A review of the early stages and host plants of the genera Eumerus and Merodon (Diptera: Syrphidae), with new data on four species

A window on remarkable cryptic diversity of the Merodon planifacies subgroup (Diptera: Syrphidae) in the Afrotropical Region

The genus Merodon Meigen (Diptera: Syrphidae) is one of the most species-rich hoverfly genera distributed across the Palaearctic and Afrotropical regions. In the Palaearctic, the genus Merodon boasts 195 described species, while its Afrotropical region pales in comparison, with a mere 17 species documented thus far. As a result of 8 years of fieldwork conducted in the Republic of South Africa, in this paper, we present the description of 11 new species for science with a description of immature stages for 2 species, which increases the diversity of this genus in the Afrotropical region by remarkable 39%. These revelations are based on integrating morphology, molecular analysis (COI gene and 28S rRNA) and geometric morphometry. All described species belong to the Merodon planifacies subgroup, the Merodon desuturinus lineage and, within that, to the Afrotropical Merodon melanocerus group. Additionally, we provide an illustrated key to 15 species belonging to the subgroup, a detailed discussion on relevant taxonomic characters, a morphological diagnosis, a distribution map and clarification of the association between M. capi complex and host plants from the genus Merwilla.

Revisions of the clavipes and pruni species groups of the genus Merodon Meigen, 1803 (Diptera, Syrphidae)

This study focuses on the avidus-nigritarsis lineage within the genus Merodon, exploring morphological, genetic, and distributional aspects of two related assemblies within this lineage: the clavipes and pruni species groups. An integrative taxonomic approach was followed to ensure comprehensive species identification and validation, using adult morphology, wing geometric morphometrics, and genetic analysis of the mtDNA COI gene. In the clavipes group, seven species were identified, including three new species: M.aenigmaticus Vujić, Radenković & Likov, sp. nov., M.latens Vujić, Radenković & Likov, sp. nov., and M.rufofemoris Vujić, Radenković & Likov, sp. nov. In the pruni group, our revision revealed a new species, M.aequalis Vujić, Radenković & Likov, sp. nov., and the revalidation of Merodonobscurus Gil Collado, 1929, stat. rev. Merodonpallidus Macquart, 1842 is redescribed. Diagnoses, identification keys to species, and distribution maps are provided, and neotypes for Syrphusclavipes Fabricius, 1781 and Merodonquadrinotatus (Sack, 1931) are designated. Additionally, the following new synonyms are proposed: M.clavipesalbus syn. nov., M.clavipesater syn. nov., M.clavipesniger syn. nov., and M.splendens syn. nov. are junior synonyms of M.clavipes; and M.veloxarmeniacus syn. nov. and M.veloxanathema syn. nov. are junior synonyms of M.velox.

Unveiling the Mainland vs. Insular Variability of the Eumerus barbarus Species Group (Diptera: Syrphidae) in the Western Mediterranean Basin

Comprising nearly 300 described species, Eumerus Meigen, 1822, is one of the most speciose syrphid genera worldwide, and its taxonomic diversity is remarkable in the Mediterranean basin. The Eumerus barbarus (Coquebert, 1804) group consists of four species in the western Mediterranean. Although the phenotypic variability of this species group has been commented on in previous studies, it has never been contrasted with molecular data. In the present work, the morphological variation found in 300+ specimens of this species group from the western Mediterranean is explored and tested against the COI mitochondrial DNA (mtDNA). The highest phenotypic disparity was found in E. barbarus and Eumerus sulcitibius Rondani 1868. The integrative approach has not revealed cryptic diversity within the species E. barbarus but in E. sulcitibius. As a result, a new species close to E. sulcitibius was discovered, Eumerus sardus Aguado-Aranda, Ricarte & Hauser sp. n., from Sardinia, Italy. The new insular species is here described, illustrated, and discussed. A total of twenty-three haplotypes of COI mtDNA were identified amongst the analyzed Mediterranean specimens of E. barbarus, whereas two and five haplotypes were distinguished in the Iberian specimens of E. sulcitibius and Eumerus gibbosus van Steenis, Hauser & van Zuijen, 2017, respectively. Moreover, the first known barcodes of E. gibbosus and Eumerus schmideggeri van Steenis, Hauser & van Zuijen, 2017 were obtained, and the distribution ranges of all species are mapped. An updated dichotomous key to the males of the E. barbarus group from the western Mediterranean is provided.

The Extraordinary Diversity of Merodon avidus Complex (Diptera: Syrphidae)-Adding New Areas, New Species and a New Molecular Marker

In this paper, the Merodon avidus (Diptera, Syrphidae) species complex was revised, whereupon we discovered and described four new species for science: Merodon atroavidus Vujić, Radenković et Likov sp. nov., M. magnus Vujić, Kočiš Tubić et Ačanski sp. nov., M. nigroscutum Vujić, Radenković et Likov sp. nov. and M. pseudomoenium Vujić, Kočiš Tubić et Ačanski sp. nov. An integrative taxonomy approach was used to delimit species boundaries. Two molecular markers (the mitochondrial COI gene and nuclear 28S rRNA gene-newly analysed marker for the complex) and geometric morphometry of the wing shape, together with morphological data and distribution, successfully separated all species from the complex. The morphological variability of the analysed species is described and discussed and an illustrated diagnostic key for typical morpho-forms of species from the M. avidus complex is presented. A distribution map of all investigated species from the complex is provided. The level of endemicity of the M. avidus complex was discussed.

On the immature stages of some Merodontini hoverflies (Diptera: Syrphidae) from Europe and Africa

The genera Eumerus and Merodon (Syrphidae: Merodontini) form together the most speciose grouping of hoverflies in the Palaearctic Region. However, little is known about the morphology and biology of their larvae. The few larvae of Eumerus and Merodon that have been uncovered are phytophagous in underground organs of plants (some Eumerus and all Merodon) or saprophagous in a variety of plants' parts (the reminder of Eumerus). In this study, the second larval stage (L2) of Eumerus lyneborgi Ricarte & Hauser, 2020 and both the larva (L2) and puparium of Merodon constans (Rossi, 1794) are described for the first time. Larvae of E. lyneborgi were found in a decaying stem of Cyphostemma juttae (Dinter & Gilg) Desc., 1960 (Vitaceae) in Namibia (Africa), while larvae of M. constans were collected in bulbs of Leucojum vernum Linnaeus, 1753, (Amaryllidaceae) in France (Europe). Morphology of the immature forms was studied by observation and imaging with stereomicroscopy and scanning electron microscopy. The head skeleton of E. lyneborgi larvae was found to be of the filter feeding type, i.e., in accordance with a saprophagous trophic regime, while that of M. constans was typically phytophagous. Variability in certain characters of the M. constans early stages is described and discussed in relation to the adult form and molecular information published in literature. An updated identification key to all known third larval stages/puparia of Merodon is provided.

Are Appearances Deceiving? Morpho-Genetic Complexity of the Eumerus tricolor Group (Diptera: Syrphidae) in Europe, with a Focus on the Iberian Peninsula

Eumerus Meigen, 1822 is one of the largest Syrphidae genera in the Palaearctic Region, with the highest levels of taxonomic diversity found in the Eumerus tricolor species group. Despite its high diversity, the interspecific levels of morphological variability can be low. Additionally, some species may show certain levels of intraspecific variability. Hence, species delimitation may become challenging. In this work, we assessed the diversity of the E. tricolor group in the Iberian Peninsula through an integrative analysis of nomenclature, morphology and the 5' (COI-5') and 3' (COI-3') end regions of the Cytochrome c oxidase subunit I gene. Two new species, Eumerus ancylostylus Aguado-Aranda & Ricarte sp. n. and Eumerus petrarum Aguado-Aranda, Nedeljković & Ricarte sp. n., were described, and their intra- and interspecific variations discussed. In addition, the first barcodes of Iberian members of the E. tricolor group were obtained, and the distribution ranges of all species were mapped within the study area. The systematic position of the new species is discussed based on the resulting COI-based trees. The male genitalia of Eumerus hispanicus van der Goot, 1966 and Eumerus bayardi Séguy, 1961 were studied and illustrated. A lectotype was designated for Eumerus lateralis (Zetterstedt, 1819). An updated dichotomous key for all known European species of the E. tricolor group is provided. The egg of E. petrarum sp. n. is also described.

Combined stereomicroscope and SEM disentangle the fine morphology of the undescribed larva and puparium of the hoverfly Milesia crabroniformis (Fabricius, 1775) (Diptera: Syrphidae)

With over 80 species, Milesia Latreille, 1804 is a hoverfly genus (Diptera: Syrphidae) found in all continents except for Australia and the Antarctica. However, little is known about its life cycle and biology. The three Milesia species for which early stages are known have saproxylic larvae, suggesting that the larvae of all other Milesia species are also saproxylic. The early stages of the three Milesia species occurring in Europe are undescribed. Milesia crabroniformis (Fabricius, 1775), a mimic of the hornet Vespa crabro Linnaeus, 1758, is the largest hoverfly in Europe and is listed as Least Concern in the IUCN European Red List of Hoverflies. We here report the first early stages of Milesia ever found in Europe, describing them and their breeding sites. Larvae of M. crabroniformis were collected in water-filled tree holes of live chestnut trees (Castanea sativa Mill.) in Málaga, Southern Spain in 2020-2021. Various studies based on stereomicroscope and scanning electron microscopy (SEM) techniques have proven useful in diagnosing hoverfly early stages by observation of their fine morphology. Thus, these techniques were also used here to characterize the second (L2) and third (L3) stage larvae of M. crabroniformis, as well as the puparium. A Leica M205C binocular stereomicroscope and a Jeol JSM-ITH500HR SEM were used. The head skeleton and chaetotaxy of the L3 larva were described and illustrated. Adjustments to the diagnosis of the larvae of Milesia are proposed based on the number of hooks from the primary row of the main group of hooks. The new early stages are compared with those of other Milesia hoverflies, as well as with those of the sister group Spilomyia Meigen, 1803. The knowledge of the larval biology and breeding sites of saproxylic insects is useful for implementing forest management measures and species' conservation programs.

Morphological characteristics and biological cycle of the hoverfly Eristalinus arvorum (Fabricius, 1787) (Diptera, Syrphidae)

The hoverfly Eristalinus arvorum (Fabricius, 1787) (Diptera: Syrphidae), which belongs to the tribe Eristalini, is well known as a pollinating agent for crops and flowering plants in agricultural and natural ecosystems. Large quantity, wide distribution and their ecological function of the hoverfly E. arvorum make them an appropriate candidate for use as pollinators and environmental indicator species. However, little information has been known on the morphology and the biological cycle of the hoverfly. In this study, feeding experiments under artificial climate chamber and morphological qualitative and quantitative observations were carried out to study the morphology and the biological cycle of the hoverfly E. arvorum. The morphology of eggs, larvae, pupae, and adults of E. arvorum were described in detail for the first time. A complete generation of E. arvorum lasts about 30.12 ± 0.14 days, and there is no significant difference in body length between males (10.27 ± 0.29 mm) and females (11.16 ± 0.45 mm). The most noteworthy morphological features of E. arvorum are the stripes on the compound eyes, the mesonotum, and the abdomen of adults, the chorionic structure consisting of fusiform units on the egg's surface, and the anterior spiracles and pupal spiracles of the pupae. Thus, the detailed description based on morphology and life history will provide the basis for the identification, biodiversity conservation and artificial breeding of the hoverfly E. arvorum.

Integrative taxonomy of the Merodon aberrans (Diptera, Syrphidae) species group: distribution patterns and description of three new species

In this paper, we revise the Merodon aberrans species group of the genus Merodon Meigen, 1803 (Diptera: Syrphidae), providing morphological diagnoses and descriptions, molecular data for three species, as well as an illustrated key and a discussion of the different taxonomic characters used. We also discuss distribution patterns for this species group. The results revealed that the M. aberrans group is composed of five described species (M. aberrans Egger, 1860, M. brevis Paramonov, 1926, M. flavitibius Paramonov, 1926, M. hamifer Sack, 1913, and M. warnckei Hurkmans, 1993) and three new ones, namely M. hermonensis Vujić, Radenković et Likov sp. nov., M. petiolatus Vujić, Radenković et Rojo sp. nov., and M. retectus Vujić, Radenković et Likov sp. nov. Following a detailed study of the type material in different entomological collections, the status of several species is revised, one new synonym is proposed (subspecies M. aberrans isperensis Hurkmans, 1993 as junior synonym of M. flavitibius), lectotypes are designated for M. kneri Mik, 1867 and M. flavitibius, and paralectotypes are designated for M. hamifer and M. flavitibius. Seven out of eight species from the M. aberrans group are distributed in the Asian continent, namely all Caucasian countries, Turkey and Iran, confirming the notion about high diversity of Merodon species in these regions, but also highlighting the need for a systematic faunistic research.

Characterization of preimaginal developmental stages of two cryptic South African species of the Merodon planifacies complex (Diptera: Syrphidae: Eristalinae: Merodontini), with differentiation through morphometry analysis

Merodon capi Vujić et Radenković, 2020 and Merodon roni Radenković et Vujić, 2020 are two cryptic species belonging to the Merodon planifacies Bezzi, 1915 species complex that have recently been described, with the differences between them being revealed by molecular and geometric morphometry studies of adult specimens. In the present study, the preimaginal morphology of both species is described and displayed, with the material used corresponding to samples taken from bulbs of Merwilla plumbea (Lindl.) Speta plants at two locations in KwaZulu-Natal province (South Africa). The preimaginal stages were compared, looking for morphological evidence supporting species divergence. Linear and geometric morphometric analyses of the larval posterior respiratory process were conducted for the first time and the results of these analyses support the separation of the two taxa. Information about the life cycle and the relation with the host plant is also provided. In addition, we carried out a preliminary study of the adult feeding requirements of the species, based on the description of the mouthparts and an analysis of the pollen present in the gut and on the integument of adults. The results of the study supports a close relationship between the preimaginal stages and plant species of the Hyacinthaceae family.

The role of soils on pollination and seed dispersal

Ongoing environmental changes are affecting physical, chemical and biological soil components. Evidence of impacts of soil changes on pollinators' and seed dispersers' behaviour, fitness and density is scarce, but growing. Here, we reviewed information on such impacts and on a number of mechanisms that may explain its propagation, taking into account the full range of resources required by the large and diverse number of species of these two important functional groups. We show that while there is substantial evidence on the effects of soil nitrogen enrichment and changes in soil water content on the quality and quantity of floral and fruit resources, little is known on the effects of changes of other soil properties (e.g. soil pH, soil structure, other nutrients). Also, the few studies showing correlations between soil changes and pollinator and seed disperser foraging behaviour or fitness do not clearly identify the mechanisms that explain such correlation. Finally, most studies (including those with nitrogen and water) are local and limited to a small number of species, and it remains unclear how variable such effects are across time and geographical regions, and the strength of interactive effects between soil properties. Increasing research on this topic, taking into consideration how impacts propagate through species interaction networks, will provide essential information to predict impacts of ongoing environmental changes and help guide conservation plans that aim to minimize impacts on ecosystem functioning. This article is part of the theme issue 'The role of soils in delivering Nature's Contributions to People'.

Taxonomic complexity in the genus Merodon Meigen, 1803 (Diptera, Syrphidae)

The genus Merodon Meigen, 1803 is distributed across the Palaearctic and Afrotropical Regions. The present work summarizes the knowledge from recent taxonomic and systematic revisions and includes an identification key for the five monophyletic lineages (namely albifrons, aureus, avidus-nigritarsis, desuturinus and natans), 24 species groups, two species subgroups and 10 unplaced species, along with diagnosis and illustrations. A list of 234 taxa, including 194 described and 40 undescribed species, is appended. Most of the species are distributed in the Palaearctic (209 taxa, 181 described), while 27 species (14 described) are known from the Afrotropical Region. Three lineages (aureus, desuturinus and natans) are present in the Afrotropical Region, as well as in the Palaearctic. The Afrotropical melanocerus species group of the desuturinus lineage and the bombiformis species group of the aureus lineage are endemic to the Afrotropical Region, and all other species groups belong to the Palaearctic fauna. The albifrons lineage contains six species groups (albifrons, constans, equestris, geniculatus, ruficornis and rufus) and two unplaced taxa. The aureus lineage includes five species groups (aureus, bombiformis, funestus, nanus and spinitarsis). The avidus-nigritarsis lineage is divided into 10 species groups (aberrans, aurifer, avidus, clavipes, fulcratus, italicus, nigritarsis, pruni, serrulatus and tarsatus) and eight unplaced taxa. The desuturinus lineage contains two species groups: the Afrotropical melanocerus group, with the melanocerus and planifacies subgroups plus the species M. cuthbertsoni Curran, 1939, and the Palaearctic murorum species group. The natans lineage consists of the natans species group plus the species M. segetum Fabricius, 1794.

Morphological, Genetic and Biological Evidences to Understand Meromacrus Rondani Diversity: New Species and Early Stages (Diptera: Syrphidae)

Simple Summary

Hoverflies or flower flies, technically known as syrphids, are insects providing important ecosystem services. They are used as indicators of biodiversity and habitat quality, as well as models for evolution studies. The better syrphids are known the better can be used with different aims. Meromacrus is a genus of showy syrphids that pollinate plants and decompose organic materials in the Americas. However, their classification and biology are still being investigated. In this study, morphology and DNA were used in combination to define species concepts. Two species new to science were discovered, one from Mexico and the other from Peru. The immatures (e.g., larvae or pupae) and breeding sites of these species were also described, with the larva of the Peruvian species happening to be the first ever found in a rotting cactus. To assist those working with immatures, we provide here an identification key to Meromacrus species. Our work represents the starting point for a modern revision of the Meromacrus classification and provides data that, in future, can be used to interpret evolutionary relationships within this genus.

Abstract

Meromacrus is a genus of conspicuous syrphids with saprophagous larvae, ranging from the southern United States to Argentina and Chile. However, this genus is in need of a taxonomic revision. Adults reared from larvae collected in Mexico and Peru, and other material available at different institutional collections were examined. Meromacrus cactorum sp. nov., from Peru, Meromacrus yucatense sp. nov., from Mexico, their puparia and breeding sites were described. A key to Meromacrus puparia is provided. The holotypes of Meromacrus canusium, Meromacrus gloriosus, Meromacrus laconicus and Meromacrus melmoth were also examined. The name Meromacrus draco is proposed as a junior synonym of M. gloriosus. Larvae of M. cactorum sp. nov. were found in decaying columnar cacti in Peru, while those of M. yucatense sp. nov. in a rot-hole of a Ceiba pentandra stump. Obtained results on both taxonomy and biology of these species serve as a first step towards a revision of the entire genus.

Revision of the Merodon serrulatus group (Diptera, Syrphidae)

The phytophagous hoverfly genus Merodon Meigen, 1803 (Diptera, Syrphidae), which comprises more than 160 species distributed in Palaearctic and Afrotropical regions, can be differentiated into multiple groups of species that harbor high levels of hidden diversity. In this work, the serrulatus species group of Merodon is revised, providing an illustrated key to species, a detailed discussion on the taxonomic characters and a morphological diagnosis, including also the first data about the preimaginal morphology of this species group. The study includes characteristics of the 13 species of the M. serrulatus group, along with the available distributional data. Moreover, descriptions are provided for seven new species, namely M. defectus Vujić, Likov & Radenković sp. nov., M. disjunctus Vujić, Likov & Radenković sp. nov., M. medium Vujić, Likov & Radenković sp. nov., M. nigrocapillatus Vujić, Likov & Radenković sp. nov., M. nigropunctum Vujić, Likov & Radenković sp. nov., M. opacus Vujić, Likov & Radenković sp. nov., and M. trianguloculus Vujić, Likov & Radenković sp. nov. In addition, the taxa M. serrulatus (Wiedemann in Meigen, 1822), M. bequaerti Hurkmans, 1993, M. hirsutus Sack, 1913, M. kawamurae Matsumura, 1916, M. sacki (Paramonov, 1936) and M. sophron Hurkmans, 1993 are redefined and redescribed. Following a detailed study of the type material sourced from different entomological collections, the status of all available taxa related to M. serrulatus is revised and a new synonymy is proposed: M. tener Sack, 1913 syn. nov. (junior synonym of M. serrulatus). The identity of M. trizonus (Szilády, 1940) could not be assessed as the type specimens are lost. Thus, the name M. trizonus is considered as nomen dubium. The monophyly and composition of this species group are assessed through Maximum Parsimony and Maximum Likelihood analyses of the mitochondrial COI and nuclear 28S rRNA gene sequences.

Conflict and congruence between morphological and molecular data: revision of the Merodon constans group (Diptera : Syrphidae)

We revise the Merodon constans species group of the genus Merodon Meigen, 1803 (Diptera: Syrphidae), provide morphological diagnosesand descriptions, as well as an illustrated key and a discussion on the different taxonomic characters used. In total, 15 species were studied, their geographic distributions are presented on maps, and nine new species are described. Two species are redefined and neotypes are designated, lectotypes are designated for five species, and onespeciesis reinstated as valid. Following a detailed study of type material in different entomological collections, the status of several species is revised and three new synonymies are proposed. The M. constans species group was resolved as being monophyletic within the M. albifrons lineage based on molecular analyses using COI and 28S rRNA gene sequences. Three species morphologically similar to M. constans (Rossi, 1794) but occurring outside its distributional rangewere supported as being valid and distinct species on the basis of molecular data, but they were not distinguishable based on morphological characters. By contrast, continental populations of M. analis Meigen, 1822 could not be separated from Mediterranean M. constans based on differences in COI or 28S rRNA genes. The same molecular markers could not discriminate between two other species pairs. We conclude that these molecular markers only partially resolve species within the M. constans group. Geometric morphometry of wing shape successfully separated M. analis and M. constans, as well as M. spineus Vujić, Šašić Zorić & Likov, sp. nov. in both species and population analyses.

Close relatives of Mediterranean endemo-relict hoverflies (Diptera, Syrphidae) in South Africa: Morphological and molecular evidence in the Merodon melanocerus subgroup

An ongoing study of the genus Merodon Meigen, 1803 in the Republic of South Africa (RSA) has revealed the existence of new species related to M. melanocerus Bezzi, 1915. The M. melanocerus subgroup belongs to the Afrotropical lineage of the M. desuturinus group. Revision of all available material from museums and detailed analyses of newly -collected specimens from our own expeditions to RSA resulted in delimitation of five species: M. capensis Hurkmans sp. n., M. commutabilis Radenković et Vujić sp. n., M. drakonis Vujić et Radenković sp. n., M. flavocerus Hurkmans sp. n. and M. melanocerus. In addition to classical morphological characters, sequences of the mitochondrial COI gene are provided for four related taxa. Results of molecular phylogenetic analyses supports monophyly of the M. desuturinus group and confirmed delimitation between species. Links between Palaearctic and Afrotropical faunas of this group, as well as possible evolutionary paths, are discussed. Based on phylogenetic analyses, four lineages (putative subgenera) have been recognized within the genus Merodon; besides the three previously established ones, albifrons+desuturinus, aureus (sensu lato) and avidus-nigritarsis, one new lineage named natans is distinguished.