INTERESTING INSECTS

By N A Martin (2018)

Puriri erineum mite, Puriri leaf mite

Aceria australis Lamb, 1952

is endemic gall mite is found in the North Island of New Zealand where its host plant, Puriri, Vitex lucens (Labiatae) grows. Feeding by the mites induces white hairs (erineum) on the underside of leaves.

Conservation status: Present in the North Island where Puriri trees grow.

This gall mite is very tiny. Adult mites are about 0.114-0.174 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. Adult female mites lay tiny spherical eggs. 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 it can also hold on to the plant with the tip of its abdomen, which acts as a sucker.

Feeding and inducing the gall

The mites have pointed mouth parts that puncture the surface cells on the underside of young leaves and gall tissue from which they suck up the cell sap. During feeding, the mites may inject saliva into the plant. When mites feed on the underside of a young leaf, plant cells in the immediate area multiply forming a white hairy tissue (erineum) in which the mites live and breed. The erineum protects the gall mites from predators and adverse weather.

Dispersal to new leaves and new trees

When the plant grows new shoots, adult female mites disperse to the new leaves and their feeding induces the formation of new galls, erineum. It is presumed that mites walk from the old erineum to young leaves suitable for the initiation of new erineum.

When this gall mite colonises new plants or branches, it is unlikely that mites walk all the way. 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 by plant damage symptoms. This species of mite is the only one known to induce erineum on leaves of Puriri, Vitex lucens (Labiatae). The upper surface of the leaf above areas of erineum, bulge upwards and may be chlorotic (coloured yellow). The erineum on older leaves turns brown.

One predatory mite, Agistemus longisetus Gonzalez-Rodriguez, 1963 (Acari: Raphignathoidea: Stigmaeidae) has been found on Puriri leaves in association with leaf erineum. It is presumed that this predator feeds on the Puriri erineum mite. Other predatory mites and predatory insects may also feed on these gall mites.

Puriri, Vitex lucens (Labiatae) is the only host plant of the Puriri erineum mite. The mite feeds on the underside young leaves. When mites feed on the underside of a young leaf, plant cells in the immediate area multiply forming a white hairy tissue (erineum) in which the mites live and breed.

Eriophyid gall mites belong to the super family Eryiophyoidea. These mites have several unusual features. For example, though most mites have four pairs of legs like spiders, Eriophyoid mites have only two pairs of legs. Many of these mites can induce 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.

Manson DCM 1984. Eriophyinae (Arachnida: Acari: Eriophyoidea). Fauna of New Zealand 5: 1-123.

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