Lepidoptera

Kristensen, Niels P., Scoble, Malcolm J. & Karsholt, Ole, 2007, Lepidoptera phylogeny and systematics: the state of inventorying moth and butterfly diversity, Zootaxa 1668, pp. 699-747 : 708-711

Inventorying the Lepidoptera : status and biases

Gaston (1991a: 286) was undoubtedly correct when writing that "The Lepidoptera are generally regarded as the best collected and studied of the four major insect orders". However, on a global scale this general belief is in itself probably incorrect. The advanced levels of butterfly and hawk/emperor moth taxonomy and of inventories of some very restricted Northern Hemisphere Lepidoptera faunas have little bearing on the overall status of systematic lepidopterology. The major tasks for delivering this more comprehensive picture lies in dealing with the world fauna of moths. The sampling of tropical moths has so far been very inadequate, and where samples have been made they have often not been worked up. This situation is significantly explained by the work of Gaston & May (1992). These authors found, on the basis of surveys of insect systematists in North America and the UK, that of the four major insect orders the Lepidoptera actually have the smallest taxonomic workforce. The same situation then pertained also in Australia (pers comm. from the late E.S. Nielsen). This situation is unlikely to have changed today.

From their survey, Gaston & May (1992) indicated that about 80% of present-day insect taxonomists then were based in North America and Europe, a figure unlikely to have changed much subsequently—except, probably, for some E. Asian countries. Taxonomy also has had longstanding strongholds in other industrialized countries such as Japan, Australia and New Zealand. It is therefore to be expected that the faunas will be better known in these regions than elsewhere, but it must also be noted that to several workers based here certain tropical areas ( Taiwan, Borneo, Costa Rica, etc.) have recently been of focal interest.

Experience shows, that large-scale elucidation of life-histories of the insect fauna of a given area is feasible only for those workers who are at least largely resident in that area. The knowledge of Lepidoptera immatures is, therefore, even more geographically biased than that of the adult insects.

‘Patriotism’ has also made its mark on our knowledge of distribution in Lepidoptera , particularly in terms of the activities of non-professionals. 'Patriotism' in this context means the sum of linguistic and traditional/ cultural barriers, which restrict the activity of a worker to the study of her/his national fauna. Perhaps the most striking evidence of this mechanism is the markedly more detailed knowledge of the moth fauna, particularly of the micro-moths, of Europe compared with that of any N. American area. So many N. American lepidopterists remain 'butterfly workers', since they feel few barriers to extending their interest to the butterfly fauna of the entire Nearctic region. In contrast, the average amateur lepidopterist, at least in some European countries, having exhausted the challenges (at the collectors' level!) presented by the local butterflies, has been more likely to proceed to the study of the macro-moths, and often also the micro-moths, of the national fauna, rather than to butterflies of neighbouring countries. This explains why in some countries even the most minute micro-moths are now known in much greater detail than larger and more striking wasps, flies etc. Having said that, an increasing number of European amateur specialists in recent decades have extended their interests, and descriptive efforts, to Lepidoptera faunas outside their native regions.

A provisional survey of the described world fauna of Lepidoptera , by family-group taxa and zoogeographical regions, was published by Heppner (1991) (minor updates are given by Heppner 1998). This survey was based partly on actual counts from the literature, partly on the card indexes in the Natural History Museum (London) and the National Museum of National History (Washington), and partly on estimates (the source is uncertain in many cases). Clearly this task was a difficult one, and Heppner rightly underscored the uncertainties of the figures. Herbulot (1992) and Scoble et al. (1995) highlighted these uncertainties by comparisons with (near-)exact counts of Geometridae , which for some regions and/or subfamilies differed markedly; for instance the figure for Afrotropical species proved to be almost 50% higher than Heppner's. It so happens, however, that the inexactitudes in Heppner’s figures largely cancel out mutually, hence his grand total for world Geometridae (20,890) is remarkably close to the figure by Scoble et al. (21,144), and similarly his estimated total for world Lepidoptera (146,565) is remarkably close to the estimates given about the same time by Holloway et al. (1987) and Hammond (1992). The number of described species is now probably some 160,000.

Table 1 shows a geographical breakdown of Heppner's global numbers of described species. Heppner noted that the Neotropical Lepidoptera fauna is considerably more species-rich than that of the Oriental, and he attempted to find explanations for this observation. He noted, for instance, that the Neotropical region covers by far the larger land area of the two. From Table 1 it is clear that when one combines Heppner's 'Oriental' and 'Australian' regions into an 'Indoaustralian' region (a concept which will be familiar to users of the monumental 'Macrolepidoptera' manuals edited by A. Seitz), the latter has a land area that is very similar to that of the Neotropical region. The two regions are also roughly comparable with respect to north-south extent, and their Lepidoptera diversities, crudely expressed as species per unit area, are then seen to be very similar indeed. The main issue, which arises from the geographical survey is, therefore, the markedly lower species-per-unit-area figure for the Afrotropical region. This pattern, which is found repeatedly in global biodiversity surveys, more than 30 years ago prompted Richards (1973) to refer to Africa as the “odd man out”, and it continues to attract biogeographers' attention.

To examine patterns of species description in Lepidoptera it is worth considering separately those three major assemblages of the order with which lepidopterists are familiar. Historically, work on these groupings have followed rather different paths. These groupings are 1) The micro-moths, which embrace the more primitive lineages within the order, 'up to', and including, the 'pyraloid grade' superfamilies (mostly small (sometimes minute) moths with larvae usually feeding internally or concealed on their host plants. 2) The macromoths, i.e., the predominantly night-flying members of the Macrolepidoptera, which may, or may not, be monophyletic. The Macrolepidoptera are medium-sized to large insects, the larvae of which are often external feeders. 3) The butterflies, a presumably monophyletic entity that may be cladistically subordinate within the Macrolepidoptera; nearly all adult butterflies are diurnal, and many have particularly colourful wing patterns.

Fig. 5 illustrates some trends in the taxonomic research on the three groupings during the latter half of the post-Linnean era, showing the numbers of new species descriptions (A) and new species synonyms (B) published during six three-years periods since the establishment of Zoological Record in 1864. One general trend, which is observable in all curves of new species descriptions, is a marked decline towards the fourth period (mid-twentieth century), followed by a more or less pronounced subsequent rise. However, the concordant curve shapes have different backgrounds, as has already been pointed out by Strong et. al. (1984) in their comments on similar statistics for a variety of phytophagous insect groups. In the case of the butterflies there can be no doubt, that the overall decrease in new species descriptions since a century ago reflects a genuine, even pronounced, drop in the number of species which still remain to be discovered/named. In the cases of the moths the drop reflects the change in the working practice of leading taxonomists, who no longer looked favourably on species descriptions "divorced from revisional or monographic work" (as expressed in Mayr, Linsley & Usinger's influential 1953 manual). Also, examination and specimen preparation procedures had become much more time-consuming, with descriptions/illustrations of genital structures eventually being considered mandatory ingredients in a worthwhile taxonomic study.

FIG.URE 5. New species described (upper) and new synonyms (lower) established for micro-moths, macro-moths and butterflies during six 3-year periods from the start of Zoological Record.

The preparation of permanent slide mounts of the genitalia has been a much more widespread practice among Lepidoptera taxonomists than among those working on insects of several other orders (who often are content to observe the organs at dissection microscope magnification only, with preparations stored in glycerol or even mounted dry on cards). This is undoubtedly primarily rooted in tradition, and it may in no small measure be due to the early influence exerted by F. N. Pierce on the British lepidopterists' community, including, eventually, the staff of the Natural History Museum, London. Unquestionably, this practice has enhanced appreciation of small, taxonomically significant structural details. Moreover, carefully prepared permanent mounts often are excellent objects for photomicrography and they provide maximum protection for minute dissected parts, which is an important consideration in the case of primary types particularly. On the other hand, it is sometimes crucially important to retain the possibility of examining the structures from different angles and/or to avoid any kind of distortion from a cover glass. Also, the time expenditure involved in consistent preparation of high-quality slide preparations (see Robinson 1976) can be difficult to justify in those cases where examination of many specimens is desirable or necessary. Here the storage of genitalia preparations in glycerol and associated with the pinned specimens, is often a satisfactory solution. (The availability in recent decades of light-weight plastic vials with silicone rubber stoppers has largely eliminated those misgivings about the vial-storage method, which were justified, when only glass vials with cork stoppers were available.)

If certain technical advances become routine requirements in taxonomy, further impositions are likely to be placed on taxonomists. Detailed microscopical observation of many skeletal features (see, e.g., Lee & Brown 2006), SEM examination of scales and antennal sensilla and, increasingly, molecular barcoding are notable examples. Even if taxonomists themselves are not involved in laboratory procedures, the removal, storage and recording of tissue samples are likely to prove to be time consuming. In contrast, other innovations (such as electronic description templates, high-quality imaging, of entire specimens and morphological details including slide mounts) may make conventional procedures less labour-intensive. The net consequences for throughput in revisionary Lepidoptera taxonomy remain to be seen.

Fig. 5 (lower graph) reveals a disconcerting observation for the abovementioned tightening of working practices, namely the legacy of synonyms created during phases of unconcerned mass-descriptions.

Species concepts. Any discussion of species diversity must in principle make reference to the species concept adopted. If asked, most taxonomists would probably say that their species are inferred to be reproductively isolated, and that morphological distinction is a surrogate measure of reproductive disjunction. In practice, most species are described on the basis of the kind of morphological differences (sometimes informed by natural history observations) traditionally used – many species being described before the biological species concept was articulated. This gives some reassuring constancy to those interested in using taxonomic data for understanding species diversity. Should, however, alternative species concepts be introduced, such as inflating subspecies to the level of species, our assessment of species numbers might change significantly.

Tables

TABLE 1. Regional distribution of Lepidoptera species diversity. PAL: Palaearctic; NEA: Nearctic; NET: Neotropical; AFT: Afrotropical; INA: ' Indoaustralian'. Source: Heppner (1991).

	PAL	NEA	NET	AFT	INA
Species	22,465	11,532	44,791	20,491	47,286
Area (mio sq mi)	18,751	8,817	7,202	9,796	7,449
Sp / area	1.2	1.3	6.3	2.1	6.3