Diversity response of necrophagous dipteran communities and their functional groups to an anthropization gradient

The anthropization process exerts a profound effect on ecosystems, causing alterations in biodiversity, habitat structure, and species composition, ultimately disrupting the delicate balance of natural environments. The aim of the present study was to explore the ecological dynamics of necrophagous Sarcophagidae and Calliphoridae flies along an anthropization gradient. This research investigated alpha and beta diversity patterns to unravel the impact of human-induced environmental changes on these insect communities and also assesses the dynamics of functional groups in relation to their impact on medical and forensic fields. Five distinct habitats, ranging from urban to forested areas, were surveyed in two Departments in the Province of Chaco, Argentina. Necrophagous flies were collected using van Someren-Rydon canopy traps across three seasons. Two main functional groups were analyzed: oviparous flies (Calliphoridae) and larviparous flies (Sarcophagidae). Results indicated a significant negative correlation between Sarcophagidae species richness and anthropization, whereas Calliphoridae showed increased abundance in highly anthropized sites. The combined assemblage of Calliphoridae+Sarcophagidae exhibited significant relationships across all community parameters evaluated. Beta diversity analysis revealed turnover as the main process shaping dipteran communities along the anthropization gradient, with spatial species replacement dominating. This underscores the importance of interspecific spatial segregation in dipteran community composition. In conclusion, this study enhances our understanding of the ecological adaptations of necrophagous dipterans to anthropogenic disturbances. The observed shifts in diversity and abundance have implications for forensic investigations and public health, emphasizing the need for nuanced monitoring and conservation strategies. This research contributes valuable insights into the intricate ecological interactions of these insect communities within changing ecosystems.

Distinguishing Four Calliphoridae Species (Diptera) from Jamaica Using the Cephalopharyngeal Skeleton: Application to Forensic Investigations

Flies of the family Calliphoridae, commonly called blow flies, are important in the decomposition process. Knowledge on their succession pattern on corpses, species identification and the duration of their life cycle stages can be useful in forensic investigations especially when estimating the post-mortem interval. We performed linear-based morphometrics on the cephalopharyngeal skeleton of four blow fly species found in Jamaica to distinguish species and determine larval development stage. We collected eggs from pigs' heads used as bait in the field and conducted rearing exercises in the laboratory. We used the internal skeletonized structure, the cephalopharyngeal skeleton, to develop a practical and efficient method for species identification. For the first instar, we found species can be differentiated using all the measurements analysed in the study. We found that the mouth hook length may be useful in distinguishing larvae in the second instar. For the larvae in the third instar, the whole length of the skeleton, from mouth hook to length of the dorsal cornue, may be useful for separating species. We provide information on the cephalopharyngeal skeleton of Lucilia lucigerens (James), a blow fly species endemic to Jamaica, for the first time. Our work provides relevant information that could be utilized for species identification and life stage determination if fly evidence is to be incorporated in forensic investigations in Jamaica.

Differential responses of adult Calliphora vicina to dry bloodstains on porous versus non-porous surface materials

Necrophagous flies are presumed to feed on wet and dried blood at crime scenes, but no empirical information exists detailing fly interactions with dried bloodstains. In the present study, the foraging behavior of adult Calliphora vicina was characterized during interactions with dried bloodstains formed on a variety of porous, and non-porous materials that are commonly encountered in a household. Continuous digital recording and image analysis were used to monitor fly interactions with dried bloodstains and to determine mechanisms of stain modification. Flies displayed differential responses to bloodstains based on the porosity and topography of the surface material. For instance, blood that was not tightly adhered to the materials was flaked or dislodged by fly activity and was not consumed by the flies. On other non-porous surfaces, most stains were consumed following moistening by regurgitation. Feeding activity on such bloodstains frequently yielded partial, perimeter and skeletal stains. In contrast, adult flies rarely mechanically altered dried blood on porous fabrics and there was no evidence of modification due to feeding. Feeding avoidance behavior was observed due to tactile inhibition with blood dried on rough, uneven surfaces like cotton and denim.

It is all about the insects: a retrospective on 20 years of forensic entomology highlights the importance of insects in legal investigations

This study highlights the importance of insect evidence by evaluating 949 insect-associated cases, including 139 entomological reports, from 2001 to 2019 at the Institute of Legal Medicine Frankfurt/Germany. With a high number of cases in the summer months and a low number in the colder season, 78.5% of the bodies were found indoors, regardless of year or month. In more than 80% of the cases, where PMI information was available (n = 704), the presumed PMI ranged from 1 to 21 days, a period during which entomological evidence can provide a day-specific estimate of PMI_min. In cases where insects have been identified to species level (n = 279), most bodies were infested by one or two species with a maximum of 10 different species. Overall, a total of 55 insect species were found. Information on biology, activity and distribution of the most abundant taxa is given and applied for 5 case histories estimating different PMI_mins of up to over 6 months. Despite proved importance and scientific development of forensic entomology, insects are still rarely considered as a tool in forensic case work. The main reasons are a lack of awareness and (too) late involvement of a forensic entomologist. Our work shows that forensic entomology is an independent discipline that requires specialist expertise.

Age-dependent gene expression of Calliphora vicina pupae (Diptera: Calliphoridae) at constant and fluctuating temperatures

Estimating the age of the developmental stages of the blow fly Calliphora vicina (Diptera: Calliphoridae) is of forensic relevance for the determination of the minimum post-mortem interval (PMI_min). Fly eggs and larvae can be aged using anatomical and morphological characters and their modification during development. However, such methods can only hardly be applied for aging fly pupae. Previous study described age estimation of C. vicina pupae using gene expression, but just when reared at constant temperatures, but fluctuating temperatures represent a more realistic scenario at a crime scene. Therefore, age-dependent gene expression of C. vicina pupae were compared at 3 fluctuating and 3 constant temperatures, the latter representing the mean values of the fluctuating profiles. The chosen marker genes showed uniform expression patterns during metamorphosis of C. vicina pupae bred at different temperature conditions (constant or fluctuating) but the same mean temperature (e.g. constant 10 °C vs. fluctuating 5–15 °C). We present an R-based statistical tool, which enables estimation of the age of the examined pupa based on the analysed gene expression data.

The use of wing fray and sex ratios to determine the origin of flies at an indoor crime scene

When adult flies are collected at indoor crime scenes, the question of their origin arises, i.e., whether they originated from the outdoors, coming in to oviposit on the body, or if they developed through the larval and pupal stages from eggs laid on the body. This is particularly important if no empty puparia were collected, potentially because they were overlooked, with a consequent impact on the accuracy of the minimum post-mortem interval estimation. This study used two methods to determine if flies sampled in various experimental conditions and at an actual crime scene were wild flies attracted to the body or had developed on the body, i.e., through the assessment of: (1) wing fray and; (2) sex ratio. A template was created to measure the amount of wing fray damage quantitatively in a simple, rapid and efficient manner. The experiments demonstrated that by combining the two methods it is possible to establish the origin of a population of adult flies at a crime scene.

A survey of bacteria associated with various life stages of primary colonizers: Lucilia sericata and Phormia regina

Blow flies are common primary colonizers of carrion, play an important role in the transfer of microbes between environments, and serve as a vector for many human pathogens. While some investigation has begun regarding the bacteria associated with different life stages of blow flies, a well replicated study is currently not available for the majority of blow flies. This study investigated bacteria associated with successive life stages of blow fly species Lucilia sericata and Phormia regina. A total of 38 samples were collected from four true replicates of L. sericata and P. regina. Variable region four (V4) of 16S ribosomal DNA (16S rDNA) was amplified and sequenced on MiSeq FGx sequencing platform using universal 16S rDNA primers and dual-index sequencing strategy. Bacterial communities associated with different life stages of L. sericata and P. regina didn't differ significantly from each other. In both blow fly species, Bacilli (e.g., Lactococcus) and Gammaproteobacteria (e.g., Providencia) constituted >95% of all bacterial classes across all life stages. At the genus level, Vagococcus and Leuconostoc were present at relatively high abundances in L. sericata whereas Yersinia and Proteus were present at comparatively high abundances in P. regina. Overall, information on bacterial structures associated with various life stages of blow flies can help scientists in better understanding or management of vector-borne pathogen dispersal and in increasing the accuracy of microbial evidence based postmortem interval (PMI) prediction models.

Precocious egg development in wild Calliphora vicina (Diptera: Calliphoridae) - An issue of relevance in forensic entomology?

The list of factors influencing the development of forensically important insects and the related effects on minimum post mortem (PMI_min) estimations is long and well established by various authors in forensic entomology over the last decades. Despite the fact that several authors mention precocious egg development, i.e. first instar larva in the genital tract of some species of Calliphoridae, as a potential error source for PMI_min estimations just two studies were performed to examine the occurrence of precocious eggs both in laboratory and field populations of blow flies. In the present study the occurrence of gravid females with precocious eggs in a wild population of Calliphora vicina in Frankfurt am Main was surveyed over 152 days and their seasonal distribution was analyzed as well as the influence of abiotic variables on their abundance. During the sampling occasions, 5.216 females were sampled of which 44 % were gravid. 54 % of all gravid females had a precocious egg/first instar larva in their genital tract. This number varied depending on the season and showed the highest amount in spring with almost 64 % of all gravid females. Hence, precocious eggs in wild populations of blow flies can occur much more frequently than mentioned in forensic literature. Consequences for the evaluation of entomological evidence in forensic casework should not be overrated since focusing alone on the largest larva in a sample is not recommended as the sole reference in an entomological PMI_min estimation. The entomological report has to justify its findings, discuss different options and finally state what is considered to be the most likely scenario based on the complete evidence (e.g. including all species and relevant age cohorts as well as succession data) and the case specific history.

First molecular phylogeny of Paralucilia Brauer & Bergenstamm, 1891 (Insecta, Diptera, Calliphoridae): A preliminary approach

Paralucilia Brauer & Bergenstamm, 1891 (Diptera, Oestroidea, Calliphoridae) is a small genus of blowflies restricted to the Neotropical region, which is commonly reported on decaying corpses and vertebrate carcasses. The number of species currently assigned to this genus and their denominations are contentious, with either three or five species recognized by different authors. This taxonomic instability results in a lack of consensus in species determination, making it impossible to compare results from different studies as well as to elaborate confident taxonomic keys. In order to solve some of the most commonly reported taxonomic conflicts within this genus, to the best of our knowledge, this study presents the first phylogenetic hypothesis for the relationships among Paralucilia species, based on molecular analysis of the COI, ITS2, 28S, and 16S genes. Maximum parsimony, maximum likelihood, and Bayesian inference analyses were used for phylogenetic reconstruction and divergence time estimation analyses. Intra- and interspecific genetic distances were calculated among species using the COI dataset. The results showed that at least three of the five currently accepted species are well defined: P. fulvinota, P. pseudolyrcea, and P. paraensis, however, a significant level of intraspecific variation was observed in P. fulvinota. These findings will assist future revisions of the description, classification, and distribution of species of Paralucilia, as well as in the elaboration of taxonomic keys. Additionally, we show that it is possible to clarify the evolutionary history of this Neotropical genus using supplementary evidence such as morphology and molecular data.

50 years later, insect evidence overturns Canada's most notorious case - Regina v. Steven Truscott

On 11 June 1959, the body of 12-year old Lynne Harper was discovered in a woodlot northeast of Clinton, Ontario. Although insect evidence was photographed and collected at the scene and autopsy, this evidence was not used in the 1959 trial. Instead, time of death was pinpointed to a 45-min window of 1900-1945 h on 9 June 1959 based on stomach content analysis. Based on circumstantial evidence and this time frame that he was the last suspect to see her alive, 14-year old Steven Truscott was convicted of her murder. He was scheduled to be hanged, but a temporary reprieve postponed his execution. In 1960, his death sentence was commuted to life imprisonment. Truscott was the youngest person to be sentenced to death in Canada, and his case provided the major impetus toward abolition of the death penalty in Canada. Truscott always maintained his innocence. In 2001, the Association in Defence of the Wrongly Convicted filed an appeal to have the case reopened. In 2006, the authors of this paper were contacted by Attorneys James Lockyer and Phil Campbell of the LCP Law Firm in Toronto to investigate this case. Fresh evidence was presented at the Ontario Court of Appeal in 2006-2007 including testimony of 3 forensic entomologists. This resulted in controversy regarding identification of the insects and assumptions of insect behaviour that affected the postmortem interval estimate. Lack of scientific evidence for the controversial theories proposed by one testifying entomologist resulted in disregarding his testimony. Instead, testimony by VanLaerhoven and Merritt was accepted. Based on their analysis and a re-creation experiment of the insect evidence, initial fly colonization occurred during daylight hours of 10 June 1959. The collected larvae were not likely to have been deposited on the body before dark (2140 h) on 9 June 1959 as this would have resulted in significantly larger and more advanced larval instar than were collected at the scene or autopsy. This analysis, together with a pathology reanalysis of stomach content analysis, demonstrated that the original estimate of time of death was unreliable. Truscott was with numerous witnesses prior to 1900 h and after 2000 h on 9 June 1959, thus the estimate of time of death was the most critical evidence in the original 1959 trial and the 2006-2007 appeal. On 28 August 2007, his conviction was overturned, declared a wrongful conviction and miscarriage of justice. Steven Truscott was acquitted of the murder charges.

Environmental dissemination of mcr-1 positive Enterobacteriaceae by Chrysomya spp. (common blowfly): An increasing public health risk

Until recently, the role of insects, and particularly flies, in disseminating antimicrobial resistance (AMR) has been poorly studied. In this study, we screened blowflies (Chrysomya spp.) from different areas near the city of Phitsanulok, Northern Thailand, for the presence of AMR genes and in particular, mcr-1, using whole genome sequencing (WGS). In total, 48 mcr-1-positive isolates were recovered, consisting of 17 mcr-1-positive Klebsiella pneumoniae (MCRPKP) and 31 mcr-1-positive Escherichia coli (MCRPEC) strains. The 17 MCRPKP were shown to be clonal (ST43) with few single poly nucleomorphs (SNPs) by WGS analysis. In in-vitro models, the MCRPKP were shown to be highly virulent. In contrast, 31 recovered MCRPEC isolates are varied, belonging to 12 different sequence types shared with those causing human infections. The majority of mcr-1 gene are located on IncX4 plasmids (29/48, 60.42%), sharing an identical plasmid backbone. These findings highlight the contribution of flies to the AMR contagion picture in low- and middle-income countries and the challenges of tackling global AMR.

Analysis of the 13C isotope ratios of amino acids in the larvae, pupae and adult stages of Calliphora vicina blow flies and their carrion food sources

Adult blow flies are one of the first necrophagous insects to colonize fresh carcasses. The eggs they lay hatch into larvae, which then feed on the decomposing body. Like all organisms, blow flies "are what they eat," meaning that the isotopic composition of their body tissues reflects their diet. This manuscript combines ecology with a forensic application by using isotope ratio mass spectrometry (IRMS) to understand the relationship between the δ¹³C of amino acids in different carrion sources and the blow fly that feed on them. We also measure the amino acid-level fractionation that occurs at each major life stage of the blow flies. Adult blow flies from a commercial strain of Calliphora vicina (Robineau-Desvoidy) (Diptera: Calliphoridae) oviposited on raw pork muscle, beef muscle, or chicken liver. Larvae, pupae, and adult blow flies from each carrion were selected for amino acid compound-specific isotope analysis. Canonical discriminant analysis showed that flies were correctly classified to specific carrion types in 100% (original rules) and 96.8% (leave-one-out cross-validation [LOOCV]) of cases. Regarding life stages, we obtained 100% and 71% of correct classification in original rules and LOOCV, respectively. The isotope ratios of most of the essential amino acids did not significantly change between life stages (at 95% CI). However, some non-essential amino acids (Ala, Ser, and Glu) and some conditionally essential amino acids (Gly and Pro) were isotopically depleted in the adult stage. Except for the essential amino acids, the amino acids in larvae and pupae were enriched in ¹³C, and adult blow flies were depleted in ¹³C relative to the carrion on which they fed. These results make it possible to exclude potential sources of carrion as larval food. Amino acid-specific IRMS could help inform entomologists whether a fly has just arrived from another location to feed on a corpse or has emerged from a pupa whose feedstock was the corpse. Such insight could enhance the significance of blow flies for post-mortem interval determinations. The analytical ability to link organisms from one trophic level to another through the use of compound-specific isotope analysis of amino acids could have wide-reaching consequences in a variety of disciplines. Graphical abstract ᅟ.

Ultrastructure of male genitalia of blow flies (Diptera: Calliphoridae) of forensic importance

Male genitalia of blow flies (Diptera: Calliphoridae) are distinctive in their morphological features and are often used for species identification. The aim of this work was to investigate the male genitalia of blow flies of medical and forensic importance from Thailand at the ultrastructural level, using scanning electron microscopy (SEM). Flies in two subfamilies were examined: Chrysomyinae [Chrysomya bezziana Villeneuve, Chrysomya chani Kurahashi, Chrysomya nigripes Aubertin, Chrysomya pinguis (Walker), Chrysomya rufifacies (Macquart), Chrysomya thanomthini Kurahashi & Tumrasvin, and Chrysomya villeneuvi Patton] and Luciliinae [Hemipyrellia ligurriens (Wiedemann), Hypopygiopsis infumata (Bigot), Hypopygiopsis tumrasvini Kurahashi, Lucilia cuprina (Wiedemann), Lucilia papuensis Macquart, Lucilia porphyrina (Walker), and Lucilia sinensis Aubertin]. Particular attention was paid to the main distinguishing features such as the shapes of the cercus and the surstylus, and the complex structure of the distiphallus. The differentiation of the male genitalia of these species at the SEM level is discussed and compared to the conditions in closely related species such as Chrysomya megacephala (Fabricius). A key for the identification of 14 blow fly species based on male genitalia is provided.

Use of necrophagous insects as evidence of cadaver relocation: myth or reality?

The use of insects as indicators of post-mortem displacement is discussed in many texts, courses and TV shows, and several studies addressing this issue have been published. Although the concept is widely cited, it is poorly understood, and only a few forensic cases have successfully applied such a method. The use of necrophagous insects as evidence of cadaver relocation actually involves a wide range of biological aspects. Distribution, microhabitat, phenology, behavioral ecology, and molecular analysis are among the research areas associated with this topic. This article provides the first review of the current knowledge and addresses the potential and limitations of different methods to evaluate their applicability. This work reveals numerous weaknesses and erroneous beliefs as well as many possibilities and research opportunities.

Effects of different storage and measuring methods on larval length values for the blow flies (Diptera: Calliphoridae) Lucilia sericata and Calliphora vicina

In forensic entomology, the methods of sampling, killing, and storing entomological samples can affect larval age estimation, and, hence, the estimation of the minimum post-mortem interval. In the existing manuals, there is a certain amount of heterogeneity regarding methods and the recommendations for best practice in forensic entomology are insufficiently validated. This study evaluated three different length-measurement methods for larval stages and examined the influence of different killing and storing methods on the larval length of two forensically important blow flies, Lucilia sericata and Calliphora vicina. The three different measuring methods were a) a ruler with a 0.1mm scale, b) a geometrical micrometer, and c) a computer-aided stereomicroscope. They were used to measure the length of L₁-L₃C. vicina larvae and detect no significant differences. This supports the view that a simple tool like a geometrical micrometer can produce reliable results in forensic entomology. Newly hatched larvae of L. sericata and C. vicina were killed with hot water (HW) and divided into two equal subsamples. Lengths of all larvae were measured immediately after killing, then every 24h until day 4, and once more after 7days of storage in ≥70%-ethanol. L. sericata larvae only showed significant changes in length in the HW group stored at room temperature. After 4 and 7days of storage, these 24-h- and 72-h-old larvae showed a significant decrease in length compared with those in a fridge at 6°C. This decrease can, however, be considered a negligible natural variation without forensically relevant consequences for larval age estimation of L. sericata samples. For C. vicina, an increase in length was observed over time. This was significant only for younger larvae (24-48h old) stored in 70%-ethanol. This variance in length can lead to a wrong estimation of age; however, only for larvae stored in 70%-ethanol, not for those stored in 96%-ethanol.

NOVELTY STATEMENT

We examined the influence of different killing and storing methods on two forensically important blow flies, Lucilia sericata and Calliphora vicina. For the latter species we additionally were evaluating three different length measurement methods. The results of both experiments suggest that it is possible to kill and store fly larvae directly in (not hot) ≥70%-ethanol. This simplifies the sampling and storing of fly evidence at the crime scene. We also compared the influence of three different measuring methods for estimating the length of L1-L3 C. vicina larvae by using a) a ruler with a 0,1mm scaling, b) a geometrical micrometer and c) a computer-aided stereomicroscope. No significant differences were detected, supporting the view, that a simple tool like a geometrical micrometer can produce reliable results. This study helps to simplify the sampling and evaluation of entomological evidence and to backup or questioning existing guidelines and best practice recommendations.

Assemblage of Necrophagous Diptera in Atlantic Insular Environments and Response to Different Levels of Human Presence

Islands act as natural laboratories for ecological studies to explain bioinvasion processes and, in this scenario, necrophagous Diptera have never been used as model organisms. This study aimed to (i) describe assemblages of necrophagous Diptera (Calliphoridae and Sarcophagidae) in two insular environments of different origins and distances from mainland, (ii) investigate the effect of anthropogenic impact on the assemblage of carrion flies, (iii) to quantify the establishment of invasive species in the two islands, and (iv) to infer about the conservation status of the islands based on the ecological parameters. Sampling was performed in 2011-2012, in the dry and rainy season. Insects were collected by using traps with chicken liver or sardine baits. In each island, environments exposed to different degrees of human impact were sampled. Ecological analyses were carried out to characterize the assemblages of Calliphoridae and Sarcophagidae, with emphasis on the relation between native and invasive species. In total, 99,862 adults of 21 species of blow flies and flesh flies were collected. Overall abundance in the oceanic island was higher than in the continental island, although the richness of species was higher in the latter. The type of bait did not influence diversity of species sampled in either island. No difference was observed in total richness of both families according to the gradient of anthropogenic impact, in both islands. The invasive species Chrysomya megacephala (Fabricius) was classified as dominant in all environments, irrespective of the anthropogenic impact, which raises concern about the conservation status of each island.

Death eaters respond to the dark mark of decomposition day and night: observations of initial insect activity on piglet carcasses

Some insect taxa can be of critical importance for criminal investigations because they can be used to assist with a time since death determination. Blow flies (Diptera: Calliphoridae) often are the initial colonizers of a carcass, usually arriving within minutes to hours after carcass exposure during the day. Other insects, such as coleopterans and hymenopterans, can arrive to a carcass during early colonization and affect blow fly development. However, the extent of these interactions remains unclear. This study analyzed the initial 6 h after a piglet carcass was placed out in two locations (rural and urban) in diurnal and nocturnal conditions with continuous video recording and hourly observations. Four piglets were placed out every 2 weeks over the summer of 2014. Initial blow fly arrivals to the carcasses were only recorded during diurnal conditions, and a checklist of orders associated with each environment (time and location) was created. During diurnal conditions, initial blow fly arrival times in rural environments were significantly faster than those in urban, arriving as quickly as 23 s after exposure. These observations also included a novel interaction with Vespidae, which to the best of our knowledge has not been seen in the literature before. This experiment provides baseline data on early insect colonization in two environments in New Jersey, and lends insight into insect interactions that could affect initial colonization.