INTERESTING INSECTS

By N A Martin (2017)

Puriri domatia gall mite

Eriophyes hodgkinsi Manson, 1965

Phyllocoptes hodgkinsi (Manson, 1965)

This endemic gall mite is found in New Zealand where its host plant, puriri, Vitex lucens Kirk (Labiatae) grows. The mite induces leaf domatia galls.

Conservation status: Widespread, not threatened.

This gall mite is very tiny. Adult mites are about 0.2 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.

The mites live in domatia and induce the formation of domatia galls. Domatia are structures formed at the junction between side veins and the main central vein on leaves of some species of plants. In puriri, the domatia is a cavity.

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 inducing the gall

The mites have pointed mouth parts that puncture the surface cells 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 leaf cells in domatia, they multiply causing a thickening and expansion of the domatia. The walls thicken around an enlarged cavity and the domatia opening narrows. The enlarged domatia can be seen as protuberances on both sides of the leaf. The mites shelter, feed and breed inside the gall. The gall protects the gall mites from predators and adverse weather.

Dispersal to new stems and new plants

When the plant grows new shoots, adult female mites disperse to the new leaves and their feeding in domatia induces the formation of new galls. It is presumed mites walk from the old galls to the new leaves.

When this gall mite colonises new plants, 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 mite species is the only one known to induce domatia galls on leaves of puriri, Vitex lucens. Domatia galls on other plants are caused by other mite species.

No natural enemies of this mite have been recorded, but predatory mites may feed on these gall mites, especially when they are dispersing to new host plant leaves.

Puriri domatia gall mite, Asetilobus hodgkinsi (Acari: Eriophyidae), is one of three species of gall mite that lives on puriri, Vitex lucens Kirk (Labiatae). It is the only mite inducing and living in domatia galls on puriri leaves. Domatia are structures formed at the junction between side veins and the main central vein on leaves of some species of plants. In puriri, the domatia is a cavity. When the mite feeds on leaf cells in domatia, they multiply causing a thickening and expansion of the domatia. The walls thicken around an enlarged cavity and the domatia opening narrows. The enlarged domatia can be seen as protuberances on both sides of the leaf.

Eriophyid mites

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.

Domatia

Domatia are structures formed at the junction between side veins and the main central vein on leaves of some species of plants. They may consist of tufts of hairs in the V or covering the space formed at the junction of the veins. In some plants such as puriri, the domatia is in the form of a cavity. One explanation for the formation of domatia is that they provide shelter for predatory mites that then prevent damage to the leaf by plant feeding mites. However, in New Zealand at least two kinds of plant feeding mites live in domatia. These include gall mites (Eriophyoidea) and ‘spider’ mites (Tetranychidae). Domatia galls induced by gall mites are found on puriri, Vitex lucens Kirk (Labiatae) that are induced by puriri domatia gall mite, Asetilobus hodgkinsi (Acari: Eriophyidae), and on several species of Coprosma (Rubiaceae) induced by Acalitus intertextus Manson, 1984 (Eriophyidae). The galls of this species are most commonly seen on Coprosma lucida J.R. et G. Forst. On hinau, Elaeocarpus dentatus (J.R.Forst. & G.Forst.) Vahl and Elaeocarpus hookerianus Raoul (Elaeocarpaceae), a mite, Neonidulus cornus (Pritchard & Baker, 1967) (Tetranychidae), lives in the domatia and covers the entrance with a thin white web.

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

Norton AP, English-Loeb G 2001. Host plant manipulation of natural enemies: leaf domatia protect beneficial mites from insect predators. Oecologia 126: 535-542.

Romero GQ, Benson WW 2005. Biotic interactions of mites, plants and leaf domatia. Current Opinion in Plant Biology 8(4): 436-440.

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