INTERESTING INSECTS

By N A Martin (2017)

Haloragis gall mite, Toatoa bud gall mite

This endemic gall mite was first found in 1956 in bud galls on its host plant, Toatoa/Shrubby haloragis, Haloragis erecta (Haloragaceae). In 1956 and 1957 bud galls were found in Hawkes Bay, Rotorua, Wellington and North Canterbury. The galls and mites were not seen again until they were rediscovered in October 2012 at Whatipu on the west coast of Auckland. During the next 12 months the mite was found in several other places in the Auckland Region.

Conservation status: Probably widespread, but uncommon.

This gall mite is very tiny. Adult mites are about 0.15-0.19 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 buds, the surfaces of bud structures develop hairs and a red colour. Also the structure of the bud become thickened. The mites shelter, feed and breed between the structures of 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 flower buds, 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 red flower bud galls on stems of Toatoa/Shrubby haloragis, Haloragis erecta (Haloragaceae). Flower bud galls on other plants are caused by other mite or insect species.

Flowers on Toatoa/Shrubby haloragis are usually green. Sometimes plants have red flowers without any signs of gall tissue.

Yellow predatory mites (Stigmaidae) were found on galls in an Auckland Regional Park. Other kinds predatory mites and insects may feed on these gall mites.

Haloragis gall mite, Aceria victoriae (Acari: Eriophyidae) is only known to live on Toatoa/Shrubby haloragis, Haloragis erecta (Haloragaceae). Mites feeding on flower buds induce red galls on flowering shoots. Flowers on Toatoa/Shrubby haloragis are usually green. Sometimes plants have red flowers without any signs of gall tissue.

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.

Ramsay GW. 1958. A new species of gall-mite (Acarina: Eriophyidae) and an account of its lifecycle. Transactions of the Royal Society of New Zealand. 85 (3): 459-464.

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