British Insects: the Families of Lepidoptera
British Insects: the Families of Lepidoptera | |
Comments. Melanin is a complex of dark (black, brown, yellowish or dull red) animal pigments, and “melanism” in the present context is the occurrence in a species of some individuals that are darker than the typical form, due to a heritable increase in the proportions of melanins in the epidemis (cf. Kettlewell, 1973). Melanism occurs in numerous moth species. In some it is known only as a very rare, recessive mutation, but others exhibit populations in which melanic individuals are common or even predominant in certain habitats and/or geographical locations. Inheritance of persistent melanism in moths is sometimes unifactorial, involving two alleles of a single gene with melanism dominant, or resulting in heterozygotes that are more or less intermediate. In other cases, more than two alleles may be involved at the same locus; and in still others, the phenomenon is multifactorial, with alleles at different loci operating cumulatively and resulting in complicated patterns of inheritance leading to populations comprising extremes and intermediates. In fact, melanism in the most intensively studied species, the Peppered Moth, principally seems to involve five alleles at one locus. Of these, the three responsible for the insularia (intermediate) complex of forms are dominant over the typica (normal) allele, while the carbonaria (fully melanic) allele is dominant over all of them; and the situation may be further complicated by the operation of modifier genes at other loci. In view of the complicated genetic background in the few cases that have been thoroughly investigated, and bearing in mind that few moth species have been genetically analyzed in this context, it will usually be impossible to assign field collections to genotype with any confidence.
From an evolutionary standpoint, persistence of melanic populations in relatively natural habitats (“rural” or “non-industrial” melanism) is sometimes reasonably interpretable with reference to Darwinian natural selection, as in the genus Spilosoma, although few cases have yet been thoroughly investigated (see Majerus, 1998 and 2002). However, spectacular changes in the proportions of melanic versus “normal” individuals in the populations of some moth species have been observed, quantitatively detailed and scientifically investigated in Britain for over a hundred years. Being rather obviously correlated with probable habitat pollution consequent on industrialisation, this phenomenon has long been termed “industrial melanism”. In the case of the Peppered Moth (Biston betularia) in particular, a causal relationship involving Darwinian selection has been rather convincingly demonstrated via numerous, laborious experiments. Researchers’ disagreements over experimental design and interpretation of results against the complex background of population genetics and ecology have led to spurious claims by religious extremists, who are unable to grasp that the obvious fact of organic evolution is unaffected by arguments over the precise mechanisms. In fact, neither the reality of biological evolution, which has been apparent to intelligent observers for more than two centuries (cf. Lamarck, 1801), nor the truism of Darwinian natural selection (that the fittest to survive will survive), have ever needed support from the Peppered Moth and "industrial melanism"; and in any case, they are more readily exemplified nowadays by micro-organisms and viruses, most spectacularly with reference to antibiotic resistance and new strains of influenza.
Our photographs of melanic moths depict specimens in Watson’s collection, and in effect constitute a snap-shot - by no means comprehensive - of the phenomenon as manifested around the North Staffordshire market town of Leek, in the decade 1948–1958. The mercury vapour light-trap was not then available, and moths were collected by day mainly by searching tree trunks and disturbing foliage, and by night using a pressure lantern in the field, at street lamps or at lighted windows; supplemented by searching for larvae and by ‘pupa digging’. The habitats, though all ostensibly “rural”, are located about 10 miles and 30 miles respectively from the heavily industrialised regions of Stoke-on-Trent and Manchester. If implementation from the early 1960s of the “Clean Air Act” has had a noticeable effect on industrial melanism in the moth fauna around Leek (see Majerus, 2002), it should be readily observable in the re-appearance of “normal” (i.e., light) forms of such common species as the Peppered Moth, the Pale Brindled Beauty and the Mottled Beauty!
The following list indicates examples of melanism illustrated either under the appropriate family descriptions in the present package (‘The families of Lepidoptera’), or in the generic descriptions in our accompanying ‘Geometridae’ or ‘Noctuidae’ packages, with references to the phylogenetic status of melanism largely following Ford and Majerus. “Non-industrial to industrial” here implies occurrence of melanics in natural, unpolluted habitats, with observed increased proportions of them in habitats affected by industrialization.
Arctiidae: Diaphora mendica (Muslin Moth: non-industrial, with sex-linked melanism predominant in the male); Spilosoma lubricepida (White Ermine: non-industrial); Spilosoma lutea (Buff Ermine: non-industrial). Geometridae: Agriopis leucophaearia (Spring Usher: non-industrial?); Agriopis marginaria (Dotted Border: non-industrial?); Alcis repandata (Mottled Beauty: non-industrial to industrial); Angerona prunaria (Orange Moth: non-industrial); Biston betularia (Peppered Moth: industrial) Ectropis crepuscularia (Engrailed: non-industrial to industrial); Epirrita dilutata (November Moth: industrial); Erannis defoliaria (Mottled Umber: non-industrial); Odontopera bidentata (Scalloped Hazel: industrial); Peribatodes rhomboidaria (Willow Beauty: non-industrial to industrial); Phigalia pilosaria (Pale Brindled Beauty: non-industrial to industrial). Lymantriidae: Lymantria dispar (Gypsy Moth: sex-linked melanism predominant in males); Lymantria monacha (Black Arches: non-industrial). Noctuidae: Allophyes oxyacanthae (Green-Brindled Crescent: non-industrial to industrial; Apamea monoglypha (Dark Arches: non-industrial to industrial); Apamea crenata (Clouded-bordered Brindle: non-industrial to industrial); Mesapamea secalis (Common Rustic: non-industrial to indistrial); Noctua fimbriata (Broad-bordered Yellow Underwing: non-industrial?); Noctua pronuba (Large Yellow Underwing: non-industrial to industrial?); Oligia strigilis (Marbled Minor: non-industrial to industrial?); Polia nebulosa (Grey Arches: industrial). Oecophoridae: Diurnea fagella (March Dagger: non-industrial to industrial). Thyatiridae: Ochropacha duplaris (Common Lutestring: non-industrial to industrial).
Illustrations. • Melanic Arctiidae: Spilosoma lubricepida (ab. walkeri Curtis. White Ermine, melanic variety). B. Ent. 92). • Melanic Arctiidae: Spilosoma lutea, S. lubricepida and Diaphora mendica (Buff and White Ermines, Muslin): photos. • Melanic Geometridae (1): Biston betularia (Peppered Moth, pale and melanic forms), cf. Biston strataria (photos). • Melanic Geometridae (2): Apocheima pilosaria (=Phigalia pedaria): light and dark forms, photos. • Melanic Geometridae (3): Alcis repandata and Peribatodes rhomboidaria (Willow Beauty: photos). • Melanic Geometridae (4): Ectropis crepuscularia (Small Engrailed) and Odontopera bidentata (Scalloped Hazel): photos. • Melanic Geometridae (5): Agriopis leucophaearia (Spring Usher), A. marginaria (Dotted Border), A. aurantiaria (Scarce Umber): polymorphism and melanism (photos). • Melanic Geometridae (6): Epirrita dilutata (November Moth): pale and melanic forms (photos). • Melanic Geometridae (7): Angerona prunaria (Orange Moth: colour variants, photos). • Melanic and polymorphic Geometridae: Erannis defoliaria (Mottled Umber: variation in males, photos). • Melanic Lymantriidae: Lymantria dispar (Gypsy) and L. monacha (Black Arches), photos. • Melanic Noctuidae (1): Allophyes oxyacanthae (Green-Brindled Crescent, photos). • Melanic Noctuidae (2): Apamea monoglypha and A. crenata (Dark Arches and Clouded-bordered Brindle, photos). • Melanic Noctuidae (3): Mesapamea secalis (Common Rustic, photos). • Melanic Noctuidae (4): Polia nebulosa (Grey Arches, photos). • Melanic Noctuidae (5): Noctua pronuba and N. fimbriata, with N. janthe, N. comes and N. iterjecta (Yellow Underwings, photos). • Melanic Noctuidae (6): Agrotis exclamationis (Heart and Dart: photos). • Melanic Noctuidae (7): Oligia strigilis (Marbled Minor, photos). • Melanic Noctuidae (8): Orthosia incerta (Clouded Drab, photos). • Melanic Oecophoridae: Diurnea fagella (March Dagger, photos). • Melanic Thyatiridae: Ochropacha duplaris (Common Lutestring: photos).
To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.
Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2003 onwards. British insects: the families of Lepidoptera. Version: 18th September 2008. http://delta-intkey.com’.
