INTERESTING INSECTS

By N A Martin (2018)

Marble leaf erineum mite, Putaputaweta leaf erineum mite

This endemic gall mite has been found in the North and South Islands of New Zealand on its host plant, Marble leaf, Carpodetus serratus (Rousseaceae). The mite induces white hairs, erineum, on the upper and/or underside of leaves.

Conservation status: Not threatened.

This gall mite is very tiny. Adult female mites are about, 0.101-0.162 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 the 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 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 an erineum on leaves of Marble leaf, Carpodetus serratus (Rousseaceae). The erineum may be induced on the upper or underside of young leaves. Old erineum turns brown and some leaves may turn yellow on the other side of the leaf.

Erineum on other plants is caused by other species of mite.

No natural enemies of this species of mite have been recorded, but predatory mites and predatory gall fly larvae may feed on these mites. A red hairy fly larva that has been found on one patch of erineum could be a predator of these gall mites.

The Marble leaf erineum mite is only found on leaves of Marble leaf, Carpodetus serratus (Rousseaceae). The mites have pointed mouth parts that puncture the surface cells of young leaves. Their feeding induces the plant to grow white hairs that are called erineum. The erineum is found in patches on either side of leaves. The older erieneum becomes brown.

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.