Senecio gall fly - Sphenella fascigera
By N A Martin (2015)
Biostatus and Distribution
This endemic gall fly is found throughout the country in open ground and forests. The fly larvae either live in the flowers or induce stem galls in its host plants, herbaceous Senecio species and the shrub Brachyglottis kirkii.
Conservation status: Widespread in native ecosystems and present in gardens, parks, and waste ground.
Life Stages and Annual Cycle
The fly breeds all year in Auckland where suitable host plants are available. In colder regions it may overwinter as adults. The fly induces stem galls in host plants with small flowers, e.g., Senecio glomeratus, or breeds in the larger flowers of other host plants, e.g., Senecio lautus.
The body of adult flies is a dull golden brown and about 4 mm long. The wings are about 3.75 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 make holes in stems or flower buds into which eggs are laid.
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 bores into the flower or plant stem. The white 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. When fully grown, the larva makes a thin area in the wall of the gall or flower and 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 through the thin ‘window’ in the gall or flower. 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 ovaries and developing seeds in a flower.
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. Senecio gall fly, Sphenella fascigera, belong to a group of flies with 2 pairs of seta, bristles, on the scutellum, upper side of the last thorax segment. Examination with a microscope is required to distinguish the species of this group.
The presence of Senecio gall flies can be recognised by their damage to flowers and the galls they induce in host plants. Plants with damaged flowers include Brachyglottis kirkii, Senecio lautus and Senecio vulgaris. Flower buds may have black areas, ‘windows’ and exit holes. Flowers may also be blackened and have dead florets. Seed feeding may be seen on opening flowers. Some damaged flowers should have within them a white larva or black pupa.
Galls are induced in stems, especially in the area where they branch. Often the stem and branches are distorted.
An unnamed wasp parasitoid (Hymenotpera) has occasionally been reared from juveniles of this tephritid gall fly. One wasp, Podagritus albipes (Hymenoptera: Crabronidae), has been recorded catching adult senecio gall flies. Adult flies are also likely to be preyed upon by birds, spiders, and other insects.
|Scientific Name||Common Name||Classification||Enemy Type||Reliability|
|Podagritus albipes (Smith, 1878)||(Wasp)||Hymenoptera: Crabronidae||predator||10||endemic|
The Senecio gall fly, Sphenella fascigera, is associated with Compositae (daisy family). Larvae live in flowers of Brachyglottis kirkii and Senecio species with large flowers, such as S. lautus and S. vulgaris. They also induce galls in stems of Senecio species that have small flowers, and in ragwort, Jacobaea vulgaris.
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. In flowers they feed on the ovaries and developing seeds.
|Common Name(s)||Scientific Name||Family||Reliability Index||Biostatus|
|Forest tree groundsel, Kirk's daisy, Kohuhurangi, Kohukohurangi, Kohurangi, Kokohurangi, Ororo, Tapairu||Brachyglottis kirkii (Kirk) C.J.Webb||Compositae||10||endemic|
|Ragwort, Saint James' wort, Tansy ragwort||Jacobaea vulgaris Gaertn.||Compositae||10||naturalised|
|Australian fireweed||Senecio bipinnatisectus Belcher||Compositae||10||naturalised|
|Fireweed||Senecio diaschides D.G.Drury||Compositae||10||naturalised|
|Senecio esleri C.J.Webb||Compositae||10||naturalised|
|Fireweed, Pukatea||Senecio glomeratus Poir.||Compositae||10||non-endemic|
|Fireweed||Senecio hispidulus A.Rich.||Compositae||10||non-endemic|
|Fireweed, Shore groundsel, Variable groundsel||Senecio lautus G.Forst. ex Willd.||Compositae||10||non-endemic|
|Australian burnweed, Australian fireweed, Fireweed||Senecio minimus Poir.||Compositae||10||non-endemic|
|Gravel groundsel||Senecio skirrhodon DC.||Compositae||10||naturalised|
|Common groundsel, Groundsel||Senecio vulgaris L.||Compositae||10||naturalised|
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.