of the three species. The mature females are coated with thick layer of off-white wax that is coloured pinkish brown in patches, and has white `dry' wax in lateral and dorsal depressions. The young nymphs of these scale insects on the upper side of leaves have small white wax plates in a star-like rosette. It is found in the same parts of New Zealand.

The Indian wax scale, (Ceroplastes ceriferus (Fabricius, 1798)) has only been found in Gisborne on Citrus trees. The Indian wax scale is coated with thick pinkish white ‘wet’ wax. It normally has an anteriorly projecting ‘horn’. It has white `dry' wax in lateral depressions. Plates are visible on older adult females.

Adult female Soft wax scale, Ceroplastes destructor (Hemiptera: Coccidae) on stem of Syzygium sp. (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T8I]

Adult female Soft wax scales, Ceroplastes destructor (Hemiptera: Coccidae) on stem of Syzygium sp. (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T84]

Small nymphs of Soft wax scales, Ceroplastes destructor (Hemiptera: Coccidae) on a leaf of Syzygium sp. (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T80]

Small nymphs of Soft wax scales, Ceroplastes destructor (Hemiptera: Coccidae) on a leaf of Syzygium sp. (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T7Z]

Third instar (stage) nymphs of Soft wax scale, Ceroplastes destructor (Hemiptera: Coccidae) on stems of Tahiti lime, Citrus aurantiifolia (Rutaceae): note the forward pointing ‘horn’ of white wax. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T88]

Adult female Chinese wax scale, Ceroplastes sinensis (Hemiptera: Coccidae) on stem of Syzygium sp., (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T9M]

Adult females of Chinese wax scale, Ceroplastes sinensis (Hemiptera: Coccidae) on the petiole of a leaf of Brazilian pepper tree, Schinus terebinthifolius (Anacardiaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T9F]

Adult females and third instar (stage) nymphs of Chinese wax scale, Ceroplastes sinensis (Hemiptera: Coccidae) on a stem of Mangrove, Avicennia marina (Acanthaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T8W]

Adult females and young nymphs of Chinese wax scale, Ceroplastes sinensis (Hemiptera: Coccidae) on a leaf of Brazilian pepper tree, Schinus terebinthifolius (Anacardiaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T9E]

No pathogens of Soft wax scale are known in New Zealand.

Parasitoids

In New Zealand only one wasp parasitoid has been reared from Soft wax scale. It is a hyperparasite, a parasite of other parasites.

Predators

Two of the three predators of Soft wax scale in New Zealand are ladybirds both of which come from other countries. The third predator is an unidentified species of tiny mite that normally feed on fungi associated with decaying plants. Mites were found feeding on scale insect eggs.

Adult female Soft wax scale, Ceroplastes destructor (Hemiptera: Coccidae) on stem of Syzygium sp., (Myrtaceae) with the exit hole of a wasp (Hymenoptera) parasitoid. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T82]

Underside of an adult female Soft wax scale, Ceroplastes destructor (Hemiptera: Coccidae) containing a pupa (black) of a wasp (Hymenoptera) parasitoid. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T85]

The upper side (left) and underside (right) of a wasp (Hymenoptera) parasitoid that emerged from an adult female Soft wax scale, Ceroplastes destructor (Hemiptera: Coccidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T86]

Three images of the upper side of a wasp (Hymenoptera) parasitoid that emerged from an adult female Soft wax scale, Ceroplastes destructor (Hemiptera: Coccidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T87]

Adult steelblue ladybird, Halmus chalybeus (Coleoptera: Coccinellidae), about 4 mm long. Creator: Tim Holmes. © Plant & Food Research. [Image: 15VZ]

Mature larva of steelblue ladybird, Halmus chalybeus (Coleoptera: Coccinellidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 15W1]

Adult Forestier's ladybird, Rhyzobius forestieri (Coleoptera: Coccinellidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2D70]

Larva of Forestier's ladybird, Rhyzobius forestieri (Coleoptera: Coccinellidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2D6Y]

Soft wax scale are found mainly on cultivated and naturalised plants, and sometimes on native plants. Occasionally it can reach high numbers. The small nymphs are mainly found on the upper side of leaves, while the egg laying females are mostly on stems.

Feeding and honeydew

Like other Hemiptera, the adult female and nymphs of Soft wax scale 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 adult females and nymphs of Soft wax scale insert their 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. Sooty moulds may grow on the honeydew.

Adult female Soft wax scales, Ceroplastes destructor (Hemiptera: Coccidae) on stems of Syzygium sp. (Myrtaceae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 2T8P]

Third instar nymphs and adult female Soft wax scales, Ceroplastes destructor (Hemiptera: Coccidae) on stems of Syzygium sp. (Myrtaceae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 2T8K]

Adult female Soft wax scale, Ceroplastes destructor (Hemiptera: Coccidae) on stem of Syzygium sp. (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T8J]

Young nymphs of Soft wax scales, Ceroplastes destructor (Hemiptera: Coccidae) on leaves and a young stem of Syzygium sp. (Myrtaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T7Y]

Third instar nymphs of Soft wax scales, Ceroplastes destructor (Hemiptera: Coccidae) on stems of Syzygium sp. (Myrtaceae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 2T8L]

Third instar (stage) nymphs of Soft wax scale, Ceroplastes destructor (Hemiptera: Coccidae) on stems of Tahiti lime, Citrus aurantiifolia (Rutaceae): note the forward pointing ‘horn’ of white wax. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T88]

Soft wax scale, Ceroplastes destructor (Hemiptera: Coccidae) on stems of Gardenia, Gardenia sp. (Rubiaceae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 2T8N]

The adult females and nymphs of Soft wax scale insert their 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. Sooty moulds may grow on the honeydew.

Worker ants (Hymenoptera: Formicidae) have been found associated with Soft wax scale and are assumed to have been feeding on honeydew.

Two worker ants (Formicidae: Hymenoptera) feeding on honeydew produced by Soft wax scale, Ceroplastes destructor (Hemiptera: Coccidae) living on Gardenia, Gardenia sp. (Rubiaceae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 2T8M]

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.