INTERESTING INSECTS

By N A Martin (2018)

Kaka beak gall mite

This endemic gall mite is found on wild Kaka beak, Clianthus species (Leguminosae) in the North Island. It is also found on cultivated plants in both the North and South Islands of New Zealand.

Conservation status: The mite is threatened with extinction in the wild along with its host plants.

This gall mite is very tiny. Adult female mites are about, 0.156-0.249 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 galls

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. In the area where the mites are feeding the leaf and bud growth becomes distorted. When multiple buds develop producing a cluster of short stems, this is called a witch's broom. On larger expanding leaves, mite feeding may induce the leaflet edge to fold over. The mites shelter in the gall and breed there. The galls protect 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 shoots and their feeding causes new galls 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 a witch's broom galls and distorted leaves on plant of Kaka beak, Clianthus species (Leguminosae). The galls may be induced on young leaves and shoots.

Similar galls on other plants are caused by other species of mite, insect or microorganism.

Three predators of the Kaka beak gall mite have been recorded. Two are predatory mites and one is a sucking bug, Ausejanus albisignatus (Hemiptera: Miridae).

Table: Predators of Kaka beak gall mite, Aceria clianthi (Acari: Prostigmata: Eriophyidae), from Plant-SyNZ database (11 November 2018). The reliability index shows the quality of evidence for the host association (0-10, 10=high quality).

Scientific Name	Common Name	Classification	Enemy Type	Reliability Index	Biostatus
Agistemus collyerae Gonzalez-Rodriguez, 1963	(Mite)	Acari: Prostigmata: Stigmaeidae	predator	9	adventive
Ausejanus albisignatus (Knight, 1938)	(Sucking bug)	Hemiptera: Miridae	predator	9	native
Typhlodromus caudiglans (Schuster, 1959)	(Mite)	Acari: Mesostigmata: Phytoseiidae	predator	10	adventive

The Kaka beak gall mite is found on its two endemic host plants and one naturalised plant from the same family. The mites on Birdsfoot trefoil, Lotus corniculatus, were found near where Kaka beak plants had recently been growing.

Kaka beak gall mites have pointed mouth parts that puncture the surface cells of young leaves. The plant responds to their feeding producing distortion of leaves and flower buds. Feeding on enlarging leaflets may just result in the folding over of the edge, while feeding on very young growths causes major distortion and stimulates the formation of more buds and young growths. This compact kind of growth is commonly called a witch's broom that is named after fungal induced galls on British birch trees.

Table: Host plants of the Kaka beak gall mite, Aceria clianthi (Acari: Prostigmata: Eriophyidae) from Plant-SyNZ database (11 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
Large Kaka beak	Clianthus maximus Colenso	Leguminosae	10	endemic
Kaka beak, Lobster claw, Parrot's beak, Kōwhai-ngutu-kākā	Clianthus punicens (G.Don) Sol. Ex Lindl.	Leguminosae	10	endemic
Birdsfoot trefoil	Lotus corniculatus L.	Leguminosae	10	naturalised

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.