The Uraniidae have recently been the subject of detailed morphological investigation by Lees & Smith (1991) and Minet (1994[5]), extending previous work by Sick (1937) and Minet (1983, 1986, 1991): see also reviews by Common (1990) and Scoble (1992).

The most striking, definitive feature of the family is the occurrence of sexual dimorphism in the position of the tympanal organs, as well as their general structure. Whilst those of females are in a similar position to those of the Geometridae, ventrally at the base of the abdomen, those of the male occur laterally between the second and third tergites (Figs 159-168). Minet (1994[5]) indicated that, whilst the cuticular components of these organs in males and females are not homologous, the sensory components (scoloparia with only two scolopidia instead of four) may well be. The subfamily Auzeinae has a somewhat different structure in the male tympanal organ to that of the other uraniid subfamilies, leading Minet (1994[5]) to suggest it was the most primitive lineage of the group (See Auzeinae).

The forewing venation provides another family characteristic, lacking the areole seen in numerous lineages of the Drepanoidea and Geometridae, and having R3+R4 as the terminal bifurcation of the Rs system, with R5 well separate from this system, sharing a common stalk, or, more rarely, being connate with M1 (Holloway, 1986a: fig 23). R2 may arise independently from the cell or branch off basally from R3+R4. However, some Epicopeiidae have a similar venation system in the forewing (See Epicopeiidae). There is also a diagnostic sclerite in the metathorax (Minet, 1983; Lees & Smith, 1991), though this is absent from the Auzeinae (Minet, 1994 [5]).

The moths are generally of delicate build with deep triangular forewings and, with the exception of the Auzeinae, tailed or angled hindwings. The veins associated with these tails vary from subfamily to subfamily, tending to be Rs and M3 in the Epipleminae, M3 in the Microniinae, M1 and M3+CuA1 in two-tailed Uraniinae and M3 in single-tailed genera. Forewing pattern is usually repeated on the hindwing except in some Epipleminae, though in all groups the hindwing is patterned. Chaetosemata are large and ocelli are absent.

The male genitalia usually lack a gnathus. The female has a rounded corpus bursae with a single signum, weakly or strongly spined, in a central to subbasal position.

The eggs are domed, spherical with projecting ribs, deposited in an upright position. The larvae usually lack secondary setae and have the primary setae on raised pinacula. The pupal cremaster has four pairs of hooked shaftlets, though these may be reduced in some genera (e.g. to two in Acropteris Geyer).

The relationship of the subfamilies in Fig 1 was suggested by Smith & Lees (1991) and Minet (1994[5]). The non-auzeine subfamilies share the metathoracic sclerite referred to above, and strong modification of the anterolateral areas of the male third abdominal tergite.

Figure 1. Phylogeny of the Macrolepidoptera as suggested
and Minet (1991) and Kristensen & Skalski (in press). Superfamilies are indicated in capitals. Groups treated in this work are indicated in bold.

The sister-relationship between the Uraniinae and Microniinae is indicated by Minet (1994[5]): loss of the frenulum and retinaculum with development of amplexiform wing coupling (a weak humeral vein may be present); the condition of the mesothoracic presternum, with fairly short ventral arms, the membrane between them vestigial; a short scoloparium in the male, attached to the convex anterior area of the tympanum, the posterior part being covered with many fine, parallel strigae. In addition, the hindwing has only one anal vein (though this condition also occurs in the Auzeinae and some Epipleminae), and the wing pattern usually involves strong transverse striae.

Males in some species of both the genera discussed below (the type species of Decetia Walker, its close relatives and D. subflavata Warren; the new species of Brachydecetia nom. n.) have CuA2 in the hindwing arising from the cell in an unusually basal position.

There is some host-plant specialisation within the subfamilies (Lees & Smith, 1991), with Uraniinae only reliably recorded from Euphorbiaceae and Microniinae from Asclepiadaceae. The Epipleminae exploit a wider range of families, but there is specialisation at a generic level as discussed later. The only records for the Auzeinae are from the Olacaceae and the related family Opiliaceae.

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