Melolonthini
Creators: name: Allsopp, Peter G.
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Scarabaeidae

description: Melolonthini, or Melolonthini and Leucophilini?
A conventional classification of the Australian Melolonthinae (Britton 1957, 1978, 1990; Cassis & Weir 1992; Weir et al. 2019; this paper) (Melolonthini sensu Britton 1978) places a group of 17 genera and 123 species, dominated by Lepidiota Kirby, 1828, Antitrogus Burmeister, 1855, and Rhopaea Erichson, 1847, in the Melolonthini, but without reference to any subtribes. Weir et al. (2019) characterised the tribe from other Australian melolonthines by: metatibiae with two spurs placed below the tarsal articulation; tarsal claws almost always with a tooth on the concave side; labrum separate from the clypeus and located below it; antennae with 9 or 10 antennomeres and with a 3–8 lamellate club; body surface not metallic. The group contains some economically important species as pests of pastures and crops, especially sugarcane (Allsopp 2010).
However, the monophyly of the Melolonthinae and the status of its tribes and subtribes has been questioned (Ahrens 2006; Coca-Abia 2007), especially with the advent of DNA technologies (Smith et al. 2006; Song & Zhang 2018; Ayivi et al. 2021). A radical alternative classification has been that of Lacroix (2021a). He, albeit with little commentary, split the subfamily in four and elevated these to family level (Hopliidae, Melolonthidae, Sericidae, Chasmatopteridae), whilst elevating previous tribes and subtribes to subfamily or tribe status. Other alternative classifications have seen subtribes of the Melolonthini (Smith 2006; Bouchard et al. 2011) elevated to tribes (Lacroix 2010, 2021b; Bezděk 2016; Evans & Smith 2020).
Lacroix (2010) moved some of the African genera formerly in Melolonthini to the Leucophilini, and Bezděk (2016) followed this for the Palaearctic Lepidiota species. Recently, Lacroix (2021b) placed the Australian Lepidiota species, Holorhopaea Britton, 1978 (1 species), and Nanorhopaea Britton, 1978 (1 species) in the Leucophilini, with the other Australian genera (presumably including Alepida Allsopp, 2018 and the Fijian-Solomon Islands Xenotrogus Britton, 1978) remaining in the Melolonthini (Melolonthini sensu Lacroix 2021b). Lacroix (2021b) characterised the Leucophilini as having antennal clubs of three lamellae that are similar in both sexes and large metepisterna, whilst the Melolonthini sensu Lacroix 2021b have antennal clubs of more than three lamellae with pronounced sexual dimorphism and the dorsal surface of the body with scales and/or setae.
Australian Lepidiota species (as restricted with the removal of Alepida species (Allsopp 2018) and those earlier in this paper) are obviously different from other Australian Melolonthini sensu Britton 1978. Weir et al. (2019) showed this clearly in their key to genera, where Lepidiota is separated from other genera in couplet 1. Prominent identifiers are a combination of: dorsal surface with small, white scales contained or nearly contained within their punctures, without longer white or brown, adpressed or erect setae; antennal club of three lamellae with no obvious sexual dimorphism (Allsopp 1990b gives an example); females often found in collections and adults may feed; and males of most species with parameres asymmetrical and often bizarrely shaped (see figures in Britton 1978). This was reinforced in a cladistic analysis of a sample of Melolonthini sensu Britton 1978 from eastern Australia using adult and larval morphological and ecological characters (Allsopp & Lambkin 2006) where the 10 Lepidiota species that were considered formed a clade separate from species in Antitrogus, Rhopaea, Dermolepida Arrow, 1941 and Alepida.
The genera assigned to Melolonthini sensu Lacroix 2021b have: setae (Figs 2–6, 14–18), not scales, on the dorsal surface; antennal clubs with 3–8 lamellae and, where known, females have much smaller clubs than males (Britton 1978: fig. 150; Allsopp 1990b); females of most species are rare in collections, probably fly little after emergence and are not attracted to light, and adults of both sexes do not feed (the exception are Dermolepida species); and males have parameres that are symmetrical or nearly so.
Lacroix’s (2021b) placement of Nanorhopaea and Holorhopaea in the Leucophilini is problematic. Males of the two species have antennal clubs of three lamellae, as do Lepidiota species (and some Melolonthini sensu Lacroix 2021b), but they are of medium length (Weir et al. 2019: fig. 142). Females are not known (Britton 1978), so sexual dimorphism in the antennae cannot be assessed. The dorsal surface of males does not have the small, white scales characteristic of Lepidiota, but have either recumbent, tapered, finely pointed setae or long, semierect setae (Britton 1978: fig. 270A–B; Weir et al. 2019: figs. 31.142, 31.145; Fig. 6). The aedeagi of the two species have symmetrical parameres (Britton 1978: figs. 15–19), unlike the often-asymmetrical parameres of Lepidiota species. All three characters point to a closer relationship with the Melolonthini sensu Lacroix 2021b than with the Leucophilini.
Lacroix (2021b) thought that both the Leucopholini and the Melolonthini sensu Lacroix 2021b entered Australia from the north from the Pliocene onwards. He considered the Leucopholini a fairly recent group, forming in the Ethiopian-Malagasy-Indian block, before the complete separation of these three blocks but after the separation of the South America-Antarctic-Australia blocks. From there they disseminated to West Africa and east to as far as Australia and Solomon Islands, crossing Wallace’s Line. Lacroix (2021b) considered the Melolonthini sensu Lacroix 2021b a recent group appearing in north-eastern and southern Palaearctic regions after the separation of all blocks. Diffusion then occurred to give a current distribution in North America, Palaearctic, Oriental and Australian regions, with few in the Afrotropical Region and absent from the southern Neotropical region and Madagascar. My hypothesis (Allsopp 1995), based on patterns of distribution of the Australian species, is that Lepidiota is a post-Pliocene invader from the north, whilst the remaining genera, especially Rhopaea and Antitrogus, are older elements.
However, Lacroix’s (2010, 2021a, 2021b) split is far from being accepted. Within the Melolonthini sensu Britton 1978, Matsumoto (2010) analysed the characters of 25 Palaearctic and Oriental species from the two lineages and found it impossible to assign all the genera to either of the lineages. Prokofiev (2016) pointed out inconsistencies in the number of lamellae in antennal clubs among Lepidiota species from New Guinea and Solomon Islands, as well as in the presence/absence of scales and in the placement of genera such as Engertia Dalla Torre, 1912. He commented that perhaps Britton (1978) was correct in considering representatives of both groups as a single tribe. Obviously, there is a strong need for a comprehensive analysis of status and defining characters of tribes and subtribes of the Melolonthinae across all regions, and DNA analysis might give useful characters This would then give insights into the past biogeography and dissemination of the family.
description: Published as part of Allsopp, Peter G., 2022, Australian Melolonthini (Coleoptera: Scarabaeidae: Melolonthinae): reclassification of eight species to Antitrogus Burmeister, 1855 and Barryfilius new genus, pp. 513-545 in Zootaxa 5213 (5) on pages 535-536, DOI: 10.11646/zootaxa.5213.5.3, http://zenodo.org/record/7381670