INTERESTING INSECTS

By N A Martin (2017)

Bindweed gall mite

Vasates calystegiae Lamb, 1952

This endemic gall mite has been found in the North and South Islands of New Zealand on its host plants, Calystegia species and Convolvulus arvensis. Feeding by the mite induces pocket galls on young leaves.

Conservation status: Widespread, not threatened.

This gall mite is very tiny. Adult mites are about 0.2-0.3 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 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 young expanding leaves, leaf cells in the area multiply causing a thickening and expansion of the leaf tissue, which forms an invagination. This expands to form a protuberance on the other side of the leaf. The sides of the invagination grow upwards and almost join, leaving a narrow opening to the gall. 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 leaves, adult female mites disperse to these and their feeding induces the formation of new galls. It is presumed 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 by plant damage symptoms. This mite species is the only one known to induce pocket galls on leaves of Calystegia species and Convolvulus arvensis in New Zealand. Pocket galls on other plants are caused by other mite or insect species.

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

Bindweed gall mite, Aceria calystegiae (Acari: Eriophyidae), lives on native and adventive plant species in the bindweed family, Convolvulaceae; Calystegia species and Convolvulus arvensis. Mite feeding on young leaves induces pocket galls. High numbers of mites on young leaves result in many galls and distorted leaves.

Table: Host plants of the Bindweed gall mite, Aceria calystegiae (Acari: Prostigmata: Eriophyidae) from Plant- SyNZ database (11 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
	Calystegia marginata R.Br.	Convolvulaceae	10	non-endemic
Greater bindweed, Pink bindweed, Hedge bindweed, Akapōhue, Nahinahi, Panahi, Panake, Pōhue, Pōhuehue, Pōhuhue, Pōpōhue, Rauparaha	Calystegia sepium (L.) R.Br.	Convolvulaceae	10	naturalised
Great bindweed, Greater bindweed	Calystegia silvatica (Kit.) Griseb.	Convolvulaceae	10	naturalised
Shore bindweed, Panahi, Paraha, Pōhue, Poue	Calystegia soldanella (L.) R.Br.	Convolvulaceae	10	non-endemic
Climbing convolvulus, New Zealand bindweed, Pōuwhiwhi, Pōwhiwhi, Rarotawake (edible roots)	Calystegia tuguriorum (G.Forst.) R.Br. ex Hook.f.	Convolvulaceae	10	non-endemic
Field bindweed	Convolvulus arvensis L.	Convolvulaceae	8	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.

This gall mite is named after a New Zealand scientist, Dr Kenneth Lamb, who studied gall forming mites and insects during the 1950s. He discovered many kinds of galls on native plants.

Lamb KP 1960. A check list of New Zealand Plant Galls (Zoocecidia). Transactions of the Royal Society of New Zealand 88(1): 121-139.

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.