INTERESTING INSECTS

By N A Martin (2018)

Flax fungus beetle

At least six species of unnamed beetles in the genus Melanophthalma (Latridiidae) are present in New Zealand and are awaiting description and naming.

The endemic Flax fungus beetle is an undescribed species that has been found feeding and breeding on fungi on leaves of New Zealand flax in Auckland. Nothing is known about its distribution and abundance.

Conservation status: Present in the Auckland region, does not appear to be endangered.

In Auckland, all life stages of the Flax fungus beetle were found on underside of New Zealand flax, Phormium tenax (Hemerocallidaceae) with Flax Zasmidium leaf spot, Zasmidium dianellae (Ascomycota: Mycosphaerellaceae) July.

Adults are typical beetles, each with six legs and hard wing covers (elytra). They are small, about 2 mm long. They are brown with the head, antennae and legs being paler than the rest of the body and wing covers. Their wings, which are longer than the wing covers, are kept safely folded up under the wing covers, except when needed for flying.

After mating the females lay small oval eggs on the fungal growth on the underside of flax leaves. Tiny white sixed-legged larvae hatch from the eggs. They have brown heads and the body turns grey. The body is covered by tufts of setae (bristles). There are several larval instars (stages) when each instar is fully grown, moults (changes skin). During moulting the skin splits on the upper, dorsal, surface and the next instar larva pulls itself out. The fully grown larva moults into a pupa its larval skin stays at the base of the pupa. The pupa is white and has wing buds. When the adult has developed inside the pupa, it emerges and the elytra and wings expand and harden.

Feeding

Adults and larvae have chewing mouth parts. They feed on the fungal growths on the underside of flax leaves.

There are many kinds of small beetles in New Zealand. They can only be conclusively identified by an expert. It is not known if other beetles in the genus Melanophthalma or even the family Latridiidae feed on the Flax Zasmidium leaf spot fungus. However, if small beetle larvae, pupae and adults similar to those illustrated here are found on the underside of a flax leaf in a colony of the fungus, Flax Zasmidium leaf spot, they are likely to be a member of this family of beetles.

No natural enemies of the Flax fungus beetle were observed. Birds, spiders and predatory insects probably prey upon them.

The only known host of the Flax fungus beetle is the Zasmidium leaf spot fungus when it infests New Zealand flax. The adults and larvae feed by chewing the fungal growths on the underside of the leaves.

Table: Host plants of the Flax fungus beetle, Melanophthalma sp. 6 (Coleoptera: Latridiidae) from Plant-SyNZ database (18 April 2018). 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
Flax Zasmidium leaf spot	Zasmidium dianellae (Sawada & Katsuki) U. Braun	Mycosphaerellaceae	9	indigenous, non-endemic
Flax, Lowland flax, New Zealand flax, Swamp flax, Harakeke, Harareke, Kōrari	Phormium tenax J.R.Forst. & G.Forst.	Hemerocallidaceae	7	endemic

Specimens of Melanophthalma sp. 6 are deposited in the NZAC and labelled NAM1207C

Rich Leschen for helpful comments.

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