INTERESTING INSECTS

By N A Martin (2018 revised 2019)

Long egg-sac mealybug

Dactylopius glaucus Maskell, 1879

Pseudococcus glaucus (Maskell, 1879)

Trionymus morrisoni Brittin, 1938

Paracoccus morrisoni (Brittin, 1938)

The endemic Long egg-sac mealybug lives on ferns and leaves of trees and shrubs in the North & South Islands. As its name suggests it has distinctive long egg sacs.

Conservation status: This native mealybug is not endangered and is found in native ecosystems in the North & South Islands.

Diagramme of the life cycle of a typical mealybug (Hemiptera: Pseudococcidae). Creator: JM Cox. © Drawing published in Fauna of New Zealand 11:1-228, Fig. 1. [Image: 2F19]

The Long egg-sac mealybug appears to breed all year. There do not appear to be discrete generations. It is not known how long it takes from egg to adult. All stages live on the leaves of its host plants.

The adult female is oval, about 3-4 mm long and 2 mm wide. The body varies from pale green to orange-red with a darker line by the midline. The body is lightly covered with powdery white wax. There is a terminal pair of white wax filaments, and smaller white wax filaments at the front and along the edge of the abdomen. The mature female has a pair of short antennae and three pairs of legs. There is no distinct division between the head or thorax (middle section of the body) and abdomen. On the underside of the head there is a short rostrum that guides the feeding stylets. After mating and when it is fully grown, the female mealybug settles on a leaf and produces a white fluffy wax chamber at the rear end of its body. It lays orange coloured eggs into the egg sac. As it fills up, the female mealybug moves forward making the sac longer as it continues to lay more eggs. The female body gradually shrinks and the white wax covering becomes denser.

Nymphs hatch from the eggs and leave the egg sac. The nymphs are like small orange-brown adult females. There are three female nymphal instars (stages) and two male nymphal instars. These feeding stages grow by moulting (changing skin). The second instar male makes a fluffy white cocoon in which develop two pre-adult non-feeding stages, a prepupa and a pupa. The prepupa and pupa have wing buds. The adult male emerges from the pupa. The moulted prepupal and pupal skins are pushed out the end of the cocoon. The adult male does not have a rostrum or stylets and does not feed. When it is ready to emerge from the cocoon, the back end of the cocoon is pushed open and the male backs out. After it has opened the back of the cocoon, its wings (1 pair) expand and harden. It also grows a pair of long wax tails. It is presumed that the wax tails help balance the insect in flight. The male may mate with females of the same colony or fly to another colony to mate.

Feeding and honeydew

Mealybug adult females and nymphs have sucking mouthparts. Specially shaped rods called stylets are held in the short sheath-like rostrum. When it wishes to feed, the mealybug moves the tip of the rostrum onto the surface of the plant leaf or stem. The stylets are then gradually pushed into the plant and manoeuvred into the phloem (nutrient transport vessels) of the plant. The mealybugs suck the plant’s sap, which is high in sugars and low in other nutrients. Mealybugs have a short white wax anal tube through which they excrete the excess sugary liquid, which is called honeydew.

Walking, flying and dispersal

The adult male has legs and wings. It can walk around the leaves where its cocoon was and it can fly to other leaves or to different trees. Adult females and nymphs also have legs and can walk. They may move about the group of leaves where they were born. In other insects with a none flying adult female, the first stage larvae or nymphs are able to disperse to new trees. They usually do this using the wind. It is likely that some first instar nymphs climb to a prominent place on a leaf or branch and await a gust of wind.

Two female Long egg-sac mealybugs, Paracoccus glaucus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae): note the pair of white wax tails. Creator: Tim Holmes. © Plant & Food Research. [Image: 2RE0]

Female Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae): note short egg sac forming behind the female. Creator: Tim Holmes. © Plant & Food Research. [Image: 2RE3]

A female Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae) with a short egg sac and on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2RE4]

A female Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae) with an egg sac and first instar (stage) nymphs on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae): note the white wax covering the old female. Creator: Tim Holmes. © Plant & Food Research. [Image: 2RE5]

An old egg sac of the Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae): note the white wax covering the dead female. Creator: Tim Holmes. © Plant & Food Research. [Image: 2RE6]

Nymphs arround an old egg sac of the Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae). Most of the nymphs are second instar (stage): note the white moulted skins. Creator: Tim Holmes. © Plant & Food Research. [Image: 2RE7]

Nymphs arround an old egg sac of the Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae): note the white moulted skins. Creator: Tim Holmes. © Plant & Food Research. [Image: 2RE9]

White male cocoons of the Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2RE8]

White male cocoons of the Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae): note the wings and white wax tail protruding from the bottom left cocoon. Creator: Tim Holmes. © Plant & Food Research. [Image: 2RE2]

Adult male Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2REC]

An underside of an adult male Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2REF]

Side view of an adult male Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2RED]

An adult male on cocoons of the Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2REA]

Mealybugs (Pseudococcidae) require specialist skills for their identification. However, when some species are on their host plants they have distinct features that enables them to be named with confidence. The Long egg-sac mealybug is one such species. The oval adult females are pale green to orange-red, with a darker line by the midline. The body is lightly covered with powdery white wax and has short filaments of white wax at the front and back with one pair of strong white wax filaments at the back. The other distinguishing feature is the long egg sac made by the female.

The mealybug, Paracoccus zealandicus (Ezzat & McConnell, 1956) has some similarities to Long egg-sac mealybugs. Notably they have the same white wax filaments at the front and back and a thin powdery white wax covering of the body. However, the underlying colour of Paracoccus zealandicus dark purplish-brown.

An adult female and nymphs of Long egg-sac mealybugs, Paracoccus glaucus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae): note the pair of white wax tails. Creator: Tim Holmes. © Plant & Food Research. [Image: 2RE1]

A female Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae) with an egg sac and first instar (stage) nymphs on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae): note the white wax covering the old female. Creator: Tim Holmes. © Plant & Food Research. [Image: 2RE5]

An adult female, nymphs and an adult male probably of Long egg-sac mealybugs, Paracoccus glaucus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae): note the pair of white wax tails and the reddish colour of the adult female and large nymphs. Creator: Tim Holmes. © Plant & Food Research. [Image: 2REB]

Two adult females and an adult male of Long egg-sac mealybugs, Paracoccus glaucus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 2REJ]

No pathogens of the Long egg-sac mealybug, Paracoccus glaucus are known.

Parasitoids

One parasitoid wasp (Hymenoptera) has been reared from Long egg-sac mealybugs.

Predators

Several predators have been observed feeding on the mealybugs. These include three species of ladybird (two adventive and one endemic species) and larvae of two kinds of flies, predatory gall flies (Cecidomyiidae) and hoverflies (Syrphidae). The predatory Red-cross mirid has also been found associated with mealybug colonies.

Larva of a predatory gallfly, Cecidomyiidae sp. 'predators' (Diptera: Cecidomyiidae) feeding on Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2RDH]

Larva of a predatory gallfly, Cecidomyiidae sp. 'predators' (Diptera: Cecidomyiidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2RDI]

Larva of a predatory gallfly, Cecidomyiidae sp. 'predators' (Diptera: Cecidomyiidae) feeding on Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RDS]

Larva of a predatory gallfly, Cecidomyiidae sp. 'predators' (Diptera: Cecidomyiidae) feeding on Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RDT]

Cocoon being made by a larva of a predatory gallfly, Cecidomyiidae sp. 'predators' (Diptera: Cecidomyiidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae) after feeding on Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2RDJ]

Cocoon being made by a larva of a predatory gallfly, Cecidomyiidae sp. 'predators' (Diptera: Cecidomyiidae) after feeding on Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2RDK]

Cocoon being made by a larva of a predatory gallfly, Cecidomyiidae sp. 'predators' (Diptera: Cecidomyiidae) after feeding on Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2RDL]

Cocoon of a predatory gallfly, Cecidomyiidae sp. 'predators' (Diptera: Cecidomyiidae) after feeding on Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2RDN]

Pupa exposed by opening cocoon of a predatory gallfly, Cecidomyiidae sp. 'predators' (Diptera: Cecidomyiidae) after feeding on Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2RDP]

Empty pupal case protruding from cocoon of a predatory gallfly, Cecidomyiidae sp. 'predators' (Diptera: Cecidomyiidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae). When the adult is ready to emerge, the pupal protrudes from one end of the cocoon. Creator: Tim Holmes. © Plant & Food Research. [Image: 2RDM]

Empty pupal case protruding from cocoon of a predatory gallfly, Cecidomyiidae sp. 'predators' (Diptera: Cecidomyiidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2RDR]

Adult predatory gallfly, Cecidomyiidae sp. 'predators' (Diptera: Cecidomyiidae) whose larva had fed on Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2RDQ]

Larva of a Hoverfly, Syrphidae sp. (Diptera: Syrphidae) feeding on Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2REG]

Larva of a Hoverfly, Syrphidae sp. (Diptera: Syrphidae) feeding on Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2REH]

Larvae of mealybug ladybird, Cryptolaemus montrouzieri (Coleoptera: Coccinellidae), feeding on Long egg-sac mealybug, Paracoccus glaucus (Hemiptera: Pseudococcidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2CDN]

Adult mealybug ladybird, Cryptolaemus montrouzieri (Coleoptera: Coccinellidae). © Plant & Food Research. [Image: 2863]

A fully grown larva of mealybug ladybird, Cryptolaemus montrouzieri (Coleoptera: Coccinellidae) eating a small mealybug (left). © Plant & Food Research. [Image: 2CDZ]

Larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZC]

Larva of Native mealybug ladybird, Rhyzobius sp. 1 (Coleoptera: Coccinellidae) feeding on mealybugs on kawakawa (Piper excelsum). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DX0]

Larva of Native mealybug ladybird, Rhyzobius sp. 1 (Coleoptera: Coccinellidae) feeding on mealybugs on kawakawa (Piper excelsum). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DX1]

Adult Native mealybug ladybird, Rhyzobius sp. 1 (Coleoptera: Coccinellidae) about 2 mm long. Creator: Tim Holmes. © Plant & Food Research. [Image: 2DWS]

The Long egg-sac mealybug lives on ferns, shrubs, trees and climbers. It is mainly found on indigenous plants, by has been found on cultivated and naturalised species. It mainly lives on the underside of leaves, but on Puriri, Vitex lucens (Labiatae), nymphs may be found on the upper side of leaves, especially along the midrib. The young mealybugs often settle by against something prominent on the leaf. The most distinctive characteristic of this species is the long, often coiled egg sac made on the underside of leaves by the female mealybug.

Feeding and honeydew

Mealybug adult females and nymphs have sucking mouthparts. Specially shaped rods called stylets are held in the short sheath-like rostrum. When it wishes to feed, the mealybug moves the tip of the rostrum onto the surface of the plant leaf or stem. The stylets are then gradually pushed into the plant and manoeuvred into the phloem (nutrient transport vessels) of the plant. The mealybugs suck the plant’s sap, which is high in sugars and low in other nutrients. Mealybugs have a short white wax anal tube through which they excrete the excess sugary liquid, which is called honeydew.

Long egg-sac mealybugs, Paracoccus glaucus (Hemiptera: Pseudococcidae) on underside of fronds of Lance fern, Loxogramme dictyopteris (Polypodiaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RDU]

Long egg-sac mealybugs, Paracoccus glaucus (Hemiptera: Pseudococcidae) on the underside of a leaf of Mahoe, Melicytus ramiflorus (Violaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RDV]

Long egg-sac mealybugs, Paracoccus glaucus (Hemiptera: Pseudococcidae) on the underside of a leaf of Mahoe, Melicytus ramiflorus (Violaceae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 2REK]

Long egg-sac mealybugs, Paracoccus glaucus (Hemiptera: Pseudococcidae) on the underside of a leaf of Supplejack, Ripogonum scandens (Ripogonaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RDW]

Juvenile Long egg-sac mealybugs, Paracoccus glaucus (Hemiptera: Pseudococcidae) on the upper side of a leaf of Puriri, Vitex lucens (Labiatae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RDX]

Long egg-sac mealybugs, Paracoccus glaucus (Hemiptera: Pseudococcidae) on young leaves of Kiekie, Freycinetia banksii (Pandanaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RDY]

Long egg-sac mealybugs, Paracoccus glaucus (Hemiptera: Pseudococcidae) on a mature leaf of Kiekie, Freycinetia banksii (Pandanaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RDZ]

Long egg-sac mealybugs, Paracoccus glaucus (Hemiptera: Pseudococcidae) on the underside of a leaf of Hangehange, Geniostoma ligustrifolium (Loganiaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2REI]

Long egg-sac mealybugs, Paracoccus glaucus (Hemiptera: Pseudococcidae) on the underside of a leaf of Kawakawa, Piper excelsum (Piperaceae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 2REL]

Why is there so much white wax?

Most mealybugs produce much white flocculent wax with which they are covered and which also covers the areas of plants they inhabit. To the human eye this makes it much easier to find the colonies of mealybugs. However, does it make it easier for predators and parasitoids to find them, or is the white wax some kind of deterrent and warning colouration? Other insects with a scale stage also cover themselves with white wax. This suggests to me that it may be some kind of deterrent and warning.

Research Project: Colour variation of adult females

Jenifer Cox in her 1987 paper on the taxonomy of New Zealand Mealybugs discusses the similarity between the Long egg-sac mealybug, Paracoccus glaucus and Paracoccus zealandicus (Ezzat & McConnell, 1956). Both are oval shaped, covered by thin powdery white wax and have the same wax filaments at the front and back. The main difference between live adult females is that the underlying colour of P. zealandicus are dark purplish brown, while those of the Long egg-sac mealybug are pale, bright green, or sometimes a pale, bright orange. These colour differences were used to determine the taxonomic characters used to distinguish the two species. Jenifer thought that further studies, particularly host-transfer experiments, may change this interpretation. This problem seems to me to be a good candidate for the use of molecular biology.

An adult female and nymphs of Long egg-sac mealybugs, Paracoccus glaucus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae): note the pair of white wax tails. Creator: Tim Holmes. © Plant & Food Research. [Image: 2RE1]

An adult female, nymphs and an adult male probably of Long egg-sac mealybugs, Paracoccus glaucus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae): note the pair of white wax tails and the reddish colour of the adult female and large nymphs. Creator: Tim Holmes. © Plant & Food Research. [Image: 2REB]

Cox JM. 1987. Pseudococcidae (Insecta: Hemiptera). Fauna of New Zealand. 11: 1-230.

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.

1 October 2019, NA Martin, Two Browse items corrected.