Molecular diversity of populations of the Merodon ruficornis group (Diptera, Syrphidae) on the Balkan Peninsula

Genetic diversity of 11 populations of the Merodon ruficornis group (Diptera, Syrphidae) on the Balkan Peninsula was quantified using allozyme electrophoresis and nucleotide sequences of the mitochondrial cytochrome c oxidase subunit I. A total of 10 haplotypes of mtDNA were found in 22 analysed individuals. One haplotype was shared between M. loewi (from Pindos and Duba?nica Mts) and M. armipes, one confined to M. auripes (haplotype III) and M. armipes (VII) and three to M. trebevicensis (VIII, IX and X), M. ruficornis (I, II and IV) and M. loewi (V, VI and VII). Analysis of the population genetic structure parameters showed great differences among analysed species. Different levels of genetic variability suggested that a variety of biological, environmental and/or historical factors had influenced these hoverfly populations. The unweighted pair group method with arithmetic average dendrogram constructed using allozyme data suggested that M. loewi was the most divergent species in comparison with M. armipes, M. auripes, M. ruficornis and M. trebevicensis. Clear separation of the populations ((((M. armipes + M. auripes) + M. ruficornis) + M. trebevicensis) + M. loewi) was observed. The parsimony analysis of the M. ruficornis group using Merodon avidus as outgroup resulted in three equally parsimonious trees, and the strict consensus presented the following relationships ((((M. loewi + M. armipes) + (M. auripes)) + (M. trebevicensis)) + (M. ruficornis)))). The uncorrected interspecies pairwise sequence divergences ranged from 1.69% (between haplotype III of M. armipes and haplotype V of M. loewi) to 4.94% (between M. ruficornis and M. trebevicensis).     

First record of the bacterial endosymbiont Wolbachia for phytophagous hoverflies from genus Merodon (Diptera: Syrphidae)

Wolbachia is a widespread bacterial endosymbiont among arthropod species. It influences the reproduction of the host species and also mitochondrial DNA diversity. Until now there were only a few studies that detected Wolbachia infections in hoverflies (Diptera: Syrphidae), and this is the first broader study with the aim of examining the incidence of Wolbachia in the hoverfly genus Merodon. The obtained results indicate an infection rate of 96% and the presence of both Wolbachia supergroup A and B, which are characteristic for most of the infected arthropod species. Additionally, the presence of multiple Wolbachia strains in the Merodon aureus group species was detected and the mitochondrial DNA COI‐based relationships of the group are discussed in the light of infection. Finally, we discuss plant‐mediated horizontal transmission of Wolbachia strains among the studied hoverfly species.     

The effects of temperature on development of the large narcissus fly (Merodon equestris)

Eggs, larvae, pupae and adults of the large narcissus fly (Merodon equestris) were reared at a series of constant temperatures between 9–24°C. Egg development required from 37 days at 9°C to 7 days at 21.5°C. The low-temperature threshold for development was 6.7°C. Larvae reared at 1424°C were fully-grown after 18 weeks, but it took much longer for such insects to pupate, and adult flies emerged only after about 45 weeks of development. Large narcissus flies enter diapause during the larval stage and overwinter as fully-fed larvae, forming pupae in the following spring. Post-winter pupation and pupal development took from 169 days at 10°C to 36 days at 21.5°C. Of this, pupal development required from 91 days at 10°C to 19 days at 21.5°C. The low-temperature threshold for post-winter pupation and pupal development was 7.1°C, and for pupal development alone, 7.2°C. Females maintained at or below 19°C laid few eggs, whereas some females kept at or above 21.5°C laid more than 100 eggs (mean 69 ± 36). Approximately 50% of females maintained at or above 21.5°C laid less than 10 eggs during their lifetime. The mean egg-laying time was 6 to 9 days. Although temperatures at or below 19°C inhibited mating, once a female had mated, such temperatures did not prevent oviposition.     

COI barcodes for identification of Merodon hoverflies (Diptera, Syrphidae) of Lesvos Island, Greece

DNA barcoding has become a useful system for linking different biological life stages, and for identification of species within a known taxonomic framework. In this study, we generated mitochondrial DNA COI barcodes using adult specimens of all 22 species of the hoverfly genus Merodon (Diptera, Syrphidae) occurring on Lesvos island (Greece). The generated COI barcodes could well discriminate between all Merodon taxa of Lesvos, except for M. loewi and M. papillus that shared the same haplotype, despite their clear morphological differences. In addition, the barcodes revealed two cases of hitherto unknown morphologically cryptic species close to M. avidus and M. nigritarsis, respectively. Because only few successful rearings of immature stages of Merodon hoverflies are available, the larval host plant remains unknown for these phytophagous taxa. The obtained COI barcode library for the Merodon spp. of Lesvos will constitute a tool to link any unknown immature stages with already known species, and thus provide important life-history information and promise for ecological studies.