The epigamic behaviour of euplœa (crastia) core asela (Moore) (lepidoptera danainæ) - with a description of the structure of the scent organs - A—The telegamic (courtship) flight of the male E. core asela

Abstract

Fritz Müller appears to have been the first to make systematic observation and to give accurate descriptions of the scent-producing and scent distributing organs of lepidoptera. Translations of his papers published on this subject form the Appendix to Longstaff’s “Butterfly Hunting in Many Lands” (1912). In course of the first of these, loc. cit ., p. 612 (Müller, 1877), he writes “having therefore demonstrated . . . that the purpose of the brushes and hair-tufts in the males [of certain species] is to exhale scents, which are probably agreeable to their females and entice them to pair, I am led to infer that this is the meaning of all similar structures on the wings of male lepidoptera, not only because of the unmistakable similarity amidst such great diversity [of systematic groups], but even more on account of the . . . peculiarities which render them especially suitable for such a purpose. They are usually sheltered from the air . . . while at rest. Thus the scent is not diffused at the wrong time and so wasted . . . One could hardly find a more effective method of employing any odoriferous substance than that of saturating with it the hairs of a brush, and then suddenly opening them out in all directions, so as to provide an enormous surface for evaporation.” Longstaff (1912) brought together the numerous observations made by himself and Dixey on the scents of butterflies in many parts of the world. Some of these are scents pleasant to our own olfactory sense, e. g ., the lemon-verbena of the male Green-veined White. Dixey (1909 to 1932) has investigated the external structures which are concerned with the production and distribution of the scents, devoting special attention to the specialized scales on the wings of male Pierines; while the minute anatomy of internal organs, such as anal glands and their accessory structures, of many species have been described and figured by Eltringham (1913 to 1929 and 1934) and Freiling (1909). Structures that are almost certainly analogous occur among Neuroptera and Trichoptera; and these too have been described by Eltringham (1919, 1931, 1932) and Mosely (1919). Field observations on the use and employment of these contrivances among lepidoptera have been recorded by Carpenter (1914-1927), Champion (1930), Fyson (1930), Lamborn especially (1911 to 1921), and Lever (1931). Lamborn, on more than one occasion witnessed the application of the distributing apparatus, the anal brushes, of certain Danaines to the scent-producing brands of the wings; and at the same time “experienced a sensation as if an aromatic snuff had impinged upon the mucous membrane of my nostrils.” Lever, too, describes the smell of the scent glands of certain Fijian species of Euplœa ; as “like that of burnt ginger-bread or caramelized toffee.” The names of some of those who have interested themselves in this subject are given in the references. It has been assumed that when both sexes are alike equipped with scent-organs the aroma given forth serves as a deterrent against insect-eating enemies; and, on the other hand, that when possessed by one sex only it serves to attract mates. Proof of this latter assumption has long been familiar in the “assembling” of male moths attracted, often from a great distance, by a virgin female of the same species; but, except in the moths Hepiatus hectus and H. humuli , proof of the converse phenomenon, female attracted by male, has not hitherto been forthcoming; though Carpenter’s observations (1914, 1927) show that the males of Amauris psyttalea and Danaus chrysippus make persistent attempts at close quarters to attract the females.