INTERESTING INSECTS

By N A Martin (2018)

Poroporo gall mite, Poroporo russet mite

This endemic gall mite was first found in 1980 on leaves of one of its two host plants, Poroporo, Solanum aviculare (Solanaceae). The infected plants were near New Plymouth and were being grown for pharmaceutical steroids. Feeding on young leaves causes russeting and distortion. It has also been found in Auckland and on Solanum laciniatum. It is present in gardens and native habitats.

Conservation status: Probably widespread, where its host plants are present.

This gall mite is very tiny. Adult mites are about 0.182-0.202 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 their 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 leaf damage

The mites have pointed mouth parts that puncture the surface cells of young leaves from which they suck up the cell sap. During feeding, the mites may inject saliva into the plant. Mite feeding is associated with distortion of young leaves and may be associated with both physical damage to young cells and from injection of mite saliva.

Dispersal to new shoots and new plants

When the plant grows new leaves, adult female mites disperse to these and their feeding causes leaf damage. It is presumed mites walk from the older leaves 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 by plant damage symptoms. This mite species is the only one known to cause leaf russeting and distortion of young leaves of Poroporo, Solanum aviculare and Solanum laciniatum (Solanaceae).

No natural enemies of the Poroporo gall mite have been observed. A possible predatory mite (Acari, Phytoseiidae) has been seen in a colony of the gall mites.

Poroporo gall mite is known from Poroporo, Solanum aviculare and Solanum laciniatum (Solanaceae). It feeds on the young leaves.

Feeding and plant damage

The mites have pointed mouth parts that puncture the surface cells of young leaves from which they suck up the cell sap. During feeding, the mites may inject saliva into the plant. Mite feeding is associated with distortion of young leaves and may be associated with both physical damage to young cells and from injection of mite saliva.

Table: Host plants of the Poroporo gall mite, Tetra martini (Acari: Prostigmata: Eriophyidae) from Plant-SyNZ database (24 November 2018). 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
Bullibul, Bullibulli, Kangaroo apple, Pōpopo, Poroporo, Poroporotanguru	Solanum aviculare G.Forst.	Solanaceae	10	indigenous, non-endemic
Bullibul, Bullibulli, Large kangaroo apple, Pōpopo, Poroporo, Poroporotanguru	Solanum laciniatum Aiton	Solanaceae	9	indigenous, non-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. Eriophyoidea except Eriophyinae (Arachnida: Acari). Fauna of New Zealand. 4: 1-142.

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

Landcare Research New Zealand Limited (Landcare Research) for permission to use photographs.