INTERESTING INSECTS

By N A Martin (2017)

Pohuehue pocket gall mite, Muehlenbeckia pocket gall mite

Aculus lambi (Manson, 1965)

Criotacus lambi (Manson, 1965)

This endemic gall mite has been found in the North and South Islands of New Zealand on its host plants, Muehlenbeckia species (Polygonaceae). Feeding by the mites may induce pocket galls on leaves.

Conservation status: Widespread, not threatened.

This gall mite is very tiny. Adult mites are about 0.2 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 the mites feed on young expanding leaves, leaf cells in the area multiply causing a thickening and expansion of the leaf, 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.

When mites first feed on a young leaf, several may do so along the edge of an unrolling leaf. This would result in a line of pocket galls, a feature seen on some leaves. On some plants the leaf edge just rolls over and mites live in the roll.

Some plants of one species of host plant, Muehlenbeckia australis, do not develop galls when leaves are fed on by this species of mite. This indicates genetic variation in the host plant and its reaction to chemicals in the saliva of the mite.

Dispersal to new stems and new plants

When the plant grows new leaves, female mites disperse to these and their feeding induces the formation of new galls. It is presumed mites walk from the old galls and 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 induce pocket galls on leaves of Muehlenbeckia species. Pocket galls on other plants are caused by other mite species.

Leaves of some plants of Muehlenbeckia australis, have rolled edges in which eriophyid mites are living. These may also be Eriophyes lambi.

Also on, Muehlenbeckia australis, large numbers of eriophyid mites may be seen on the underside of leaves. All specimens have been identified as Eriophyes lambi. Leaves of these plants do not develop galls. However, large numbers of free living eriophyid mites may also be seen on Muehlenbeckia complexa These mites are usually associated with distorted leaves and are an unnamed species.

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

Pohuehue gall mite, Eriophyes lambi (Acari: Eriophyidae), only lives on Muehlenbeckia species (Polypodiaceae). Mite feeding can induce pocket galls on leaves. The galls are often in straight lines, suggesting that mites were sheltering by the partly unrolled leaf when their feeding induced formation of galls.

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 the mites feed on young expanding leaves, leaf cells in the area multiply causing a thickening and expansion of the leaf, 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. When mites first feed on a young leaf, several may do so along the edge of an unrolling leaf. This would result in a line of pocket galls, a feature seen on some leaves. On some plants the leaf edge just rolls over and mites live in the roll.

Some plants of one species of host plant, Muehlenbeckia australis, do not develop galls when leaves are fed on by this species of mite. This indicates genetic variation in the host plant and its reaction to chemicals in the saliva of the mite.

Table: Host plants of the Pohuehue pocket gall mite, Eriophyes lambi (Acari: Prostigmata: Eriophyidae) from Plant- SyNZ database (27 March 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
Large-leaved muehlenbeckia, Pōhuehue, Puka	Muehlenbeckia australis (G.Forst.) Meisn.	Polygonaceae	10	indigenous, non-endemic
Creeping muehlenbeckia, Creeping pohuehue, Pōhuehue	Muehlenbeckia axillaris (Hook.f.) Endl.	Polygonaceae	10	indigenous, non-endemic
Scrub pohuehue, Small-leaved pohuehue, Wire vine, Pōhue, Pōhuehue, Pōpōhue, Tororaro, Waekāhu	Muehlenbeckia complexa (A.Cunn.) Meissn.	Polygonaceae	10	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.

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.

Eric Scott for helpful suggestions.

Dr Z-Q Zhang and student for examination and identification of free living eriophyid mites on Muehlenbeckia species.

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