Dichromodes Guenée, 1857

Young, Catherine J., 2006, Molecular relationships of the Australian Ennominae (Lepidoptera: Geometridae) and implications for the phylogeny of the Geometridae from molecular and morphological data, Zootaxa 1264 (1), pp. 1-147 : 1-147

Dichromodes Guenée

The 28S D2 data (Fig. 10), the morphological analysis (Fig. 16) and the combined molecular and morphological analysis (Fig. 17) all support the placement of Dichromodes euscia as basal to ( Ennominae + rest of the Oenochrominae + Geometrinae ). It is not grouped with the other representative of Oenochrominae s. l. in the analysis, Nearcha curtaria , or the robust­bodied oenochromines, adding weight to the contention that the Oenochrominae is not a monophyletic group ( Scoble & Edwards 1990).

Dichromodes is the largest genus (70+ spp.) ( McQuillan & Edwards 1996) of the slender­bodied Oenochrominae and is restricted to Australia and New Zealand. Some species feed on shrubby Myrtaceae but not Eucalyptus l’Hérit ( Nielsen & Common 1991) , implying an ancient host plant relationship at least as old as the late Cretaceous. Adults of this genus are typically coloured in shades of grey and brown. The forewings cover the hindwings at rest ( Common 1993). The adults of D. euscia are small moths with pale brown forewings with a conspicuous, dark brown, arched band on the postmedial line whereas hindwings are almost uniformly paler. The ansa in D. euscia tapers from base to apex, a structure considered primitive and typical of the Oenochrominae s. l. by Cook and Scoble (1996). However the ansa of D. stilbiata differs by being narrow at the base, widening to a broad flat surface and then narrowing apically, rather similar to geometrine ansal morphology ( Cook & Scoble 1992) while the ansa of D. confluaria shows an intermediate shape.

The larvae also exhibit a putatively primitive characteristic. New Zealand representatives of the genus have the full complement of SV setae, SV1­3, on abdominal segments 1–5. In other subfamilies, SV2 and/or SV3 are lost on one or more abdominal segments 1–5 ( Dugdale 1961). However there is some doubt that the New Zealand and Australian species are congeneric (J. Dugdale pers. comm.). New Zealand species feed on crustose lichens characteristic of stony habitats from coastal to alpine areas and including nival zones ( Dugdale 2001), whereas Australian species are restricted to vascular plants, where known, of the family Myrtaceae . Furthermore, the larva of an undescribed species of Dichromodes ( McFarland 1988) lacks the primary seta SV2 on A1 (Fig. 24), the common setal pattern found in the Ennominae , Larentiinae and Sterrhinae ( Singh 1953; Dugdale 1961).

Distinctive characters:

(1) SV1, SV3 and V1 setae on A1 not in vertical alignment (Fig. 24). This distinguishes this species from the Ennominae but not the Geometrinae , Oenochrominae s. str. and Sterrhinae .

Note: it is possible that this character is related to the shape of the caterpillar. Stout, robust caterpillars, such as the Australian Nacophorini have a more compressed setal configuration so that some setae are often aligned vertically. In long slender caterpillars such as those found in the Geometrinae , Oenochrominae s. str. and Sterrhinae , the setae are displaced horizontally resulting in the configuration as above.

(2) SD2 seta directly ventrad to D1 on the anal shield. SD2 is normally antero­ventrad of D1. However this character was found to be variable within the Australian asthenine genus Poecilasthena Warren (data not shown).

(3) Uniordinal crochets in the mature larvae. Biordinal crochets are more usually present in the mature larvae of the Geometridae ( Stehr et al. 1987) .

(4) Many distinct annulets on abdominal segments.

The pupa of Dichromodes sp. is relatively slender and has 4–5 pairs of cremastral setae ( McFarland 1988).

The divergence of Dichromodes from a relatively basal node in the geometrid phylogeny is supported by both molecular and morphological evidence. It would be very interesting to further pursue the study of this genus and in particular the identification of likely sister groups of this taxon.