INTERESTING INSECTS

By N A Martin (2017)

Galium gall mite

The Gallium gal mite, Cecidophyes rouhollahi (Acari: Eriophyidae) is an adventive species from Europe and was first found in New Zealand in June 2017. It is widespread in Auckland. Its host plant is the adventive weed, Cleaves or Goose grass, Cleavers, Galium aparine (Rubiaceae). The mite induces the leaf edges to roll inwards and the leaves to curl.

Conservation status: At present only known in the Auckland Region on an adventive weed.

This gall mite is very tiny. Adult mites are about 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, this induces the edges to roll inwards. 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 Galium gall mite, Cecidophyes rouhollahi 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 in New Zealand known to induce leaf galls on Cleaves, Galium aparine (Rubiaceae). Mites feeding on the young expanding leaves induces the edges to roll inwards and the leaf to curl. Sometimes just the terminal leaves are affected, while on other plants, most leaves are affected.

In Northern Hemisphere this Galium gall mite, Cecidophyes rouhollahi can live on three species of Galium. The leaf gall induced by the mite is identical to that caused by another species of mite in the same mite genus.

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

The only known host plant in New Zealand of the Galium gall mite, Cecidophyes rouhollahi, is the adventive species Galium aparine (Rubiaceae), also known as Cleaves and Goose grass. The mites feeding on the young expanding leaves induces the edges to roll inwards and leaves to curl. Sometimes just the terminal leaves are affected, while on other plants, most leaves are affected.

A new species of Cecidophyes (Acari: Eriophyidae) from Galium aparine (Rubiaceae) with notes on its biology and potential as a biological control agent for Galium spurium. Craemer C, Sobhian R, McClay SR, Amrine Jr. JW. 1999. International Journal of Acarology, 1999, 25 (4): 255-263.

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

Qing Hai Fan, MPI, for photographs of slide mounted mites.