Identification of Muscidae (Diptera) of medico-legal importance by means of wing measurements

Geometry of posterior larval spiracles to identify medically and forensically important calliphorids in Thailand

Fly identification is the primary step of analysis in forensic entomology. Although morphology and molecular techniques are considered satisfactory methods, some constraints may arise from a financial or even human point of view. Over the past decade, the geometric morphometric approach has been increasingly advocated for the classification and identification of arthropods. This study explored the method for species identification of 800 third-instar larvae of eight blow fly species of medical and forensic importance: Chrysomya chani Kurahashi, Chrysomya megacephala (Fabricius), Chrysomya (Ceylonomyia) nigripes Aubertin, Chrysomya pinguis (Walker), Chrysomya (Achoetandrus) rufifacies (Macquart), Hemipyrellia ligurriens (Wiedemann), Lucilia cuprina (Wiedemann), and Lucilia porphyrina (Walker). Based on the posterior spiracles geometry, the cross-validation revealed a relatively high percentage of correct classification in most species, ranking from 86% to 100%. The results of this study confirmed that the geometric morphometric (GM) analysis of posterior spiracles might be utilized as a larva identification tool. Therefore, this GM method represents one way of overcoming difficulties with the identification of blow fly larvae and can support further studies of these flies.

Wing measurements are a possible tool for the identification of European forensically important Sarcophagidae

The flesh flies are a group of insects well known for their forensic importance. Reliable identification of these flies relies on the use of either molecular markers or the morphology of the male genital apparatus. Identification of female flesh flies is more time consuming and less reliable than their male counterparts. This is particularly problematic for forensic entomology practitioners, because female flesh flies are more abundant than males in carrion arthropod assemblages. As such, it is critical that alternative methods for flesh fly identification are established that are equally effective for both sexes. One promising technique is the use of wing measurements, which have been shown to be reliable for the identification of some groups of necrophagous Diptera from several geographical regions. We applied this method to the European Sarcophagidae for the first time, using a dataset of 881 specimens representing 29 species and 5 genera. Species identifications were based on 15 landmarks located at wing vein junctions. We also combined our results with data from previous studies of Calliphoridae and Muscidae which utilised the same methodology, enabling the testing of family level identification using wing morphometrics. Species identifications using wing measurements had varied success. While some species were successfully identified without error, others, particularly from the genus Sarcophaga, were often misclassified. Notably, in several species wing measurements successfully identified both males and females. The results presented here suggest that wing measurements are a promising complementary method to other methods for the identification of necrophagous Sarcophagidae especially in material unsorted at the family level. It can also be used to double check identification performed by a taxonomist using traditional methods.

Size does matter: intraspecific geometric morphometric analysis of wings of the blowfly Chrysomya albiceps (Diptera: Calliphoridae)

Blowflies have forensic, sanitary and veterinary importance, as well as being pollinators, parasitoids and ecological bioindicators. There is still little work with real data and from experiments assessing the relationship between blowflies' morphologic features and environmental and demographic factors. The present work tests whether the variation, in the shape and size, of Chrysomya albiceps (Wiedemann, 1819) wings is influenced by the following factors: 1) time; 2) temperature; 3) sex and; 4) different types of carcasses (pig, dog/cat and whale). Male and female wings from four different sites collected in six different years were used to obtain wing size and shape of C. albiceps. Analyses between wing shape and the variables tested had low explanatory power, even though they had statistical support. However, it was possible to identify differences in wing shape between males and females, with good returns in sex identification. The comparison between wing size and the variables tested showed that wing size has a negative relationship with temperature, significant differences between sexes, slight variation over time and no influence by carcass types. Furthermore, wing size influenced wing shape. Understanding population-specific characteristics of C. albiceps provide important insights about how the species reacts under specific conditions.

Chrysomya pinguis (Walker) (Diptera: Calliphoridae), blow fly of forensic importance: A review of bionomics and forensic entomology appraisal

Role of blow flies as the entomological evidence used in forensic investigations has risen dramatically worldwide. As the diverse habitats of Thailand suitably endowed with biodiversity of insects, blow flies of forensic importance need investigation in their bionomics, which are further applied in forensic investigations. Chrysomya pinguis (Walker, 1858) (Diptera: Calliphoridae) make up one of the most common blow fly species found associated with the human corpses and/or death scenes in several countries of the Asia continent. Given the major species as forensically important, this review is performed by the need for gathering information of C. pinguis from literature search in the future application in the regions where this species exists. This review deals with morphology, current knowledge on bionomics and forensic entomology involvement. Important morphological characteristics of egg, larva, puparium and adult were highlighted with illustration and/or micrographs. Search pertaining to molecular analysis used for fly identification and developmental rate of larvae were included. Furthermore, we outline potential issues and challenges of C. pinguis research that necessitate forensic applications in the future.

Wing morphometrics as a tool for the identification of forensic important Lucilia spp. (Diptera: Calliphoridae)

Blow flies of the genera Lucilia Robineau-Desvoidy (Diptera: Calliphoridae) are considered forensically important species across several regions of the world. Due to the similarity of adults, especially females, the usual methods based on morphology or even molecular techniques can experience some limitations; therefore, alternative or supportive tools are required. Recently, the landmark-based geometric morphometric analysis has been applied to discriminate many insects on genus and species level. Herein, we focus on wing morphometric analysis as a tool in classifying five species of Lucilia; three species from Thailand - L. cuprina (Wiedemann, 1830), L. porphyrina (Walker, 1856) and L. sinensis Aubertin, 1933; and two species from Switzerland - L. caesar (Linnaeus, 1758) and L. illustris (Meigen, 1826). Canonical variate analysis of 233 right wings showed four overlapping clusters of L. cuprina, L. sinensis, L. caesar, and L. illustris with one distinct cluster of L. porphyrina. Eighty-eight to 100 percent of correct classification was achieved, with an UPGMA dendrogram analysis revealing clear-cut branch and sub-branch of five species determined. Results from this study suggested that wing morphometric analysis is a useful tool for the identification of adult Lucilia spp.

The Head of Fannia pusio (Fanniidae: Diptera) as A Novel Source of Morphometric Data for Assessing of Variation Along Geographic and Biological Lines

Fannia Robineau-Desvoidy, 1830 is the most diverse genus in the family Fanniidae (Diptera), with 288 species, many of which are include many of sanitary, economic and legal interest. The morphological homogeneity within the genus often makes species determination difficult. The best option for correct identification is to combine molecular and morphological analyses. The variation in the shape of a selection of body characters can be assessed by Geometric Morphometrics using the head as an innovative structure. Sex must be accounted for as a key covariate in this kind of study, since Fannia, as many other Diptera, has a sexually dimorphic head structure, with holoptic males and dicoptic females. Firstly, we analysed a set of Fannia sp. specimens sampled across the Iberian Peninsula (2012-2015), of which Fannia pusio (Wiedemann, 1830) was found to be the most abundant species. Our analyses provide significant morphological information. Fannia pusio exhibits clear intraspecific morphometric variation along an Iberian-wide East-West axis. A similar pattern emerged when comparing a laboratory-bred colony and wild samples.

Wing morphometrics of medically and forensically important muscid flies (Diptera: Muscidae)

Many muscid flies (Diptera: Muscidae) are well-known as medical, veterinary, and forensically significant insects, thus correct species identification is critically important before applying for fly control and determining a minimal postmortem interval (PMI_min) in forensic investigations. Limited in taxonomic keys and taxonomists, as well as scanty in advanced molecular laboratories lead to difficulty in identification of muscids. To date, a landmark-based geometric morphometric analysis of wings has proven to be a promising alternative technique for identifying many insect species. Herein, we assessed wing morphometric analysis for identification of six medically and forensically important muscids, namely Musca domestica Linnaeus, Musca pattoni Austen, Musca ventrosa Wiedemann, Hydrotaea chalcogaster (Wiedemann), Hydrotaea spinigera Stein, and Dichaetomyia quadrata (Wiedemann). A total of 302 right wing images were digitized based on 15 homologous landmarks and wing shape variation among genera and species was analyzed using canonical variate analysis, whereas sexual shape dimorphism of M. domestica, M. ventrosa, and D. quadrata was analyzed using discriminant function analysis. The cross-validation revealed a relatively high percentage of correct classification in most species, ranging from 86.4% to 100%, except for M. pattoni, being 67.5%. Misidentifications were mainly due to cross-pairings of the genus Musca; M. domestica VS M. pattoni VS M. ventrosa. The accuracy of classification using cross-validation test demonstrated that wing shape can be used to evaluate muscid flies at the genus- and species-level, and separate sexes of the three species analyzed, with a high reliability. This study sheds light on genus, species, and sex discrimination of six muscid species that have been approached using wing morphometric analysis.

Technical note: A technique to mount Sarcophagidae and Calliphoridae (Diptera) larvae for forensic identification using geometric morphometrics

Geometric morphometric analyses use landmark coordinates from images of specific areas on specimens. Therefore, to minimize differences arising from human preparation, preparation of the specimen is crucial. The application of geometric morphometrics has been used in entomology for identifying adult dipteran species, however, applying this technique to larval specimens requires the production of standard protocols which would allow specimens to be compared equally. This proposed protocol consists of a two-step process:

1. using 15% potassium hydroxide (KOH) to clear the specimen, followed by rinsing the specimen with 80% ethanol;

2. removal and spreading of the mouthhooks on a slide for imaging and analysis.

The goal of this work is to standardize specimen preparation, which would reduce human error and facilitate use of geometric morphometrics to identify dipteran larvae.

Role of Chrysomya albiceps (Diptera: Calliphoridae) and Musca domestica (Diptera: Muscidae) Maggot Crop Contents in Identifying Unknown Cadavers

Forensic entomology focuses on the analysis of insect larvae present at crime scenes to help identify unknown cadavers. Carrion-feeding maggots store food in a crop located at the anterior end of the gut. DNA recovered from the crop can be amplified, sequenced, and identified to determine the origin of the food. This information could help investigators to identify a missing victim if maggots are discovered at a crime scene in the absence of a corpse. Chrysomya albiceps (Wiedemann) and Musca domestica (Linnaeus) are primary forensic species. Little or no information on the identification of unknown cadavers using C. albiceps and M. domestica larvae is available, and we aimed to compare the effectiveness of using the crop contents of instars of C. albiceps and M. domestica larvae to identify corpses at different time intervals. Two hundred and forty larvae of both species were reared on rat and/or mouse liver, and DNA from crop contents was extracted after different time intervals from different instar larvae. DNA was amplified using specific primers that match the mitochondrial cytochrome oxidase subunit I (mt COI) gene of the food source. Results showed that food provided to larvae affected life span and the ability to be used to identify unknown cadavers. Chrysomya albiceps larvae proved more useful than M. domestica larvae. Moreover, crop contents of third instar larvae of both species fed for 24 h are more useful than contents from other time intervals in identifying unknown tissues. Results are promising and may help investigators to identify unknown/missing victims.

Wing morphometrics for identification of forensically important blowflies (Diptera: Calliphoridae) in Iberian Peninsula

Calliphoridae is a family of Diptera of great forensic interest because some of its species belong to the sarcosaprophagous diptera community, as their larvae are necrophagous or necrophilous. In the Iberian Peninsula there are six species that stand out, as they are the first insects to arrive at carrion: Calliphora vicina, Calliphora vomitoria, Lucilia sericata, Lucilia caesar, Chrysomya albiceps and Chrysomya megacephala. To differentiate among these blowflies, we compared the value of using traditional and geometric morphometrics by performing a morphometric analysis of the wings (shape and size). A total of 600 individuals were considered, segregated by species and sex equally. Seventeen landmarks per wing were recognized, and then centroid size and shape analyses were performed using geometric morphometrics, and size using traditional morphometrics, to identify species and sex. The results showed differences in shape among the species and it was found that landmarks 2 to 11 were the most variable, while the landmarks located at the base of the wings were relatively stable. However, according to both traditional and geometric morphometrics, no significant differences were found among species in wing size (Calliphora vicina, Chrysomya megacephala and Lucilia caesar were indistinguishable), but females were larger than males (except for the two Chrysomya species). Our results indicate that the use of geometric morphometrics to analyze wing configuration (shape) is an easy-to-use tool that helps to distinguish among common blowfly species of forensic importance.

Wing morphometrics for the identification of Nearctic and Palaearctic Piophilidae (Diptera) of forensic relevance

The Piophilidae (Diptera) are a family comprising about 80 species, several of them of high economic and forensic relevance. An unequivocal species identification is crucial for designing effective control measures or to provide reliable estimations of the minimum post mortem interval. However, the identification may sometimes not be possible, either because the diagnostic morphological characters are not easily observable or very fragile, or because of a poor DNA quality and/or unavailability of reference molecular signatures. In the recent years, the use of wing morphometric techniques has emerged as a powerful tool for the identification of different families of forensically important Diptera. The present study applies, for the first time, this technique to the identification of 11 Piophilidae species of forensic relevance in the Nearctic and Palaearctic regions, as well as to the discrimination of sexes, distinct geographical populations and, in the case of the dimorphic species Prochyliza nigrimana (Meigen), seasonal morphs. Wing shape variation was analysed using 14 landmarks located at wing vein junctions and a cross-variation analysis was used to test the reliability of identifications. The present results demonstrate that wing shape can be used to identify most species with relatively high success, whereas cross-validation analyses indicated that discrimination between sexes, populations or morphs was less effective, even if significant differences were observed in every comparison. We conclude that wing morphometrics can be a powerful identification tool that might be used in combination with other methods in order to achieve accurate and reliable species identifications-independently of the sex, geographic origin or colour variation of the samples-even with those piophilid species that have been object of frequent misidentifications.

Wing morphometric analysis of forensically important flesh flies (Diptera: Sarcophagidae) in Thailand

Flesh flies are insects of forensic importance as the larvae associated with human remains can be used to estimate a minimum post-mortem interval (PMI_min) in most cases. And, because life-history traits can vary across species, correct identification is a mandatory step before being used as evidence. Adult flesh flies are extremely similar in general appearance, which causes difficulty in species identification as it is largely based on the morphology of the male genitalia; this also makes it difficult to identify females. Currently, landmark-based geometric morphometric analysis of insect wings has proven to be a valuable tool for species identification. Herein, we applied wing morphometric analysis of 524 flesh fly specimens comprising 12 species from Thailand. The right wing of each specimen was removed, mounted on a microscope slide, photographed, and digitized using 18 landmarks. Wing shape variation among genera and species were analyzed using canonical variate analysis, while wing shape variation between sexes of each species was analyzed using discriminant function analysis. A cross-validation test was used to evaluate the reliability of classification. Results of this study demonstrate wing shape can be used to separate genera and species, and distinguish between sexes of the same species, with high reliability. Therefore, the landmark-based geometric morphometric analysis of wings is a useful additional method for species and sex discrimination of flesh flies.

Characterization and Identification of Puparia of Hydrotaea Robineau-Desvoidy, 1830 (Diptera: Muscidae) From Forensic and Archaeological Contexts

Flies and beetles are the main components of the entomofauna colonizing a body after death. Following the recognition of constant and predictable colonization patterns and the knowledge about the dependence of the insect development to temperature, a new discipline, forensic entomology, has provided information useful to reconstruct criminal events. Funerary archaeoentomology has also applied the same rationale in archaeological contexts. Puparia represent a large fraction of the insect remains that can be found associated with a cadaver, especially when the body is mummified or in the advanced stages of decomposition. Puparium identification is still a problematic topic due to the lack of identification keys and, in several cases, a lack of diagnostic feature descriptions. Here, we focus the attention on some Hydrotaea Robineau-Desvoidy (Diptera, Muscidae) puparia from forensic and archaeological contexts. Puparia of Hydrotaea capensis (Wiedemann), Hydrotaea ignava (Harris), Hydrotaea aenescens (Wiedemann), Hydrotaea similis Meade, Hydrotaea pilipes Stein, and Hydrotaea dentipes (Fabricius) are here detailed and illustrated. Posterior spiracles, anal plate, and intersegmental spines have been considered as good diagnostic characters for the identification of these puparia.

Predatory behavior of Synthesiomyia nudiseta larvae (Diptera: Muscidae) on several necrophagous blowfly species (Diptera: Calliphoridae)

Intraguild interactions play a prominent role in sarcosaprophagous communities, so intraspecific and interspecific competition phenomena between fly larvae take place. Synthesiomyia nudiseta is a species that has recently been recorded on human corpses in Europe, and it has been cited in forensic cases in Spain and Italy. The mature larvae are known to be facultative predators on necrophagous fly larvae, but their role as predators is unknown. The aim of this paper is to investigate the predatory behavior of S. nudiseta on the most abundant blowfly larvae in sarcosaprophagous communities in southwestern Europe (i.e., Chrysomya albiceps, Lucilia sericata, and Calliphora vicina). Intraspecific and interspecific competition experiments were carried out to study the effect of this species in the necrophagous diptera community. First-instar larvae were placed in plastic cups with the same amount of pig liver (15 g) at different densities (50, 100, 150, and 300 individuals/cup). Mortality in blowflies increased when S. nudiseta larvae were present: up to 98.40% in Ch. albiceps, 89.60% in L. sericata, and 84.93% in C. vicina. Pre-imaginal developmental time and adult wing size were analyzed and compared under each of the intraspecific and interspecific conditions; both variables were affected by competition in all cases. The implications of the presence of S. nudiseta for sarcosaprophagous community dynamics and its effect on the estimation of postmortem interval (PMI) are discussed.

Species identification of adult African blowflies (Diptera: Calliphoridae) of forensic importance

Necrophagous blowflies can provide an excellent source of evidence for forensic entomologists and are also relevant to problems in public health, medicine, and animal health. However, access to useful information about these blowflies is constrained by the need to correctly identify the flies, and the poor availability of reliable, accessible identification tools is a serious obstacle to the development of forensic entomology in the majority of African countries. In response to this need, a high-quality key to the adults of all species of forensically relevant blowflies of Africa has been prepared, drawing on high-quality entomological materials and modern focus-stacking photomicroscopy. This new key can be easily applied by investigators inexperienced in the taxonomy of blowflies and is made available through a highly accessible online platform. Problematic diagnostic characters used in previous keys are discussed.