8 Nicholas Martin Scaptomyza (Bunostoma) flavella (Diptera: Drosophilidae) and the evolution of leaf mining. Nicholas Martin* 15 Rutland Road, Mt. Wellington, Auckland 1051 Email: [email protected] Abstract 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 9 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 be. 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 Research). The Weta 47: 8-11 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. Discussion 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! Acknowledgement Frances MacDonald for care of the New Zealand spinach and New Zealand celery plants. References 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.
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