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8 Nicholas Martin
Drosophilidae) and the evolution of leaf mining.
Nicholas Martin*
15 Rutland Road, Mt. Wellington, Auckland 1051
Email: [email protected]
Fly larvae forming mines in New Zealand celery, Apium prostratum
(Apiaceae) were reared and identified as Scaptomyza (Bunostoma) flavella.
A laboratory colony was established and it was found that first instar
larvae did not burrow into leaves, though later instars did. All larval instars
could live and grow in decaying celery leaves. This fly species is a
facultative leafminer. Other species of the subgenus in New Zealand are
either decaying vegetation feeders or true leaf miners.
The story so far
I reported the discovery in 2011 of the New Zealand spinach leafminer,
Scaptomyza (Bunostoma) sp. (Diptera: Drosophilidae) at Piha and
Karekare, west Auckland breeding on Tetragonia implexicoma (Miq.)
Hook.f. (Aizoaceae) (Martin 2012). This proved to be an undescribed
species previously collected from the Chatham Islands; a strange
distribution, Chatham Islands and west coast of Auckland. A second
undescribed species, discovered by Brenda May in 1982, is a leafminer on
Pratia (= Lobelia) angulata G.Forst. (Campanulaceae). There are two
described species: S. (B.) fuscitarsis Harrison, 1959, which is common in
grasslands south of Auckland and whose larvae feed on decaying plants,
and S. (B.) flavella Harrison, 1959, which is found around the coast and on
offshore islands.
The discovery of S, flavella larvae
On 15 November 2013 there was an exceptionally low tide at Muriwai,
West Auckland. I walked along the beach of south of Maori Bay to view
the pillow lava in the cliffs. On the way back I examined the vegetation at
The Weta 47: 8-11
the base of the cliffs and found New Zealand celery, Apium prostratum
Labill. ex Vent. (Apiaceae), growing under trees in the spray zone. One
group of plants had leaf mines that appeared to contain fly larvae. I
collected many leaves. Viewed with transmitted light under a stereomicroscope they looked like Scaptomyza larvae. The coastal distribution of
the plant pointed to them being S. flavella, which is what they proved to
Figure 1. Leaf of New Zealand celery, Apium prostratum (Apiaceae) with
mines made by larvae of Scaptomyza (Bunostoma) flavella
(Drosophilidae); arrow points to larva in leaf (photographer Tim Holmes,
copyright Plant & Food Research).
10 Nicholas Martin
A third species of native Scaptomyza that is a leaf miner: end of story? No
such luck!
Rearing S. flavella
Early in the spring I had improved my technique for rearing the New
Zealand spinach leafminer, by supplying the newly emerged adult flies
with dilute honey solution, and had succeeded in getting them to lay eggs
on leaves. I observed the first instar larvae burrow into leaves
demonstrating that it is a true leaf miner. Using the same approach I
released S. flavella adults into a small cage with honey solution and celery
leaves standing in water with tissue around the leaf stalks to prevent access
to the water. Some leaves were damaged by caterpillars, Merophyas sp.
(Lepidoptera: Tortricidae) that can tunnel into leaves, a common
occurrence, I found, in summer. Eventually the flies laid eggs on celery
leaves and larvae were seen burrowing through the leaves. I tried putting
first instar larvae on intact and undamaged leaves, but they did not burrow
in, whereas older larvae put on intact leaves, rasped the leaf surface and
they created tunnels in the leaves forming large blotch mines.
Figure 2. Adult Scaptomyza (Bunostoma) flavella (Drosophilidae) reared
from larvae living in live leaves of New Zealand celery, Apium prostratum
(Umbelliferae) (photographer Tim Holmes, copyright Plant & Food
The Weta 47: 8-11
It appears we have a fly species that is a facultative leafminer. Indeed it
can be reared entirely on decayed celery leaves. The larger larvae will also
burrow into Chenopodium sp. (Amaranthaceae) leaves though my
impression is that burrowing is not as extensive.
Flies in several families have larvae that are leaf miners (Hering 1951).
There has been speculation about the evolution of the leaf mining habit.
Within the genus Scaptomyza members of the subgenus Scaptomyza are
leaf miners and because of the detailed information on the genetics of
Drosophila species, the origin of leaf mining in S. (S.) flava (Fallen, 1823)
was studied. It is estimated that leaf mining evolved between 6 and 16
million years ago (Whiteman et al. 2012). They also identified some of the
genetic changes involved. It is remarkable that in New Zealand that we
have two species of the subgenus Bunostoma that are leafminers, one
species that appears only to feed on decaying plants and a fourth species
that is a facultative leafminer. What a great research topic for someone!
Frances MacDonald for care of the New Zealand spinach and New
Zealand celery plants.
Hering EM. 1951. Biology of leaf miners. Uitgeverij Dr W. Junk,‘s
Gravenhage, The Netherlands. 420 p.
Martin NA. 2012. Tales of two discoveries. The Weta 44: 13-19.
Whiteman NK, Gloss AD, Sackton TB, Groen SC, Humphrey PT, Lapoint
RT, Sonderby IE, Halkier BA, Kocks C, Ausubel FM and others. 2012.
Genes Involved in the Evolution of Herbivory by a Leaf-Mining,
Drosophilid Fly. Genome Biology and Evolution 4(9): 900-916.