INTERESTING INSECTS

By N A Martin (2017)

Totara bud mite

This endemic gall mite is uncommon, but has been found in the North and South Islands of New Zealand. It occurs on its host plant, Totara, Podocarpus totara (Podocarpaceae), in city gardens and presumably in native ecosystems. Feeding by the mites induces a bud gall.

Conservation status: Widespread, not threatened.

This gall mite is very tiny. Adult mites are 0.138-0.166 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 look a tiny 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 can also hold on to the plant with the tip of its abdomen which acts as a sucker.

Feeding and forming the gall

The mites have pointed mouth parts that puncture the surface cells of bud scales, tiny leaves within buds and male flower cones. They suck up the cell sap. During feeding, the mites may inject saliva into the plant. The bud scales enlarge and spaces develop between the scales in which the mites live. The mites shelter in the gall and feed and breed there. The gall protects the gall mites from predators and adverse weather.

Dispersal to new stems and new plants

When the plant grows new shoots with buds, adult female mites disperse to these and their feeding induces the formation of new galls. It is presumed some mites walk from the old galls to the new growths.

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 from associated plant damage symptoms. This mite species is the only one known to induce bud galls and live in male cones of totara, Podocarpus totara. A gall fly (Diptera: Cecidomyiidae) also induces bud galls on Podocarpus species. It can be distinguished by the presence of fly larvae in the gall and by the bud scales remaining closed on the enlarged bud.

No natural enemies of this mite have been reported.

Totara bud mite has only been found on totara, Podocarpus totara G. Benn. ex D. Don (Podocarpaceae), though it may live on other Podocarpus species. The mite induces galls in vegetative buds and buds of male flower cones. The mite can also live in open cones. Mite feeding in a bud induces the bud scales enlarge and spaces develop between the scales in which the mites live.

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, 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.

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.