INTERESTING INSECTS

By N A Martin (2010, revised 2018)

Coprosma white erineum mite

This endemic gall mite has been found in the North and South Islands of New Zealand. It occurs on host plants, Coprosma species, in city gardens and parks as well as native ecosystems. The mite induces white hairs, erineum, on the underside of leaves.

Conservation status: Widespread, not threatened.

This gall mite is very tiny. Adult mites are 0.13-0.18 mm long. The adult mite is like a tiny white cow's horn with two pairs of legs at the wide end of the horn. The female mite lays a tiny spherical egg. The larva that hatches from an egg looks like a tiny adult. The mite larva moults (changes skin) into a nymph. There is one nymphal stage that also looks like a small adult. The last juvenile stage moults into an adult mite. There are males and females.

Walking

The mite uses its legs for walking, but can also hold on to the plant with the tip of its abdomen, which appears to act as a kind of sucker.

Feeding and forming the erineum gall

The mites have pointed mouth parts that puncture the surface cells of plant leaves. They suck up the cell contents. During feeding, the mites may inject saliva into the plant. When this happens on young expanding leaves, chemicals in the saliva induce the plant to grow hairs on the leaf surface. These growths form the gall called an 'erineum'. The mites shelter amongst the hairs and feed and breed there. The erineum protects the gall mites from predators. The gall may also maintain a high humid atmosphere around the mites.

Dispersal to new leaves and plants

When the plant grows new shoots, adult female mites disperse to the new leaves and their feeding causes a new erineum to form. It is presumed some mites walk from the old leaves to the new growths. When this gall mite colonises new plants, it is unlikely that mites walk all the way. It is possible that mites could be transferred on leaves, but it is believed that most mites are dispersed by wind. Some species of mite climb to prominent places on plants and stand waiting for a gust of wind to take them away.

This mite requires special procedures and taxonomic knowledge to identify specimens. However, its presence on a plant can be recognised from associated plant damage symptoms. This mite species is the only one known to induce a white erineum in Coprosma leaves. White erineum in other plants is caused by other mite. A black erineum and a brown erineum have been found on other Coprosma species; they are believed to be caused by different mite species.

No natural enemies of this mite have previously been recorded, but a fly larva (Diptera: Cecidomyiidae) was observed feeding on eggs of another erineum mite. Similar fly larvae were seen on young leaves with erineum. Predatory mites from several different taxonomic groups may be seen on plant leaves with erineum, and may feed on these mites. Eggs of the Steelblue ladybird, Halmus chalybeus, were found on a leaf with erineum. This ladybird is known to feed on eriophyid mites.

Table: Predators of Coprosma white erineum mite, Phyllocoptes coprosmae (Acari: Prostigmata: Eriophyidae), from Plant-SyNZ databa se (20 December 2016). The reliability index shows the quality of evidence for the host association (0-10, 10=high quality).

Scientific Name	Common Name	Classification	Enemy Type	Reliability Index	Biostatus
Bdellidae sp.	Bdellid mite (Mite)	Acari: Prostigmata: Bdellidae	predator	5	unknown
Cecidomyiidae sp. 'predators'	(Fly)	Diptera: Cecidomyiidae	predator	5	unknown
Halmus chalybeus (Boisduval, 1835)	Steelblue ladybird (Beetle)	Coleoptera: Coccinellidae	predator	7	adventive

White leaf erineum is found on many species of Coprosma, especially the larger leaved species. It usually occurs on the underside of leaves, though in some Coprosma species it may extend to the upper surface. In some plants, the upper side of the leaf may be chlorotic (yellow) above the site of the erineum. On larger leaved plants, the erineum is in discrete patches, but may extend over the whole leaf.

Table: Host plants of the Coprosma white erineum mite, Phyllocoptes coprosmae (Acari: Prostigmata: Eriophyidae) from Plant-SyNZ database (10 July 2018). The reliability score shows the quality of evidence for the host association (1-10, 10=high).

Common Name(s)	Scientific Name	Family	Reliability Index	Biostatus
Tree coprosma, Mamangi, Māmāngi	Coprosma arborea Kirk	Rubiaceae	9	endemic
	Coprosma dumosa (Cheeseman) G.T.Jane	Rubiaceae	9	endemic
Stinkwood, Hūpirau-ririki, Hūpiro, Karamū, Mikimiki, Mingimingi, Naupiro, Pipiro, Piro	Coprosma foetidissima J.R.Forst. & G.Forst.	Rubiaceae	9	endemic
Kākawariki, Kanono, Kapukiore, Karamū-kueo, Kueo (fruit), Manono, Pāpāuma, Raurēkau, Toherāoa	Coprosma grandifolia Hook.f.	Rubiaceae	9	endemic
Shining karamu, Kākaramū, Kākarangū, Karamū, Kāramuramu, Karangū, Patutiketike	Coprosma lucida J.R.Forst. & G.Forst.	Rubiaceae	9	endemic
	Coprosma macrocarpa Cheeseman subsp. minor A.P.Druce ex R.O.Gardner & Heads (2003)	Rubiaceae	9	endemic
Coastal Coprosma, Taupata	Coprosma repens A.Rich.	Rubiaceae	9	endemic
Twiggy Coprosma	Coprosma rhamnoides A.Cunn.	Rubiaceae	9	endemic
Glossy karamu, Kākaramū, Kākarangū, Karamū, Kāramuramu, Karangū	Coprosma robusta Raoul	Rubiaceae	10	endemic
Round-leaved coprosma	Coprosma rotundifolia A.Cunn.	Rubiaceae	9	endemic
	Coprosma rubra Petrie	Rubiaceae	9	endemic
Wavy-leaved coprosma	Coprosma tenuifolia Cheeseman	Rubiaceae	9	endemic
	Coprosma virescens Petrie	Rubiaceae	9	endemic

Eriophyid gall mites belong to the superfamily Eryiophyoidea. These mites have several unusual features. For example, though most mites have four pairs of legs like spiders, Eriophyoidea mites have only two pairs of legs. Many of these mites can cause host plants to form galls, some of which may be very complex. Some species of these mites can transmit plant viruses that may cause plant diseases and plant death.

Metal outdoor signs are available for placement in reserves, Regional and National parks, urban parks and school grounds. They can be bought from Metal Images Ltd, www.metalimage.co.nz/products/botanic-labels. The Bug Signs are listed near the bottom of the 'Fauna Species list'. The signs come in two sizes, 100 x 200 mm, 194 x 294 mm. The signs can be bought ready mounted on a stand that needs to be 'planted' in the ground, or they can be bought unmounted with holes for fixing into your own mounts.

The signs for the Coprosma white erineum mite are best placed by a bush with erineum galls. Look for a bush with yellow patches on the upper side of leaves, then check if there are patches of erineum on the underside. New erineum should be formed on young leaves every year.

Manson DCM 1984. Eriophyoidea except Eriophyinae (Arachnida: Acari). Fauna of New Zealand 4: 1-142..

Plant-SyNZ: Invertebrate herbivore-host plant association database. plant-synz.landcareresearch.co.nz/.

Eric Scott for helpful suggestions.

The New Zealand Plant & Food Research Institute Limited (Plant & Food Research) for permission to use photographs.

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

1 December 2018. NA Martin. Changed symbol used for apostrophes.

1 August 2018, NA Martin. Host list updated, Photos added.

1 April 2018. NA Martin. Bug signs updated

1 August 2017. NA Martin. New photographs of erineum.

21 December 2016. NA Martin. Updated natural enemy table.

5 April 2016. NA Martin. Life Stages: juvenile stages revised. Recognition: added photos of white erineum and chlorotic areas on leaves, and photos of Steelblue ladybird eggs and larvae. Host plants: figure caption for C. grandifolia amended