INTERESTING INSECTS

By N A Martin (2017)

New Zealand beech bud-mite, Nothofagus big bud mite

This endemic gall mite is found in the North and South Islands of New Zealand on its host plants, southern beech trees in the genus Fuscospora (Nothofagaceae), black beech, hard beech, mountain beech and red beech. Feeding by the mites induces enlarged buds. The northern most populations of Fuscospora species are in Auckland, in forest remnants on the north side of the Waitemata harbour.

Conservation status: Widespread, not threatened.

This gall mite is very tiny. Adult mites are about 0.138-0.186 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 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 in a leaf bud, the cells of the bud scales in the immediate area multiply forming a hairy spongy tissue in which the mites live and breed. The bud scales also grow bigger forming a large round bud. The enlarged bud 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 these and their feeding induces the formation of new galls. It is presumed mites walk from the old bud galls to new buds.

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 large bud galls on trees in the genus Fuscospora (Nothofagaceae) species in New Zealand. Bud galls on other species of plant are caused by other species of mite or other insects.

No natural enemies of this mite have been recorded, but predatory mites may feed on these mites.

New Zealand beech bud-mite, Acalitus morrisoni (Acari: Eriophyidae), lives in enlarged buds on four species of Fuscospora (Nothofagaceae) growing in New Zealand. Mites feeding in young leaf buds induce the cells of the bud scales in the area to multiply forming hairy spongy tissue in which the mites live and breed. The bud scales also grow bigger forming a large round bud in contrast to the normal narrow pointed buds. The mites appear to colonise a terminal bud in the current year’s new growth. The enlarged bud has a short wide stem with what appears to be scars of bud scales. This indicates that as the mite colony grows and new bud scales grow as the outer scales die and fall off.

Table: Host plants of the New Zealand beech bud-mite, Acalitus morrisoni (Acari: Prostigmata: Eriophyidae) from Plant-SyNZ database (26 February 2017). 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
Mountain beech, Tawhai rauriki	Fuscospora cliffortioides (Hook.f.) Heenan & Smissen	Nothofagaceae	10	endemic
Red beech, Hutu, Hututawai, Raunui, Tawai, Tawhai	Fuscospora fusca (Hook.f.) Heenan & Smissen	Nothofagaceae	10	endemic
Black beech, Tawhai rauriki	Fuscospora solandri (Hook.f.) Heenan & Smissen	Nothofagaceae	10	endemic
Hard beech, Hutu, Hututawai, Tawhai raunui	Fuscospora truncata (Colenso) Heenan & Smissen	Nothofagaceae	10	endemic

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.