Megaselia Scalaris Research Articles

Heterochronic shifts in germband movements contribute to the rapid embryonic development of the coffin fly Megaselia scalaris

The coffin fly, Megaselia scalaris, is a species of medical and forensic importance and is increasingly being used for the study of genetics. Postmortem interval can be estimated based on the life stage of M. scalaris recovered from corpses, therefore many studies have addressed the duration of each life stage. These studies demonstrate that embryogenesis completes significantly faster in M. scalaris than in the congener Megaselia abdita and faster even than the 24 h needed for Drosophila melanogaster embryogenesis. However, until now it has been unclear if this increased speed is achieved by reducing developmental time across all embryonic stages or by the acceleration of individual stages and processes. Here I use time-lapse imaging to create a staging scheme for M. scalaris embryogenesis. Comparison of stages between D. melanogaster and both Megaselia species reveals that heterochronic shifts, simultaneous morphogenetic movements and compression of individual stages all contribute to the rapid development of M. scalaris.

Developmental rate, size, and sexual dimorphism of Megaselia scalaris (Loew) (Diptera: Phoridae): its possible implications in forensic entomology.

Cosmopolitan scuttle fly, Megaselia scalaris (Loew) (Diptera: Phoridae) is one of the commonest forensic species recorded colonizing human corpse indoors and in concealed environment. The occurrence of this species in such environments provides a higher evidential value to assist estimation of postmortem interval (PMI) compared to other forensically important dipterans. However, developmental and size data of M. scalaris are still lacking and they are derived from a limited range of thermal values. The objective of this study is to develop the growth model of M. scalaris by emphasizing the size range of larvae and puparia at different constant temperatures. This species was reared in six replicates at eight varying constant temperatures ranging from 23 to 36°C and cow's liver was provided as food source. Larvae and puparia were sampled at set time intervals and measured by their length and weight. Because interpretation of forensic entomological evidence is subject to application of different techniques, development of M. scalaris is expressed herein by using developmental table, length/morphological stage diagrams and linear/nonlinear estimation methods. From the findings, it is very important to highlight that sexual dimorphism of M. scalaris during post feeding larva and pupa stage could be observed based on size and developmental periods. Mean length and weight ratios of male to female puparia are approximately 0.8 and 0.3-0.5, respectively, indicating sexual dimorphism of this species. Developmental period in female are 4.0-11.4h (post feeding larval stage), 3.7-24.0h (pupal stage), and 3.0-20.1h (total developmental period) longer in male. Due to this dimorphism, PMI estimation using M. scalaris post feeding larva or puparium specimens must be carried out carefully by to avoid inaccuracy and misinterpretation.

The complete mitochondrial genome of the scuttle fly, Megaselia scalaris (Diptera: Phoridae)

More than 1400 scuttle flies species in worldwide comprise the Megaselia genus, the largest genus in the family Phoridae. The complete mitochondrial genome of Megaselia scalaris, a medically important entomology was sequenced for the first time. The 15,599 bp circular genome contains the 37 genes found in a typical Metazoan genome: 13 protein-coding genes, 22 transfer RNA genes and 2 ribosomal RNA genes. The mitochondrial genome also contains one non-coding A + T-rich region. The arrangement of the genes was identical with other insect. Each of the base composition on heavy strand was as follows A: 38.87%, G: 13.74%, C: 9.46%, T: 37.93% and the A + T content 76.80%. The mitochondrial genome of M. scalaris presented may be valuable for determining phylogenetic relationships within the order Diptera and especially for the family Phoridae. These sequences could also be used to select reliable molecular markers for species identification in forensic entomology.

Megaselia scalaris (Diptera: Phoridae) can live on ripe bananas--a potential health hazard?

Identification of larvae that inest bananas and investigating its habits. Laboratory based study. Department of Parasitology, Faculty of Medicine, University of Colombo. Bananas brought to the department with a query of maggot infestation were examined and the presence of maggots was confirmed. Maggots were allowed to develop into adults. The larvae and the flies were identified using standard keys. Megaselia scalaris was identified, the larvae of which infest ripe bananas. Three generations of M scalaris were reared using ripe bananas as the only source of food. Two other banana specimens yielded larvae that eventually grew into adult flies of Bactrocera species. In addition to Bactrocera spp. larvae of which are known pests in bananas, M scalaris larvae were detected as pests for the first time. We demonstrated that M scalaris can complete its life-cycle depending on ripe bananas as the only source of food. The vast consumption of bananas and the potential of M scalaris to cause intestinal and wound myiasis in humans make these findings medically important.

Pupal age estimation of forensically important Megaselia scalaris (Loew) (Diptera: Phoridae)

In addition to causing myiasis in humans and animals, Megaselia scalaris (Loew) has been reported as a forensically important fly. The determination of a minimum postmortem interval (PMI) often relies on the determination of the age of the larvae and pupae. The pupal stage represents about 50% of the immature development time and the pupal age may therefore serve as an important tool in entomological minimum PMI estimation. The present study focuses on the key developmental processes during metamorphosis of M. scalaris pupae at different constant temperatures (18, 21, 24, 27, 30, 33 and 36°C). The average minimum duration of development from prepupa to adult emergence was inversely related to temperature, ranging from 170.65±1.39h at 33°C to 608.80±13.26h at 18°C. The pupa did not develop at 36°C. Some morphological features that changed during development within the puparium could be used as age markers. According to these changes, the pupal stage of M. scalaris was divided into 10 stages which could be used for both sexes.

A staging scheme for the development of the scuttle fly Megaselia abdita.

Model organisms, such as Drosophila melanogaster, provide powerful experimental tools for the study of development. However, approaches using model systems need to be complemented by comparative studies for us to gain a deeper understanding of the functional properties and evolution of developmental processes. New model organisms need to be established to enable such comparative work. The establishment of new model system requires a detailed description of its life cycle and development. The resulting staging scheme is essential for providing morphological context for molecular studies, and allows us to homologise developmental processes between species. In this paper, we provide a staging scheme and morphological characterisation of the life cycle for an emerging non-drosophilid dipteran model system: the scuttle fly Megaselia abdita. We pay particular attention to early embryogenesis (cleavage and blastoderm stages up to gastrulation), the formation and retraction of extraembryonic tissues, and the determination and formation of germ (pole) cells. Despite the large evolutionary distance between the two species (approximately 150 million years), we find that M. abdita development is remarkably similar to D. melanogaster in terms of developmental landmarks and their relative timing.

New records of scuttle flies (Diptera: Phoridae) from caves in the Bakony Mountains, Hungary

New records of scuttle flies (Diptera: Phoridae) from caves in the Bakony Mountains, Hungary

Scuttle Flies (Diptera: Phoridae) Reared from Fungi in Benin

ABSTRACT Ten species of Phoridae reared from fungi in Benin are reported, including the descriptions of the following: Megaselia cakpoae Disney, sp. n., Megaselia fuscilobulorum Disney, sp. n., Megaselia kurinai Disney, sp. n. and Megaselia tedersooi Disney, sp. n. Megaselia termitomyca Disney, 1989 is synonymised with Megaselia labiata Borgmeier, 1967.

Evolution of the Sex-lethal Gene in Insects and Origin of the Sex-Determination System in Drosophila

Sex-lethal (Sxl) functions as the switch gene for sex-determination in Drosophila melanogaster by engaging a regulatory cascade. Thus far the origin and evolution of both the regulatory system and SXL protein's sex-determination function have remained largely unknown. In this study, we explore systematically the Sxl homologs in a wide range of insects, including the 12 sequenced Drosophila species, medfly, blowflies, housefly, Megaselia scalaris, mosquitoes, butterfly, beetle, honeybee, ant, and aphid. We find that both the male-specific and embryo-specific exons exist in all Drosophila species. The homologous male-specific exon is also present in Scaptodrosophila lebanonensis, but it does not have in-frame stop codons, suggesting the exon's functional divergence between Drosophila and Scaptodrosophila after acquiring it in their common ancestor. Two motifs closely related to the exons' functions, the SXL binding site poly(U) and the transcription-activating motif TAGteam, surprisingly exhibit broader phylogenetic distributions than the exons. Some previously unknown motifs that are restricted to or more abundant in Drosophila and S. lebanonensis than in other insects are also identified. Finally, phylogenetic analysis suggests that the SXL's novel sex-determination function in Drosophila is more likely attributed to the changes in the N- and C-termini rather than in the RNA-binding region. Thus, our results provide a clearer picture of the phylogeny of the Sxl's cis-regulatory elements and protein sequence changes, and so lead to a better understanding of the origin of sex-determination in Drosophila and also raise some new questions regarding the evolution of Sxl.

Multiple colonization of a cadaver by insects in an indoor environment: first record of Fannia trimaculata (Diptera: Fanniidae) and Peckia (Peckia) chrysostoma (Sarcophagidae) as colonizers of a human corpse

We describe here a case of multiple colonization of a male cadaver found indoors in the municipality of Jaboatao dos Guararapes, Brazil. The body was colonized by six species of Diptera: Chrysomya albiceps, Chrysomya megacephala, Chrysomya putoria (Calliphoridae), Megaselia scalaris (Phoridae), Fannia trimaculata (Fanniidae), and Peckia (Peckia) chrysostoma (Sarcophagidae). The most abundant species were C. albiceps (65.0% of all emerged adults) and C. megacephala (18.6%). The case illustrates the ability of six insect species to simultaneously colonize a corpse in an indoor environment and represents the first collaboration between the forensic police and entomologists in Northeastern Brazil. We provide here the first record of two species, F. trimaculata and Peckia (P.) chrysostoma colonizing a human cadaver. We also report the first case of cadaver colonization by C. putoria and M. scalaris in Northeastern Brazil. Information on the development time of two species, C. albiceps and C. megacephala, were used to discuss the estimation of the post-mortem interval. Considering that the region harbors the highest rates of homicide in Brazil, implications of these findings for the consolidation of forensic entomology in the region are discussed.

An unusually rich scuttle fly fauna (Diptera, Phoridae) from north of the Arctic Circle in the Kola Peninsula, N. W. Russia

64 species of Phoridae, in 6 genera, are reported from the Kola Peninsula, north of the Arctic Circle. The new species Megaselia elenae and Megaselia kozlovi are described. 33 species of Megaselia, only known from females, are given code numbers. Keys to the species of all the females of Megaselia and Phora are provided; and also a key to the males European Megaselia species with a notopleural cleft.

Effects of disturbances on scuttle flies (Diptera: Phoridae) in Pine Forests

I investigated the ecological consequences of disturbances (anthropogenic and natural) on the scuttle fly communities in four large Pine Forests in Poland. I used data on 17,547 male individuals representing 183 species. Communities found in pine plantations (established in clear-cut areas) and in differently treated post-windstorm (with windthrow logs being left or removed) were less diverse than those found in old-growth forest. The communities recorded in the same habitat types in different forest complexes (ca. 300 km apart) were found to display greater similarity than those recorded on adjacent plots in a given forest (ca. 1 km apart), but covering different habitats. The species-specific preference for habitats after disturbances (clear-cuts and post-windstorm areas) was highly correlated between the forests. The abundance of the species with saprophagous larvae was distinctly higher in the disturbed areas than in the old-growth stands. Also, the body length of the scuttle flies was significantly related to their preference for disturbed or undisturbed habitats: smaller species preferred clear-cuts and post-windstorm areas, whereas larger species were related to intact stands.

Water balance characteristics of pupae developing in different size maggot masses from six species of forensically important flies

The impact of maggot mass size on body water content, net transpiration rate, and dehydration tolerance of fly pupae was examined in six species of necrophagous flies. Species that spent more time on food as larvae, produced pupae with high body water contents. Dehydration tolerance limits of pupae were modest, matching the moisture-rich conditions of decaying carrion for larvae. Protophormia terraenovae pupariates on food as it dries, and this was reflected by pupae having the highest body water content and lowest net transpiration rate. Megaselia scalaris featured the lowest body water content and highest dehydration tolerance, implying that this species is arid-suited, which matches its ability to feed and colonize on post-decay carrion. Lucilia illustris was the most sensitive to larval overcrowding, resulting in a dramatic decrease in pupal size, early dispersal from food, fed less and had fast net transpiration rates. By contrast, Lucilia sericata was the most resistant, by showing no pupal size decrease and no change in net transpiration rate. Other species were between these extremes, requiring larger maggot mass sizes to produce the effect of decreasing pupal size and increasing net transpiration rate. We conclude: (1) the pupa’s response to overcrowding and water balance profile are species-specific, varying according to pupal size and net transpiration rate as independent characteristics; (2) water balance profile of the pupae reflects the behavior and microhabitat of the larva; and (3) danger of lethal desiccation to smaller-sized pupae is circumvented by a faster developmental rate rather than enhanced water conservation.

Insect Arrival Pattern and Succession on Buried Carrion in Michigan

This study examined pig carcasses buried at two different depths, 30 and 60 cm, to determine if insects were able to colonize buried carcasses, when they arrive at each depth, and what fauna were present over seven sampling dates to establish an insect succession database on buried carrion in East Lansing, MI. Thirty-eight pigs were buried, 18 at 30 cm and 20 at 60 cm. Four control carcasses were placed on the soil surface. Three replicates at each depth were exhumed after 3, 7, 14, 21, 30, and 60 d, respectively. One pig also was exhumed from 60 cm after 90 d and another after 120 d. Sarcophaga bullata (Parker) (Diptera: Sarcophagidae) and Hydrotaea sp. (Diptera: Muscidae) were found colonizing buried carrion 5 d after burial at 30 cm. Insect succession at 30 cm proceeded with flesh and muscid flies being the first to colonize, followed by blow flies. Insects were able to colonize carcasses at 60 cm and Hydrotaea sp. and Megaselia scalaris (Loew) (Diptera: Phoridae) were collected 7 d after burial. Insect succession at 60 cm did not proceed similarly, instead muscid and coffin flies were the only larvae collected. Overall these results reveal postburial interval estimates for forensic investigations in mid-Michigan during the summer, depending on climatic and soil conditions.

Comparative transcriptomics of early dipteran development

BackgroundModern sequencing technologies have massively increased the amount of data available for comparative genomics. Whole-transcriptome shotgun sequencing (RNA-seq) provides a powerful basis for comparative studies. In particular, this approach holds great promise for emerging model species in fields such as evolutionary developmental biology (evo-devo).ResultsWe have sequenced early embryonic transcriptomes of two non-drosophilid dipteran species: the moth midge Clogmia albipunctata, and the scuttle fly Megaselia abdita. Our analysis includes a third, published, transcriptome for the hoverfly Episyrphus balteatus. These emerging models for comparative developmental studies close an important phylogenetic gap between Drosophila melanogaster and other insect model systems. In this paper, we provide a comparative analysis of early embryonic transcriptomes across species, and use our data for a phylogenomic re-evaluation of dipteran phylogenetic relationships.ConclusionsWe show how comparative transcriptomics can be used to create useful resources for evo-devo, and to investigate phylogenetic relationships. Our results demonstrate that de novo assembly of short (Illumina) reads yields high-quality, high-coverage transcriptomic data sets. We use these data to investigate deep dipteran phylogenetic relationships. Our results, based on a concatenation of 160 orthologous genes, provide support for the traditional view of Clogmia being the sister group of Brachycera (Megaselia, Episyrphus, Drosophila), rather than that of Culicomorpha (which includes mosquitoes and blackflies).

Myiasis by <I>Megaselia scalaris</I> (Diptera: Phoridae) in a Python Affected by Pulmonitis

Myiases are caused by the presence of maggots in vertebrate tissues and organs. Myiases have been studied widely in humans, farm animals, and pets, whereas reports of myiasis in reptiles are scarce. We describe a case of myiasis caused by the Megaselia scalaris (Loew) in an Indian python (Python molurus bivittatus, Kuhl) (Ophida: Boidae). The python, 15 yr old, born and reared in a terrarium in the mainland of Venice (Italy), was affected by diffuse, purulent pneumonia caused by Burkholderia cepacia. The severe infestation of maggots found in the lungs during an autopsy indicated at a myiasis.

Interaction effects of temperature and food on the development of forensically important fly, Megaselia scalaris (Loew) (Diptera: Phoridae)

In forensic entomology, breeding of fly larvae in a controlled laboratory environment using animal tissue is a common technique to obtain insect developmental time for the estimation of postmortem interval. Previous studies on growth media are mostly on the effect of different diets on fly development. However, the interaction effects between temperature and food type used have not been explored. The objective of this study was to compare the use of cow's liver agar and raw liver on the development of a forensically important fly, Megaselia scalaris (Loew). This study also determined the interaction between different temperatures and different food types on the growth of this species. A total of 100 M. scalaris eggs were transferred into each of the two media mentioned above. Liver agar was prepared by adding dried ground liver into nutrient agar, whilst raw liver was naturally prepared from the same animal source. This experiment was conducted at 27, 30 and 33 °C in an incubator in a continuously dark condition. Length and weight of larvae, puparia and adult samples were determined. Total developmental times for larvae feeding on liver agar at each temperature were approximately 7-15 h slower than those feeding on raw liver. Survival rates were almost equal in both diets but were lower at 33 °C. Mean larva length in both diets did not differ significantly at all temperatures, but larvae feeding on liver agar had lower mean weight values than those in raw liver at 30 and 33 °C. The effect of temperature was significant in female puparia weight and male adult weight whereas the effect of diet types was significant in both male and female puparia size and weight. Interaction effects of temperature and food type on M. scalaris puparium size and adult weight were significant, indicating that puparium size and adult weight depended on both food type and temperature. This experiment highlighted the use of cow's liver agar as an alternative diet to breed M. scalaris in the laboratory and the importance of considering the interaction effect between temperatures and food types when deciding the most suitable medium in fly larva rearing.

BMP-dependent serosa and amnion specification in the scuttle fly Megaselia abdita

Bone morphogenetic protein (BMP) signaling is an essential factor in dorsoventral patterning of animal embryos but how BMP signaling evolved with fundamental changes in dorsoventral tissue differentiation is unclear. Flies experienced an evolutionary reduction of extra-embryonic tissue types from two (amniotic and serosal tissue) to one (amnionserosal tissue). BMP-dependent amnioserosa specification has been studied in Drosophila melanogaster. However, the mechanisms of serosal and amniotic tissue specification in less diverged flies remain unknown. To better understand potential evolutionary links between BMP signaling and extra-embryonic tissue specification, we examined the activity profile and function of BMP signaling in serosa and amnion patterning of the scuttle fly Megaselia abdita (Phoridae) and compared the BMP activity profiles between M. abdita and D. melanogaster. In blastoderm embryos of both species, BMP activity peaked at the dorsal midline. However, at the beginning of gastrulation, peak BMP activity in M. abdita shifted towards prospective amnion tissue. This transition correlated with the first signs of amnion differentiation laterally adjacent to the serosa anlage. Marker-assisted analysis of six BMP signaling components (dpp, gbb, scw, tkv, sax, sog) by RNA interference revealed that both serosa and amnion specification of M. abdita are dependent on BMP activity. Conversely, BMP gain-of-function experiments caused sharpened expression boundaries of extra-embryonic target genes indicative of positive feedback. We propose that changes in the BMP activity profile at the beginning of gastrulation might have contributed to the reduction of extra-embryonic tissue types during the radiation of cyclorrhaphan flies.

Five New Species of Scuttle Fly (Diptera: Phoridae) from Southern Africa

Diplonevra longifistula sp. n., D. meridafricana sp. n., D. stuckenbergi sp. n., Phalacrotophora petersoni sp. n. and Ph. stuckenbergi sp. are described. A revised key to Afrotropical Diplonevra species and a key to Afrotropical species of Phalacrotophora are provided.

Scuttle flies (Diptera: Phoridae) caught at dead mice in S. W. Finland

Scuttle flies trapped at baits of dead mice are reported from a region of S. W. Finland subjected to pollution from the smelt-ing of copper and nickel. Most belonged to the huge genus Megaselia, but 96% were females, the majority of which cannot be named until linked to their males. These are given code numbers and distinguished by means of a key.