Austrotephritis cassinae (Malloch, 1931)
Cassinia tephritid fly
Tephritis cassinae Malloch, 1931
Biostatus and distribution
This endemic gall fly is found throughout the country where there are coastal sand dunes and dry hill side soils with its host plant, Cottonwood/ Tauhinui, Ozothamnus leptophyllus (Compositae). The fly induces terminal bud galls in which a larva lives.
Conservation status: Found associated with its host plant, Cottonwood/ Tauhinui growing on coastal sand dunes and dry hill side soils.
Life stages and annual cycle
The fly appears to have only one generation per year with adults being present in the summer. The fly larvae induce terminal bud galls in its host plant Cottonwood/ Tauhinui, Ozothamnus leptophyllus (Compositae).
The body of adult flies is a dull golden brown and about 4.5 mm long. The wings are about 4.5 mm long, with pale areas and spots. Like all flies they have 1 pair of wings. The hind pair of wings is reduced to small knobs, halteres, that help the fly balance during flight. The wings and the 3 pairs of legs are attached to the middle section of the body, thorax. The head has two large compound eyes and a pair of antennae each baring a long bristle. The mouth is on the underside. The male has a rounded genitalia at the end of its abdomen, while the female has a slender end containing an ovipositor. The ovipositor is used to insert its eggs into terminal buds of its host plant. Only one egg is laid per bud.
Like other tephritid flies, it has a distinctive way of moving and fluttering its wings. At rest, the wings may be held together over the body or form a V.
When the larva hatches from the egg, it presumably burrows between the tiny leaves forming the terminal bud. The pale brown larva is legless and has black jaws for scraping plant tissue into its mouth. The larva moults as it gets larger. There are probably three larval stages, instars. A fully grown the larva is about 5 mm long. Larger larvae form a hollow in the centre of the bud. When fully grown, the larva makes a thin area between the leaves at the top of the bud. It then changes into a pupa inside its larval skin, which turns brown and is now called a puparium.
When the adult is ready to emerge, part of the head, just above the antennae, balloons out. This structure, the ptilinum, pushes the front of the pupa open. There is a line of weakness between the top and bottom halves of the first segments of the puparium that splits allowing the top and bottom to open up. During emergence the fly pushes an opening at the tip of the terminal bud gall. After the fly has crawled out, the ptilinum retracts into the head, the wings expand and the body hardens. Over the next 12 hours the fly acquires its full body colour.
It is not known how the male and females of this species find each other for mating.
The larva has a toothed, black mandible that it moves up and down to scrape the tissue on the inside of the gall or the tiny leaves in the terminal bud.
Adult flies may feed on nectar and pollen of flowers.
Adult flies can be recognised as Tephritidae by their shape and distinctive way of fluttering their wings when on plants. This group of flies require specialist skills for their identification. However, Cassinia tephritid fly, Austrotephritis cassinae is the only insect inducing terminal bud galls on its host plant Cottonwood/ Tauhinui, Ozothamnus leptophyllus (Compositae). The galls enable the presence of the flies to be detected and for adults to be reared from galls in late spring-early summer.
No natural enemies of the Cassinia tephritid fly are known.
It is likely that the fly larvae are hosts of parasitoid wasps and that adult flies preyed upon by birds, spiders, and other insects.
The Cassinia tephitid fly has been reared from galls on Cottonwood/ Tauhinui, Ozothamnus leptophyllus (G.Forst.) Breitw. & J.M.Ward (Compositae). The host plant is very variable and was at one time divided into several species in the genus Cassinia. Hence the flies common name. The plants live on Coastal Dunes and dry hill sides throughout New Zealand.
The galls are induced in shoot tips or terminal buds. The form of the gall is variable as is its host plant.
The larva has a toothed black mandible that it moves up and down to scrape the tissue on the inside of the gall. It is presumed that their feeding and a chemical released by the larva induce the plant to form the gall.
Hancock DL, Drew RAI 2003. A new genus and new species, combinations and records of Tephritinae (Diptera: Tephritidae) from Australia, New Zealand and the South Pacific. Australian Entomologist 30(4): 141-158.
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/
The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs.