INTERESTING INSECTS

By N A Martin (2017)

Hutton’s flower fly, Nikau palm flower fly

Oscinosoma huttoni Malloch, 1931

Caviceps huttoni (Malloch, 1931)

This endemic fly is found throughout New Zealand. The adult flies are associated with flowers and are often abundant on flowers of nikau palm Rhopalostylis sapida (Palmae). The larvae live in decaying leaves.

Conservation status: Widespread in parks and gardens as well as native habitats, not threatened.

Adult flies are found in flowers in spring, summer and autumn. They feed in the flowers. They are especially abundant on male flowers of Nikau palms Rhopalostylis sapida (Palmae) and presumably feed on pollen as well as nectar. Males and females mate on the flowers. There are probably several generations per year. Larvae live in decaying leaves.

Adult fly

The adult flies are small, about 2.0-2.5 mm long, much smaller than vinegar flies, Drosophila, that are seen around rotting fruit. The flies are yellow-brown with three darker brown stripes on the thorax (middle part of the body) and darker bands on some abdominal segments. The intensity and width of the dark brown stripes and bands varies greatly. Like all adult flies they have three pairs of legs and one pair of wings. The hind pair of wings is reduced to two small knobs, or halteres, which help the fly to balance during flight. The male has a rounded end of the abdomen, while the female has a slender end containing an ovipositor which is presumably used to insert eggs into decaying leaves.

Larvae and Pupae

The white larvae feed on decaying leaves. When fully grown, the larva pupates inside its larval skin, which turns brown and hard. This structure is called a puparium.

Female Hutton’s flower fly, Aphanotrigonum huttoni (Diptera: Chloropidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2GVZ]

Underside of a female Hutton’s flower fly, Aphanotrigonum huttoni (Diptera: Chloropidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2GW4]

Underside of a male Hutton’s flower fly, Aphanotrigonum huttoni (Diptera: Chloropidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2GW6]

Male Hutton’s flower fly, Aphanotrigonum huttoni (Diptera: Chloropidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2GW3]

Adult Hutton’s flower fly, Aphanotrigonum huttoni (Diptera: Chloropidae), museum specimen. Creator: Nicholas A. Martin. © Landcare Research. [Image: 2GVW]

Adult Hutton’s flower fly, Aphanotrigonum huttoni (Diptera: Chloropidae), museum specimen. Creator: Nicholas A. Martin. © Landcare Research. [Image: 2GVX]

A pair of mating Hutton’s flower flies, Aphanotrigonum huttoni (Diptera: Chloropidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2GW5]

White larva and three pupae of Hutton’s flower fly, Aphanotrigonum huttoni (Diptera: Chloropidae), and a fly larva. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2GW7]

Pupa of Hutton’s flower fly, Aphanotrigonum huttoni (Diptera: Chloropidae), with adult fly visible. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2GW8]

Empty pupal case of Hutton’s flower fly, Aphanotrigonum huttoni (Diptera: Chloropidae), after fly has emerged. Creator: Nicholas A. Martin. © Landcare Research. [Image: 2GVY]

These small yellow and brown flies require expert knowledge for identification. However, adults of this species can be easily recognised on flowers by their small size and yellow-brown colour and the three dark brown stripes on the thorax (middle section of the body).

White fly larvae on decaying leaves need to be reared so that the adults can be identified.

Female Hutton’s flower fly, Aphanotrigonum huttoni (Diptera: Chloropidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2GVZ]

Underside of a female Hutton’s flower fly, Aphanotrigonum huttoni (Diptera: Chloropidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2GW0]

Underside of a male Hutton’s flower fly, Aphanotrigonum huttoni (Diptera: Chloropidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2GW2]

Adult male Hutton’s flower fly, Aphanotrigonum huttoni (Diptera: Chloropidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2GWA]

Adult male Hutton’s flower fly, Aphanotrigonum huttoni (Diptera: Chloropidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2GW9]

Predators

One bird has been recorded feeding on adult flies. There are no reports of predators of the flies, but it is likely that they are preyed upon by birds, spiders and predatory insects.

Parasitoids

One larval-pupal parasitoid was found in pupae in dead leaves of New Zealand climbing spinach, Tetragonia implexicoma (Aizoaceae). Adult female wasps of Asobara albiclava (Hymenoptera: Braconidae), lay eggs in fly larvae associated with decaying leaves. The parasitoid larva kills the fly after it has pupated.

Four pupae of Hutton’s flower fly, Aphanotrigonum huttoni (Diptera: Chloropidae), the one on the left contains a parasitoid larva (Hymenoptera). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2GWB]

Pupa of Hutton’s flower fly, Aphanotrigonum huttoni (Diptera: Chloropidae), a parasitoid larva (Hymenoptera). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2GVS]

Adult Asobara albiclava Berry, 2007, (Hymenoptera: Braconidae) emerged from pupa of Hutton’s flower fly, Aphanotrigonum huttoni (Diptera: Chloropidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2GVT]

Adult Asobara albiclava Berry, 2007, (Hymenoptera: Braconidae) emerged from pupa of Hutton’s flower fly, Aphanotrigonum huttoni (Diptera: Chloropidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2GVV]

Underside of adult female Asobara albiclava Berry, 2007, (Hymenoptera: Braconidae) emerged from pupa of Hutton’s flower fly, Aphanotrigonum huttoni (Diptera: Chloropidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2GVU]

Adults of this species of fly are found on flowers where they feed and mate. Large numbers are found on some species of flower. In Auckland, they are especially abundant on nikau palm, Rhopalostylis sapida (Palmae). They appear to feed on both nectar and pollen.

The fly larvae live in decaying plants. Adult flies have been reared from larvae in decaying leaves of New Zealand climbing spinach, Tetragonia implexicoma (Aizoaceae) and New Zealand celery, Apium prostratum (Umbelliferae).

Research project: Where are the larvae of Hutton’s flower fly

Large numbers of adult flies on favoured flowers indicate that the flies are breeding somewhere nearby. It is easy to collect and keep adult flies. Adult flies have been reared from decaying leaves of two plants. What are the other plants on which they live? It would be possible to test a variety of substrates for their suitability for egg laying and for their ability to support larval development.

Harrison RA. 1959. Acalypterate Diptera of New Zealand. N.Z. Department of Scientific and Industrial Research Bulletin. 128: 1-382.

Plant-SyNZ: Invertebrate herbivore-host plant association database. plant-synz.landcareresearch.co.nz/.

Spencer KA. 1977. A revision of New Zealand Chloropidae. Journal of the Royal Society of New Zealand. 7 (4): 433-472.

The 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.