Lithinini

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

Australian Lithinini — I. apicata and Metrocampa biplaga

Two bracken feeding Australian ennomines Metrocampa ada and M. biplaga were placed in this genus by Meyrick probably in error, as Metrocampa Bruand is a synonym of Campaea Lamarck ( Fletcher 1979) . These species were listed as lithinines by McQuillan and Edwards (1996). In the 28S D2 tree (Fig. 10) M. biplaga was placed deep within the Australian Nacophorini , well separated from I. apicata although these relationships were poorly supported. Sequence divergence between the two species was (6.5%). Adults of M. biplaga are large moths of variable colour and patterning but both wings are usually a uniform pale to greyish brown. The discal spot on the forewing is prominent and there is usually a row of small dark spots outlining the postmedial line. The moths are distinguished by a sharp angling of the outer margin of the forewing. Both lithinine genera share many adult morphological features including those listed above except for the following characteristics possessed by M. biplaga :

—swollen hind­tibia; U­shaped gnathos (Fig. 113); absence of discrete cornuti (Fig. 114); relatively small corpus bursae; absence of signa; inner surface of corpus bursae studded with small spicules (Fig. 115).

The eggs of the two species of Metrocampa are rather nacophorine in appearance with a broad, dorso­ventrally flattened form, irregularly arranged cells, narrow to moderately broad, recessed walls and inconspicuous aeropyles (Fig. 116) (Young, in press). They do not resemble the eggs of I. apicata (Fig. 112) or other lithinine species ( Salkeld 1983).

Shared larval features are as follows:

—fern feeders; moderately stout to stout; short setae; long setae on first instar; SV1, SV3 and V 1 in vertical alignment on A1; absence of extra prolegs; crochets a biordinal interrupted mesoseries although incompletely interrupted in I. apicata in mature larvae; acuminate setae.

The presence of moderately long to long setae in the first instar larvae is typical of the Australian Nacophorini (unpubl. data). Long setae were also found in Amelora , Capusa, Chlenia , Fisera , Mnesampela , Plesanemma and Thalaina Walker. However this feature was also present in the asthenine Poecilasthena and the noctuids Proteuxoa Hampson and Agrotis Ochsenheimer.

Differences between the larval morphology of M. biplaga and I. apicata :

—only four lateral setae present on A6; L3, SV1 and V1 aligned vertically on A3–5; anal claspers large and prominent; crochet arrangement in the first instar larva a uniordinal interrupted mesoseries, in M. biplaga only.

Behavioural differences between the two species is the tendency of I. apicata to drop, without the aid of silk, and rest in a coiled position when disturbed. On the other hand, M. biplaga larvae are stout and sluggish and conceal themselves while clinging to the undersides of fronds when disturbed. Adult resting positions also vary. The adults of Idiodes rest in typical geometrid fashion with all wings exposed in an open planiform position whereas Metrocampa adopts the more atypical closed planiform position in which the wings are held in a horizontal plane but with the hindwings covered ( McFarland 1988).

Shared pupal features are as follows:

—setae very short; exposed labium; concealed meta­tibia; pro­thoracic spiracle weak in I. apicata and absent in M. biplaga ; no A5 spiracular development; dorsal furrow welldeveloped in both species, deeply excavated in M. biplaga ; lateral furrow present in both species but weak in M. biplaga ; four pairs of hooked cremastral setae, terminal pair robust.

Unlike M. biplaga , I. apicata has a smooth rather than rugose cuticule and exposed fore­femora. The punctation in both species is also noticeably different. In I. apicata the punctation is uniformly small, shallow, dense and randomly distributed on A1–7 whereas M. biplaga has large, deep punctures arranged in two rows on the dorsum of A1–3, and then similar punctation to I. apicata on A4–8.

The Nacophorini and Lithinini have been linked on the basis of the probable homology of the processes of the anellus found in both tribes and also the curved edges of the juxta that often bear cristate hairs ( Rindge 1986; Pitkin 2002). Rindge (1986) in his review of New World Lithinini found difficulty in defining apomorphies for the tribe. However Holloway (1987) defined the tribe on the following features: projected cucullus; presence of processes of the anellus, apices of processes often bearing spines; valvae directed dorsally; triangular transtilla; uncus long and slender; weak, setose socii; central signum; pleated, short ductus bursae. I. apicata presents all of these features (Figs 109, 111); however none, apart from possibly the modified cucullus, are unique to the Lithinini . The genitalia of M. biplaga are not typically lithinine due to the absence of a projected cucullus and signum (Figs 113, 115).

It is probable that M. biplaga has been misplaced into the Lithinini despite being a fern­feeder. Non­lithinine fern­feeders in the Geometridae are few, as far as I know, but one example is the genus Scionomia Warren ( Sato 1977) , which is placed in the Ennomini . The genitalia and eggs of M. biplaga and its congener ada lack typically lithinine features and the larvae of biplaga are differentiated from I. apicata on several important features. Further, the presence of a combination of all three male secondary sexual characteristics, A3 pecten, inflated hind­tibia and hair­pencil on the hind­tibia in this species were only found in the Australian Nacophorini in this study (unpubl. data) and is additional evidence of a link between biplaga and the Australian nacophorines. Accordingly, both lithinine genera have been placed within the Australian Nacophorini by the molecular analysis (28S D2) (Fig. 10) and it is possible that the two tribes could be united, as the monophyly of the Lithinini is only weakly supported on morphology.