Knowledge of the distribution of the Thyridoidea and Pyraloidea is complicated by four main issues:
i. The lack of a detailed re-evaluation of the taxonomy of the many morphotypes with very wide distributions. Do they constitute one species or many closely related species? In many species there has recently been a recognition of multiple synonymies and in some species these junior types have now been allocated sub-specific status.
ii. The disparate intensity of collecting from different parts of the region. The summary of collections in the Material Examined Menu subheading of the Introduction will indicate that the Malaysian parts of Borneo have been collected relatively intensively in recent years. By contrast the far larger area known as Kalimantan (Indonesian Borneo) has received practically no attention since the collection of Doherty in 1890 on Pulau Laut, off the southern tip of the main island (Kalimantan Selatan) or Samarinda (Kalimantan Timur) on the east coast. These specimens are now in the NHM. However Leiden has recent accessions from Pasir (Kalimantan Timur).
iii. The rarity of a species will also influence whether it will have been discovered widely and these species will present a discontinuous distribution. Some species are globally rare being restricted in geographic distribution but have large populations in the centre of their range. Such species are best described as local rather than rare. However others have small populations even in the centre of their distributional range (Novotny & Basset, 2000). Less easily explained is why in some biotopes there appears to be a large number of rare species giving alpha diversity distribution curves extremely skewed to the right. This may be a sampling effect. Where species richness is greatest, an individual species is more likely to be missed at a given level of sampling effort, leading to underestimates of range sizes in the species-rich tropics (Godfray et al. 1999). This problem of singleton specimens is referred to by Gaston (1991) who comments that ‘if the likelihood of catching a species at any one site is so low the proportion of species recorded between sites would be expected to be low even if they had identical faunas.
iv. Most of the specimens encountered are from collecting areas which have altered political status. This leads to some difficulty in interpreting data labels even where precise names are given. Previous regional names have changed, often several times, and the locality may be incorporated into newer political entities. Indeed they may be parts of two or more newer countries. This is especially true of the northern Indian subcontinent where the lowland areas at the head of the Bay of Bengal (often ‘Bengal’ on data labels) are now Bangladesh or India (Assam, Uttar Pradesh, Tripura, Mizoram). The Shillong Highlands (Khasis, Khassia, Khassia Hills), once part of colonial Assam, are now in the Indian state of Meghalaya. Most specimens whose labels give ‘Singapore’ should be treated with caution as, before about 1900, this name was often applied to specimens originating from a much wider area including the present day Malaysian state of Johor. In a few cases we have had to choose which currently accepted name to use. For example the correct name Myanmar is used. The former name, Burma is only used where this refers to original location data associated with a particular specimen.
A Gazetteer of locality names is provided (see Menu). In a few cases we have been unsuccessful in ascertaining the location given on the data label - although the search was intriguing!