Spilomelinae (Allyson, 1984)

Singh, Navneet, Ranjan, Rahul, Talukdar, Avishek, Joshi, Rahul, Kirti, Jagbir Singh, Chandra, Kailash & Mally, Richard, 2022, A catalogue of Indian Pyraloidea (Lepidoptera), Zootaxa 5197 (1), pp. 1-423 : 42

2.11. Spilomelinae

Diversity and distribution: the largest subfamily within the snout moths ( Pyraloidea ), and with 4,126 species in 341 genera, represents almost one third of the total Pyraloidea diversity (Nuss et al. 2003–2022, Léger et al. 2020). From India, 631 species in 161 genera are reported, representing 15.29% of the global Spilomelinae diversity. Of the 161 genera reported from India, 66 genera are known by only a single species each, and 84 genera comprise equal to or fewer than 10 species. Seven genera contain 11 to 20 species, and only four genera, Palpita Hübner , Syllepte Hübner , Patania Moore and Glyphodes Guenée , are represented by over 20 species ( Fig. 30 ). In India, the subfamily is most diverse in North East with over 350 recorded species, followed by the central Himalaya and the Western Ghats. In contrast, the Trans-Himalayan and Desert biogeographic zones are represented by very few Spilomelinae ( Fig. 31 ).

Adult characters: diverse in shape and size, with wingspans ranging from under 15 mm e.g., in Metasia Guenée , up to 90 mm in the species of Siga Hübner and Eporidia Walker. Due to the morphological diversity of the subfamily, only few characters are common to all Spilomelinae . Mally et al. (2019) found three synapomorphies for Spilomelinae that distinguish them from the sister-group Pyraustinae : the maxillary palps are minute to obsolete, the fornix tympani projects in ventral direction from the tympanal plane, and the ductus bursae of the female genitalia is weakly sclerotised or with a granulose texture. Chaetosemata are absent, ocelli mostly present. The labial palps vary from porrect to upturned. The proboscis is well-developed with a few cases of reduction, and absence in the myrmecophilous Niphopyralis Hampson. The antennae are usually simple, but with specialised basal segments in the males of some groups (e.g. Agroterini , Asciodini and Hymeniini tribes). Wing coupling is through two frenulum bristles in the females, and one in the males, a retinaculum hook is lacking. The praecinctorium of the tympanal organs is mostly bilobed. In male genitalia, the uncus is diverse in extension and shape, from reduced to well-developed with one or two bulbous, setose heads, in the tribe Margaroniini often with a complex three-dimensional uncus head structure and patches of differently structured setae. The shape of the valvae ranges from narrow and elongate to broad and paddle-shaped, the costa in the “euspilomeline” tribes is usually convex, whereas it is mostly straight or concave in the “non-euspilomeline” tribes ( Mally et al. 2019). Inner surface of valvae often bear claspers. Many species exhibit coremata articulating with the vinculum, and in Margaroniini they become most complex, bearing various patches of sometimes intricately shaped piliform scales on several coremata sclerites. The sclerotisation of the phallus apodeme is usually reduced to a narrow strip in the euspilomeline tribes, cornuti are often present, in Margaroniini typically one long needle-shaped cornutus. The shape of the female genitalia is varied, with the ductus bursae ranging from short to long and from slim to broad. The corpus bursae is with or without signa, in some taxa, a membranous appendix bursae is present—a structure that is otherwise typical for Pyraustinae and other subfamilies ( Mally et al. 2019).

Larval characters: morphologically, Spilomelinae caterpillars cannot be distinguished from those of the sister-group, Pyraustinae . Last instar larvae exhibit setae L1 and L2 on the prothorax and A1–A8, one SV seta on the meso- and metathorax, and one L seta on A9. Furthermore, the distance V1–V1 between the ventral setae is smaller on A9 than on A10. Some Spilomelinae in some genera, for example Conchylodes Guenée , Herpetogramma Lederer , Nomophila Hübner and Omiodes Guenée , have the dorsal (D) and subdorsal (SD) pinacula fused on the mesothorax and/or the SD pinaculum reduced on A2 and A7 ( Allyson 1984).

Food plants: like the morphology, hostplant use is diverse in Spilomelinae . The larvae are webbers, tiers, folders or rollers of leaves, or stem-borers. Several tribes seem to be more or less confined to one or a few hostplant families: Hydririni mostly feed on Sapindaceae and Convolvulaceae , Lineodini on Solanaceae , the Cnaphalocrocis Lederer group of the tribe Spilomelini includes a major radiation especially on grasses ( Poaceae ), where they can become pests of rice, corn and other agricultural grains. Asciodini larvae are commonly associated with herbaceous plants of the order Caryophyllales . Trichaeini generally feed on Rubiaceae , and some are considered pests of coffee. Rubiaceae might also be the primary hostplant family for Nomophilini , from which the group has radiated onto other hostplant families. The larvae of Steniini, as far as known, are detritivores. Hymeniini , Udeini and Agroterini larvae have a diverse spectrum of food plants, in the latter, significant hostplant associations are with Rubiaceae , Convolvulaceae and Malvaceae . The most species-rich tribe, Margaroniini , contains many species with larvae feeding on latex-bearing plant families like Apocynaceae and Moraceae . For most Wurthiini, nothing is known about larval food plants, only Niphopyralis Hampson with its larvae living in the nests of—and feeding on the larvae of—leafcutter ants is somewhat researched ( Allyson 1984, Mally et al. 2019).

Figures

FIGURE 30. Species diversity of Indian Spilomelinae genera.

FIGURE 31. Species diversity of Indian Spilomelinae in different biogeographic zones/zones.