INTERESTING INSECTS

By N A Martin (2017)

Nikau palm gall mite

This endemic gall mite has been found in the North and South Islands of New Zealand on its primary host plant, nikau palm, Rhopalostylis sapida (Palmae). It is found in parks and gardens as well as in native ecosystems.

Conservation status: It is common on its host plant in parks and gardens as well as in native ecosystems.

This gall mite is very tiny. Adult mites are 0.212 - 0.238 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 that also looks like a small adult. The last juvenile stage moults into an adult mite. There are male and females. The larger mites become covered in white flocculent wax. The mite lives in dense colonies on the underside of palm fronds. It appears that in older colonies they lay eggs on the brown dead leaf tissue and move to the dead tissue to moult.

Feeding

The mites have pointed mouth parts that puncture the surface cells on the underside of palm fronds. They suck up the cell sap. During feeding, the mites may inject saliva into the plant. The leaf tissue on which the mites are feeding turns yellow then becomes dark brown. In young colonies they are mainly on green leaf tissue. In older colonies, the mites are found on and around the dark brown area of the leaf. This gives the impression that they are feeding on dead leaf tissue, but it is unlikely that they can feed on the dead plant cells. Though, maybe they can feed on fungal hyphae as well as plant cells.

Walking

The mite uses its legs for walking, but can also hold on to the plant with the tip of its rear end which acts as a sucker.

Dispersal to new palm fronds and new plants

The mite can form new colonies on other parts of the same palm leaf. It is presumed some female mites walk from old colonies to elsewhere on the same leaf. Mites also colonise young mature palm leaves of the same plant. Female mites probably also walk to these younger leaves. 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, the distinctive white mites covered in white flocculent wax in association with dark brown areas on the underside of nikau palm fronds enable the Nikau palm gall mite to be recognised. Even if the mites are absent, white moulted skins on the on the dark brown patches also enable the presence of the mite to be detected. A magnifying glass such as a 10 times lens, may be useful when looking for these mites.

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

The Nikau palm gall mite, Nameriophyes sapidae (Acari: Eriophyidae) lives on its primary host plant, nikau palm, Rhopalostylis sapida (Palmae). It has also been found on cultivated Kermadec Island palm, Rhopalostylis baueri, grown outdoors in Auckland.

Feeding

The mites have pointed mouth parts that puncture the surface cells on the underside of palm fronds. They suck up the cell sap. During feeding, the mites may inject saliva into the plant. The leaf tissue on which the mites are feeding turns yellow then becomes dark brown. In young colonies they are mainly on green leaf tissue. In older colonies, the mites are found on and around the dark brown area of the leaf. This gives the impression that they are feeding on dead leaf tissue, but it is unlikely that they can feed on the dead plant cells. Though, maybe they can feed on fungal hyphae as well as plant cells.

Table: Host plants of the Nikau palm gall mite, Nameriophyes sapidae (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
Kermadec Island palm, Kermadec Island nikau	Rhopalostylis baueri (Seem.) H.Wendl. & Drude	Palmae	10	indigenous, non-endemic
Feather duster palm, Nikau palm, Nīkau	Rhopalostylis sapida H.Wendl. & Drude	Palmae	10	endemic

Eriophyid gall mites belong to the superfamily Eryiophyoidea. These mites have several unusual features. For example, though most mites have four pairs of legs like spiders, Eriophyoidea 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.

Martin NA, Zhang Z-Q. 2011. Extended distribution and host plants of Nameriophyes sapidae Xue & Zhang 2008 (Acari: Eriophyidae) in New Zealand. Zootaxa. 2796: 67-68.

Xue X-F, Zhang Z-Q. 2008. New Zealand Eriophyoidea (Acari: Prostigmata): an update with descriptions of one new Genus and 6 new species. Zootaxa. 1962: 1-32.

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

Landcare Research New Zealand Limited (Landcare Research) for permission to use photographs.

Magnolia Press for permission to reproduce figures of Nameriophyes sapidae Xue & Zhang 2008.