A survey of androconial organs in the Riodinidae (Lepidoptera)

The existence of specialized scales in adult male Lepidoptera has long been recognized, and they were first named androconia by Scudder (1877). Müller (1877a) believed that such structures had evolved as a result of sexual selection and that they were involved in the dissemination of scents or pheromones to influence female behaviour, a theory that has now been proven by experiments on the courtship of nymphalid and pierid butterflies (Tinbergen, 1941; Magnus, 1958; Brower et al., 1965; Pliske & Eisner, 1969; Rutowski, 1977). While such ethological and chemical studies remain scarce, more accounts exist of the gross occurrence and structure of butterfly androconial organs, but these typically address only one or two species. Broader studies, including general overviews (Müller, 1877a; Barth, 1960; Vane-Wright, 1972a; Boppré, 1984), and surveys of higher groupings, such as the Papilionidae (Miller, 1987), Pieridae (Dixey, 1913, 1932), Nymphalidae (Danainae: Müller, 1877b; Boppré & Fecher, 1977; Ackery & Vane-Wright, 1984; Boppré & Vane-Wright, 1989) and Lycaenidae (Eliot, 1973) are rarer. No such broad studies exist for the family Riodinidae. This paper presents an overview of the occurrence and ultrastructure of androconial organs in the Riodinidae, with discussions on their function, where known, and systematic significance. Modified scales found in both sexes, such as the abdominal setal tufts in Stalachtis Hübner, 1818 (Harvey, 1987), are assumed to be used for defensive purposes (Müller, 1877a), and are not considered here. The Riodinidae contains approximately 1300 species, the large majority of which are confined to the Neotropics (all subfamilies except the Nemeobiinae), where the family constitutes 15–20% of the total butterfly fauna (Heppner, 1991; Robbins et al., 1996). Although the group is conspicuous for its external and internal morphological and ecological diversity, its systematics and biology are perhaps the most poorly known of any butterfly group. What little is known of mate location and courtship behaviour in riodinid butterflies, and the fact that many genera exhibit seemingly tight niche packing (Hall 1999a), suggests that androconia should be widespread and varied in the family. The males of many species consistently perch in the same small welldefined areas, typically along streams, at forest edges and on hilltops and ridgetops, in much the same manner that birds and other vertebrates and insects have been described to lek (Höglund & Alatalo, 1995) (Fig. 1). Such prominent topographical features are believed to act as rendezvous sites for the sexes that enhance mating success in rare species (Scott, 1968, 1975; Shields, 1968; 1983). It is well established that A survey of androconial organs in the Riodinidae (Lepidoptera)