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Tales of two discoveries

Nicholas Martin* 15 Rutland Road, Mt. Wellington, Auckland 1051 Email:[email protected] *Research Associate, Landcare Research

Abstract Previously unknown species of insect continue to be discovered, even in the heart of our largest city, Auckland. Events leading to the discovery of the Loxsoma whitefly (Trialeurodes sp. (Hemiptera: Aleyrodidae)) and the New Zealand Spinach leaf miner (Scaptomyza (Bunostoma) sp. (Diptera: Drosophilidae)) are described. The significance of these discoveries is discussed. Loxsoma whitefly In July 2012, Dr Robert Hoare, lepidopterist at Landcare Research visited Chatswood Reserve, Birkenhead, on Auckland’s North Shore. Searching on the undersides of fronds of the fern, Loxsoma cunninghamii, in the forlorn hope of spore-feeding Lepidoptera larvae, he found instead numerous whitefly larvae (Hemiptera: Aleyrodidae). Loxsoma cunninghamii is a rare fern, only found North of the Waitemata Harbour, on Little Barrier Island and Coromandel Peninsula. He showed the whiteflies to colleagues, Rosa Henderson and Nicholas Martin, who realized that they were of a previously unknown species, one of more than 10 undescribed species of fern whitefly in New Zealand.

There is only one named fern whitefly in New Zealand: the shining spleenwort whitefly,Trialeurodes asplenii, described in 1890. It is commonly seen on the underside of the fronds of its main host plant, Asplenium oblongifolium (Aspleniaceae). Rosa Henderson and I have been collecting information about whitefly on ferns for several years. We recently realized that many of the whitefly that occur on other species of fern and that look superficially similar to the shining spleenwort whitefly, are in fact undescribed species in the genus Trialeurodes. It appears that most of these whitefly species are monophagous, i.e. they live only on one species of fern. For example the hound’s tongue fern whitefly only lives on Microsorum pustulatum (Polypodiaceae). This whitefly is rare in Auckland, 14 Nicholas Martin but common in Dunedin. The sickle spleenwort whitefly, which is found on Asplenium polyodon, is known from only three reserves on the southern fringe of suburban Auckland. In contrast the umbrella fern whitefly is found on most patches of its host, Sticherus cunninghamii (Gleicheniaceae).

Adults of all New Zealand fern whitefly (Fig.1.A.) are very similar and show few or no morphological characters that allow them to be distinguished. Fortunately the scale-like larvae (Fig. 1.B) have distinctive features that can be seen with a lens or magnifying glass. The Loxsoma fern whitefly larvae are unpigmented and surrounded by a neat long fringe of white wax filaments. The larvae are spaced out on the underside of the fern frond, whereas other species with a prominent white wax fringe, such as the shining spleenwort whitefly, usually have larvae that are clumped together, forming a messy area of white wax. The wax filaments of the shining spleenwort whitefly are thinner and longer than those of the Loxsoma whitefly. Other species such as the hound’s tongue whitefly have pigmented larvae. Whitefly are known from about fifteen species of fern, including Adiantum cunninghamii, Asplenium oblongifolium, A. polyodon, Blechnum colensoi, Dicksonia lanata, Dicksonia squarrosa, Hymenophyllum sp. Lastreopsis hispida, Loxsoma cunninghamii, Microsorum pustulatum, Paesia scaberula, Pneumatopteris pennigera, Polystichum vestitum, and Sticherus cunninghamii. It is not certain how many of these fern living whitefly are distinct species. The taxonomy of this group would make an excellent research project for a student or other enthusiast.

New Zealand spinach leafminer For over six hundred years New Zealand spinach leafminer flies have managed to keep their existence secret from humans. All this changed when in 2012, during late winter, a female fly laid eggs in leaves of New Zealand spinach plants (Tetragonia sp (Aizoaceae)) near a west coast Auckland beach.

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Some weeks later, in early September, an entomologist walked along the beach towards one of his favorite tracks up through the forest of the Waitakere Ranges. As he approached the base of the track, he spotted some brown blotches on the leaves of the aforementioned spinach plant (Fig.2.). He picked one leaf, held it up to the light and looked at it through his magnifying glass. He could see that the brown blotch was a leaf mine, not a rotten part of the leaf. And he had never before seen a leaf mine like this on New Zealand spinach. He carefully collected some more mined leaves into a self-sealing plastic bag.

Next day he examined the leaves with a microscope, using transmitted light. He could see that the leaf-miners were fly larvae and that they did not belong to the family Agromyzidae a group that contains many such miners. Some larvae had already pupated in the leaf. Now it was just a matter of waiting until the adults emerged. What would they be?

Two weeks later, adult flies had emerged in some of the containers holding the leaves. A close examination of the wings and head of one specimen revealed that it belonged to the family Drosophilidae. This family includes the vinegar flies (Drosophila species) made famous by their use for genetic studies last century. The dorsal area of the thorax between the wings had only two rows of acrostichal setae (tiny setae along the mid line). This fly was of a previously unknown species in the genus Scaptomyza (Fig.3.)

Scaptomyza is a large genus of flies with a worldwide distribution. The New Zealand spinach leafminer belongs to a small group of flies in the subgenus Bunostoma that are found on Pacific Islands and in Australia and New Zealand. New Zealand is now known to have five species in this subgenus, making the country a relative Bunostoma hotspot!

I started a study of these flies several years ago and in my retirement I am planning to produce a paper on the genus Scaptomyza in New Zealand. In addition to the five endemic species in the subgenus Bunostoma, there are two adventive species, Scaptomyza (Parascaptomyza) elmoi Takada, 1970 and Scaptomyza (Scaptomyza) flava (Fallen, 1823). The larvae of the former feed on decaying plants, while the latter is a leafminer of brassicas 16 Nicholas Martin and plants in several other families (Martin 2004). Two of the endemic species have been named: Scaptomyza (Bunostoma) flavella Harrison, 1959 and Scaptomyza (Bunostoma) fuscitarsis Harrison, 1959. The former is found around the coast and on offshore islands, while the latter is common in grasslands South of Auckland. Its larvae feed on decaying plants. One of the three unnamed species is found on the Chatham Islands and appears to be closely related to S. flavella. The other two species are both leaf miners. The Pratia leafminer was discovered in Huia and reared by Brenda May in 1982. It has since been found in several places in the Waitakere Ranges, on Mount Taranaki and in the South Island. This species appears closely related to S. fuscitarsis. The New Zealand spinach leafminer has now been found in two places on the west coast of the Waitakere Ranges. Each site was in the shade, and not an obvious place to look for leaf mines of flies. Thank goodness that female fly chose to lay its eggs so close to a favourite track!

Discussion The discoveries of the Loxsoma whitefly and New Zealand spinach leafminer were chance finds that depended upon natural historians being in the right place at the right time. Having high quality native ecosystems that are easily accessible has been an important factor in the discovery of these and other species of invertebrates in Auckland, as elsewhere in New Zealand. In addition to its Regional Parks and Department of Conservation Reserves, Auckland is fortunate to have many urban reserves of native forest and other plant communities. These discoveries demonstrate the value of these reserves in conserving native biodiversity. Who knows what other undiscovered species are on our doorstep?

Acknowledgement Robert Hoare for helpful suggestions.

References Martin NA 2004. History of an invader, Scaptomyza flava (Fallen, 1823) (Diptera: Drosophilidae). New Zealand Journal of Zoology. 31 (1): 27-32

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A

B

Fig. 1.A. Loxsoma whitefly larva (Trialeurodes sp. (Hemiptera: Aleyrodidae)); B. Loxsoma whitefly adult (Trialeurodes sp. (Hemiptera: Aleyrodidae)) 18 Nicholas Martin

Fig.2. New Zealand spinach (Tetragonia sp. (Aizoaceae)) with blotch mine made by Scaptomyza (Bunostoma) sp. (Diptera: Drosophilidae)).

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Fig.3. Adult Scaptomyza (Bunostoma) sp. (Diptera: Drosophilidae)) reared from larva in a blotch mine in New Zealand spinach (Tetragonia sp. (Aizoaceae))