FNZ 16 - Nepticulidae (Insecta: Lepidoptera) - Introduction
Donner, H; Wilkinson, C 1989. Nepticulidae (Insecta: Lepidoptera). Fauna of New Zealand 16, 92 pages.
(
ISSN 0111-5383 (print),
;
no.
16.
ISBN 0-477-02538-2 (print),
).
Published 28 Apr 1989
ZooBank: http://zoobank.org/References/9BE5D9B7-27E2-46F0-8A35-4D4912BA0D99
Introduction
New Zealand Lepidoptera whose larvae mine leaves or green stems for all or part of their larval life are found in ten families: Nepticulidae, Gracillariidae, Roeslerstammiidae, Yponomeutidae, Lyonetidae, Elachistidae, Momphidae, Gelechiidae, Tortricidae, and Pterophoridae.
The Nepticulidae of New Zealand all have larvae that mine leaves, feeding on the epidermal or mesophyll layer. While there is no hard-and-fast diagnostic character distinguishing nepticulid mines from others, New Zealand nepticulid mines are usually relatively short (under 30 mm) and increase in width at a more or less even rate. Mines of some species are shown in Fig. 19 - 28.
The Nepticulidae as a whole are monotrysian microlepidoptera which as larvae tunnel or mine in leaves, petioles, stems, fruits, and bark of plants; some even cause the production of galls. The family is a member of the Glossata: Myoglossata, and is more advanced than the Eriocraniidae (Dacnonypha) in having, for example, intrinsic musculature in the haustellum. The Nepticulidae and Opostegidae are currently regarded as sister groups. Some Australian Nepticulidae have a pectinifer in the male genitalia which is also typical of the Opostegidae (absent from New Zealand), and in both families the moths have an expanded antennal scape ('eye caps') and comparable ultrastructures on the antennal segments. The Australian nepticulid species deserve early attention, since they seem to demonstrate a wider diversity of structure than the Nepticulidae of other regions so far studied.
It should be noted that not only Lepidoptera mine leaves; larvae of some weevils (Coleoptera: Curculionidae) and some flies (Diptera: Cecidomyidae, Agromyzidae, Drosophilidae) are miners. Diptera larvae that mine have distinctive mouthparts, with pharyngeal hooks or a sub-cephalic plate, and no recognisable head capsule; weevil larvae lack a spinneret ('sp' in Text-fig. la).
Nepticulid larvae are immediately distinguishable in New Zealand by their head capsule structure (Text-fig. 1 a), with a squat antenna, a more or less rectangular frons, and the left and right lobes widely separated and prolonged posteriorly: cf. Watt 1924, p. 677, fig. 4 - 8 (Nepticulidae) and p. 680, fig. 17 and 18 (Gracillariidae). Other leaf-mining lepidopterous larvae have the head capsule lobes touching, either at a point or along a line; if widely separated, the lobes are not prolonged posteriorly. Nepticulid larvae have a slender, sclerotised lateral bar on each side of the anal shield (Text-fig. 1b), and lack claws, visible forelegs, or crotchets. (The mining first and second instars of a New Zealand roeslerstammiid have lateral struts on the last abdominal segment, but these are irregular in shape, and the forelegs have claws.) A typical nepticulid larval head is shown in Text-fig. 1 a, and a dorsal view of an entire' larva in Text-fig. lb.
We were shown a damaged larva in a linear mine, recovered from a herbarium specimen of the rare shrub Teucridium (Verbenaceae) from Awahuri Reserve, Feilding WI, collected 23 December 1961 by A.E. Esler (NZAC). While superficially resembling a nepticulid larva it lacks both a spinneret and the characteristic lateral rods on the anal segment. Subsequently B.H. Patrick (pers. comm.) has searched without success for mines on Teucridium at Trotter's Gorge DN. We give details of this record to draw attention to the presence of an unknown miner on North Island Teucridium.
Nepticulid larvae are often heavily parasitised by Hymenoptera belonging - in Europe at least - to the families Braconidae (Ichneumonoidea) and Eulophidae (Chalcidoidea) . These are usually solitary parasitoids attacking and later emerging from the larvae (e.g., Chrysocaris), though sometimes they emerge from the pupa (e.g., Derostinus); few are gregarious. They are not usually host-specific, but may search for hosts on particular kinds of plants. Parasites recognised in New Zealand belong to the family Eulophidae.
The different genera of Nepticulidae were originally recognised on adult characters, particularly wing venation. Since they are so minute (wingspan 5 - 18 mm), these moths require special handling techniques, including preparation and examination of genitalia. This comparatively recent approach to study of nepticulids has reinforced the original generic divisions. Even more recently, stereoscan studies have revealed valuable diagnostic characters whereby, for example, even a single segment of the antenna may signify generic identity.
Extemally the moths worldwide tend to fall into four basic wing patterns which, under the microscope at least, are overlain by scales with a variety of iridescent colours of differing intensity. Thus, it is common to find very similar wing patterns in species which are not closely related - even in different genera. To add to the complexities of morphological study, genital structures may also be similar in different species. Therefore, species recognition may require a combination of morphological characteristics together with features of the life cycle, and sometimes even biochemical analysis is necessary.
Collecting leaf-mining Lepidoptera in New Zealand differs in three fundamental ways from the Northern Hemisphere.
- The preponderance of non-deciduous plants in the flora allows the presence of actively feeding larvae even above the winter snowline, and potentially permits increased size and voltinism.
- The majority of New Zealand species are on Asteraceae [Compositae], a host family of only minor importance in the Holarctic region.
- New Zealand is the only country known to have but one genus of Nepticulidae, viz Stigmella. Everywhere else that Stigmella is found the genus Ectoedemia also occurs, and usually other genera as well.
Stigmella is extremely widespread, as is Ectoedemia, and is associated with vascular plants on all continents. In the Holarctic region there is considerable similarity between the species of western Europe and those of North America.
The name Stigmella Schrank, 1802 is the senior subjective synonym of Nepticula Heyden, 1843. The valid name for the genus was long in dispute, but the position has been clarified by Wilkinson (1978), who gave detailed arguments based on the taxonomic history of the family and genus. The generic name has now been stabilised as Stigmella and the family name as Nepticulidae. The new combinations created by this situation have been formalised by Dugdale (1988).
Historical background
In Europe, leaf-mining microlepidoptera were known before the time of Linnaeus and his tenth edition of 'Systema Naturae'. For example, De Geer in 1752 thoroughly described the life cycle of the rose-feeding "Phalaene" leaf-miner and illustrated the major instars in some detail. Since then the number of described species has steadily increased; today some 470 are known in the western Palearctic region, with 245 synonyms. However, it is not unusual still to find new species in northern areas, and around the Mediterranean there are many new species awaiting a name and description.
In North America interest in leaf-miners began in the middle of the last century; there are now about 146 known species of Nepticulidae, but the real number is likely to be similar to that in Europe. In most countries studies did not begin until about 60 or 70 years ago, and this is the period when interest burgeoned in New Zealand.
The first New Zealand nepticulid was described by Francis Walker in 1864, but he did not recognise its affinities. He named the species Tinea maoriella from three specimens collected by Col. D. Bolton in Auckland AK. Its identity as a species of Stigmella has only recently been recognised.
Other early species were described by Edward Meyrick (1854-1938), who worked in New Zealand and Australia between 1879 and 1886 as a schoolmaster. During 1882 and 1883 he taught at Christchurch Cathedral Grammar School, but he left New Zealand in mid 1883 to take up a teaching position in Australia. He visited New Zealand on several occasions and collected new material, but he finally left for England in 1887 aged 33 years, and never travelled again. Three New Zealand species were described by Meyrick in England in 1889, but these were represented by unique holotypes collected as adults, and nothing was known about their host plants or life cycles. Meyrick described five further species between 1916 and 1924, again from one or two adult specimens collected by him or sent to him by G.V. Hudson (Hudson 1938). Meyrick's immense collection was presented to the British Muscum (Natural History) in 1939.
One further species now occurring in New Zealand was described in the last century - Stainton's microtheriella (1854). This is unique in being the only introduced species, and was brought into New Zealand from Britain around 1850. It was described from British populations, and is also unusual in being parthenogenetic and pupating on the stem of its food plant (Corylus avellana). Both characteristics played a major role in its introduction to New Zealand. The story is an interesting one (see p. 29).
That famous New Zealand entomologist George Vernon Hudson (1867 - 1946) took an interest in all insects, and with regard to Lepidoptera was guided by Meyrick's advice. In 1892 he published what for a long time was the only general book on New Zealand insects, 'Manual of New Zealand Entomology'. After 24 years' work he finished 'The Butterflies and Moths of New Zealand' in 1928; this, together with its 1939 supplement, is still the most comprehensive work on New Zealand Lepidoptera. There are many Nepticulidae in his collection, which is now deposited in the National Museum of New Zealand in Wellington. During Meyrick's lifetime Hudson gave him much of his material to be described, but in 1939 Hudson himself described "Nepticula sophorae".
Morris Netterville Watt (1892 - 1973) was a specialist on New Zealand's leaf-mining insects. He was a medical practitioner by profession, but as an amateur entomologist he amassed a substantial collection in his spare time. His detailed notes have been of great value to later authors. He described one nepticulid species in 1921 and another in 1924, and published eight papers on leaf-miners in 'Transactions of the New Zealand Institute' between 1914 and 1924. His collection too is now deposited in the National Museum in Wellington (Ordish 1974).
Another entomologist and naturalist who described New Zealand nepticulids was Alfred Philpott (1871 - 1931), a man of private means who lived in Invercargill SL during his early years. He compiled a checklist to the birds of Otago, and as an entomologist was primarily interested in Lepidoptera. From 1921 to 1929 he was curator of Lepidoptera at the Cawthron Institute in Nelson NN, and in 1930, after the Murchison earthquake of 1929, he moved to Auckland. He described "Nepticula lucida" in 1919 and "Nepticula insignis" in 1927. He is regarded as having contributed to modern interpretations of Lepidoptera structures.
The most recently described New Zealand nepticulid is Stigmella laqueorum (Dugdale, 1971). Many more specimens, often representing new species, have since been collected by John Dugdale (DSIR, Auckland) and Brian Patrick (Dunedin), who have also reared many species.
The present study
Nepticulidae have been the subject of intensive research at the Vrije Universiteit, Amsterdam, over the period 1978 - 1985. This family has held our attcntion not only because of the large number of hitherto unknown species, but also because of its intimate relationship - evolved over a very long time - with the host plants, and the interesting life cycles that are being elucidated. Groups within the family were studied using disciplines ranging from biochemistry to population biology, in order to discover something of the principles governing insect-plant relationships and evidence of co-evolution between the two. In connection with this work, systematic revisions of the nepticulid faunas of the western Palearctic, the Nearctic regions, South Africa, and Japan have already been completed (Wilkinson & Scoble 1979; Wilkinson & Newton 1981; Wilkinson 1981; Newton & Wilkinson 1982; Scoble 1983; Schoorl et al. 1985; Kemperman & Wilkinson 1986; Schoorl & Wilkinson 1986; also see Wilkinson 1987).
As a basis for our work on New Zealand's nepticulid fauna we have made collecting trips country-wide during July - September 1982 (CW), April - May 1984 (JHD), and May - June 1985 (CW). In addition we have borrowed material from the National Museum of New Zealand, Wellington; New Zealand Arthropod Collection, Entomology Division, DSIR, Auckland; and the British Museum (Natural History), London. Further specimens were borrowed from the private collcction of B.H. Patrick, of Dunedin. The rest of the material comes from our own collecting, and will largely be deposited in the above collections. Some duplicate specimens will go to the Instituut voor Taxonomische Zoology, Amsterdam.
In the New Zealand fauna 28 species are here recognised; 14 of them are new, the other 14 are redescribed. Twenty-six species are illustrated with genitalia figures for the first time. All primary types have been examined, whether in New Zealand or at the British Museum (Natural History).
It has not been possible to work out a meaningful phylogeny, nor is it practicable to divide the species into species-groups, as has been done with those of Europe. The New Zealand species are very closely related, and - the adventive microtheriella excepted - all seemingly evolved from common stock. Thus they may conveniently be retained in a single group. Certainly there are outliers (platina n.sp., progonopis, and hoheriae n.sp., for example), and a numerical analysis would prove interesting, but with such a small fauna splitting into groups is neither warranted nor justified. S. microtheriella is a member of the betulicola species-group of Johannson, a European species-group (Nieukerken 1986, p. 8).
Fossil evidence
CW examined more than 2000 leaf fossils at the New Zealand Geological Survey (DSIR, Lower Hutt) and in the Geology Department of Victoria University, Wellington. A few clear and unmistakable leaf mines were found from the middle Miocene; these are shortly to be described together with others, including two from North America found in deposits from the same period (CW, in preparation). Fossil leaves were found in the coal tips near Westport (NN - BR), but none had recognisable mines. It was also hoped to find mines in DSIR's material from Antarctica, but this was not to be.
CW has at present in his care the oldest known fossil leaf with distinct and irrefutable insect mines in it, which are exactly similar to those of Stigmella today. The fossil comes from Turonian Age (Upper Cretaceous) deposits in Kazakhstan, of about 110 million years ago. He has also collected wood from the Kellaways beds (140 mya) in England which contains tunnels resembling the borings of present-day beetle larvae, so undoubtedly the origins of such insect/plant relationships are much earlier than might be supposed.