Wing morphometry as a tool for correct identification of primary and secondary New World screwworm fly

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.

Leveraging machine learning tools and algorithms for analysis of fruit fly morphometrics

Analysis of landmark-based morphometric measurements taken on body parts of insects have been a useful taxonomic approach alongside DNA barcoding in insect identification. Statistical analysis of morphometrics have largely been dominated by traditional methods and approaches such as principal component analysis (PCA), canonical variate analysis (CVA) and discriminant analysis (DA). However, advancement in computing power creates a paradigm shift to apply modern tools such as machine learning. Herein, we assess the predictive performance of four machine learning classifiers; K-nearest neighbor (KNN), random forest (RF), support vector machine (the linear, polynomial and radial kernel SVMs) and artificial neural network (ANNs) on fruit fly morphometrics that were previously analysed using PCA and CVA. KNN and RF performed poorly with overall model accuracy lower than "no-information rate" (NIR) (p value > 0.1). The SVM models had a predictive accuracy of > 95%, significantly higher than NIR (p < 0.001), Kappa > 0.78 and area under curve (AUC) of the receiver operating characteristics was > 0.91; while ANN model had a predictive accuracy of 96%, significantly higher than NIR, Kappa of 0.83 and AUC was 0.98. Wing veins 2, 3, 8, 10, 14 and tibia length were of higher importance than other variables based on both SVM and ANN models. We conclude that SVM and ANN models could be used to discriminate fruit fly species based on wing vein and tibia length measurements or any other morphologically similar pest taxa. These algorithms could be used as candidates for developing an integrated and smart application software for insect discrimination and identification. Variable importance analysis results in this study would be useful for future studies for deciding what must be measured.

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.

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.

Random forests for predicting species identity of forensically important blow flies (Diptera: Calliphoridae) and flesh flies (Diptera: Sarcophagidae) using geometric morphometric data: Proof of concept

Wing shape variation has been shown to be useful for delineating forensically important fly species in two Diptera families: Calliphoridae and Sarcophagidae. Compared to DNA-based identification, the cost of geometric morphometric data acquisition and analysis is relatively much lower because the tools required are basic, and stable softwares are available. However, to date, an explicit demonstration of using wing geometric morphometric data for species identity prediction in these two families remains lacking. Here, geometric morphometric data from 19 homologous landmarks on the left wing of males from seven species of Calliphoridae (n = 55), and eight species of Sarcophagidae (n = 40) were obtained and processed using Generalized Procrustes Analysis. Allometric effect was removed by regressing centroid size (in log₁₀ ) against the Procrustes coordinates. Subsequently, principal component analysis of the allometry-adjusted Procrustes variables was done, with the first 15 principal components used to train a random forests model for species prediction. Using a real test sample consisting of 33 male fly specimens collected around a human corpse at a crime scene, the estimated percentage of concordance between species identities predicted using the random forests model and those inferred using DNA-based identification was about 80.6% (approximate 95% confidence interval = [68.9%, 92.2%]). In contrast, baseline concordance using naive majority class prediction was 36.4%. The results provide proof of concept that geometric morphometric data has good potential to complement morphological and DNA-based identification of blow flies and flesh flies in forensic work.

Molecular and morphometric divergence of four species of butterflies (Nymphalidae and Pieridae) from the Western Himalaya, India

Morphometric and molecular divergence among four butterfly species of the families Nymphalidae and Pieridae from the western Himalaya region were investigated using molecular tools, traditional morphometric measures and a truss network system. The considered species were Danaus chrysippus, Vanessa cardui, Pieris brassicae and Pieris canidia. Traditional taxonomy is sometimes unable to discriminate cryptic species or species that have close morphological features. Although taxonomists carefully examine external body features to differentiate the species; however, there is a risk for misidentification during a visual assessment of cryptic species. Therefore, we aimed to use the truss network system of 14 morphological landmarks interconnected to yield 90 variables about molecular taxonomy. Principal component analysis (PCA), discriminant function analysis (DFA) and cluster analysis (CA) were employed to determine morphometric variations. In the traditional analysis, 79, 68, 16 and 5 characters out of 90 were found significant (p < 0.05) for D. chrysippus, V. cardui, P. brassicae and P. canidia, respectively. One to seven principal components were extracted through PCA; they explained 87.5-100% of the total variance in samples. Notably, DFA correctly classified 100% of the original grouped cases and 100% of the cross-validated grouped cases. However, the variations were not the same for the two different methods (truss and traditional) employed for the analysis. We correctly identified all the species; the interspecies sequence divergence was between 0.1034 and 0.1398, and the intra-species sequence divergence range was 0.0001 to 0.0128 using the Cytochrome c oxidase subunit-I (COI) gene. The present study provides useful information about the application and complementary role of traditional with truss morphometric analysis for the precise identification and classification of the selected species.

A review on the occurrence of Cochliomyia hominivorax (Diptera: Calliphoridae) in Brazil

Cochliomyia hominivorax (Coquerel, 1858), the New World screwworm, causes primary myiasis in wild and domestic animals in tropical and subtropical regions of Brazil. Although this species is considered to occur throughout the country, organized information about its recorded distribution has not been available until now. This article aimed to provide a comprehensive review of the historical and current data published on both immature (myiasis) and adult stages of C. hominivorax in Brazil. A total of 174 articles were found; of these, 141 articles reported myiasis cases in cattle (146 records), humans (68 records), and other mammalian hosts (40 records), and captures of adult flies were reported in 33 articles. C. hominivorax is widespread in Brazil, having been recorded in 208 municipalities in all major biomes of the country.

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.

A molecular, morphological, and physiological comparison of English and German populations of Calliphora vicina (Diptera: Calliphoridae)

The bluebottle blow fly Calliphora vicina is a common species distributed throughout Europe that can play an important role as forensic evidence in crime investigations. Developmental rates of C. vicina from distinct populations from Germany and England were compared under different temperature regimes to explore the use of growth data from different geographical regions for local case work. Wing morphometrics and molecular analysis between these populations were also studied as indicators for biological differences. One colony each of German and English C. vicina were cultured at the Institute of Legal Medicine in Frankfurt, Germany. Three different temperature regimes were applied, two constant (16°C & 25°C) and one variable (17–26°C, room temperature = RT). At seven time points (600, 850, 1200, 1450, 1800, 2050, and 2400 accumulated degree hours), larval lengths were measured; additionally, the durations of the post feeding stage and intrapuparial metamorphosis were recorded. For the morphometric and molecular study, 184 females and 133 males from each C. vicina population (Germany n = 3, England n = 4) were sampled. Right wings were measured based on 19 landmarks and analyzed using canonical variates analysis and discriminant function analysis. DNA was isolated from three legs per specimen (n = 61) using 5% chelex. A 784 bp long fragment of the mitochondrial cytochrome b gene was sequenced; sequences were aligned and phylogenetically analyzed. Similar larval growth rates of C. vicina were found from different geographic populations at different temperatures during the major part of development. Nevertheless, because minor differences were found a wider range of temperatures and sampling more time points should be analyzed to obtain more information relevant for forensic case work. Wing shape variation showed a difference between the German and English populations (P<0.0001). However, separation between the seven German and English populations at the smaller geographic scale remained ambiguous. Molecular phylogenetic analysis by maximum likelihood method could not unambiguously separate the different geographic populations at a national (Germany vs England) or local level.

Forewing structure of the solitary bee Osmia bicornis developing on heavy metal pollution gradient

Wild bees in natural conditions can develop under various environmental stressors. Heavy metal pollution of the environment is one of the most widely studied stressors in insects, yet its effect is poorly described in bees. We have measured how pollution of the environment along a zinc, cadmium and lead contamination gradient in Poland affects bee development, using red mason bees (Osmia bicornis) as a model and their forewing asymmetry measures to assess possible developmental instabilities. We have also described wing asymmetry measures in the red mason bee-an important managed pollinator species-for the first time. The development of bee larvae in a contaminated environment did not affect forewing asymmetry measures, but it did lead to a negative correlation of wing size with contamination in females. Bees also showed a clear change in their asymmetry measures between various seasons, suggesting other, unknown environmental factors affecting wing asymmetry more than pollution. Sexes were found to have different forewing shape and size, larger females having larger forewings than the smaller males. The direction of size asymmetry was in favour of the left side in both sexes and also shape differences between the left and right wings showed similar tendencies in males and females. The levels of forewing shape and size asymmetry were smaller in females, making them the more symmetrical sex.

Wing morphometrics as a tool in species identification of forensically important blow flies of Thailand

Background

Correct species identification of blow flies is a crucial step for understanding their biology, which can be used not only for designing fly control programs, but also to determine the minimum time since death. Identification techniques are usually based on morphological and molecular characters. However, the use of classical morphology requires experienced entomologists for correct identification; while molecular techniques rely on a sound laboratory expertise and remain ambiguous for certain taxa. Landmark-based geometric morphometric analysis of insect wings has been extensively applied in species identification. However, few wing morphometric analyses of blow fly species have been published.

Methods

We applied a landmark-based geometric morphometric analysis of wings for species identification of 12 medically and forensically important blow fly species of Thailand. Nineteen landmarks of each right wing of 372 specimens were digitised. Variation in wing size and wing shape was analysed and evaluated for allometric effects. The latter confirmed the influence of size on the shape differences between species and sexes. Wing shape variation among genera and species were analysed using canonical variates analysis followed by a cross-validation test.

Results

Wing size was not suitable for species discrimination, whereas wing shape can be a useful tool to separate taxa on both, genus and species level depending on the analysed taxa. It appeared to be highly reliable, especially for classifying Chrysomya species, but less robust for a species discrimination in the genera Lucilia and Hemipyrellia. Allometry did not affect species separation but had an impact on sexual shape dimorphism.

Conclusions

A landmark-based geometric morphometric analysis of wings is a useful additional method for species discrimination. It is a simple, reliable and inexpensive method, but it can be time-consuming locating the landmarks for a large scale study and requires non-damaged wings for analysis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2163-z) contains supplementary material, which is available to authorized users.

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

Cadavers attract numerous species and genera of Muscidae, both regular elements of carrion insect assemblages, and accidental visitors. Identification of adult Muscidae may be considered difficult, particularly by non-experts. Since species identification is a vital first step in the analysis of entomological material in any forensic entomology orientated experiment and real cases, various alternative methods of species identification have been proposed. We investigated possibility of semiautomated identification by means of wing measurements as an alternative for classic morphology and DNA-based approaches. We examined genus-level identification success for 790 specimens representing 13 genera of the most common European cadavers visiting Muscidae. We found 99.8% of examined specimens correctly identified to the genus-level. Without error, the following were identified: Azelia, Eudasyphora, Graphomya, Hydrotaea, Musca, Muscina, Mydaea, Neomyia, Polietes, Stomoxys and Thricops. Genus-level misidentifications were found only in Helina and Phaonia. Discrimination of examined material on the species level within Hydrotaea (318 specimens representing eight species) and Muscina (163 specimens representing four species) showed lower, yet still high average identification success, 97.2 and 98.8%, respectively. Our results revealed relatively high success in both genus and species identification of Muscidae of medico-legal importance. Semiautomated identification by means of wing measurements can be used by non-experts and does not require sophisticated equipment. This method will facilitate the identification of forensically relevant muscids in comparison to more difficult and more time-consuming identification approaches based on taxonomic keys or DNA-based methods. However, for unambiguous identification of some taxa, we recommend complementary use of identification keys.

Establishment of a satellite rearing facility to support the release of sterile Aedes albopictus males. I. Optimization of mass rearing parameters

The vector species Aedes albopictus (Skuse, 1894) was recorded in Turkey for the first time, near the Greek border, in 2011 and a high risk of expansion towards Aegean and Mediterranean coasts of Turkey was estimated. A preliminary study was planned to evaluate the possibility of creating a satellite mass rearing facility for this species and manage a larval rearing procedure by using the new mass-rearing technology proposed by the International Atomic Energy Agency (IAEA). For this purpose, the effects of different larval densities (1, 2, 3 and 4 larvae per ml) on the preimaginal development were evaluated by observing pupal, adult and male productivity using life cycle trials. Geometric morphometric analyses were also performed to define all phenotypic differences that occurred on the wing size and shape morphology of adult stage at the four different rearing conditions tested. A high pupation productivity was obtained with a larval density of 2 larvae/ml while adult emergence ratio was not affected by the densities tested. No significant difference was observed in shape of the wings among different densities in males and females. Nevertheless, a significant difference in female's centroid sizes was observed between the treatment groups 1-2 and 3-4 larvae/ml and in males centroid size reared at 1 larvae/ml versus the other densities.

Use of wing morphometrics to identify populations of the Old World screwworm fly, Chrysomya bezziana (Diptera: Calliphoridae): a preliminary study of the utility of museum specimens

The Old World screwworm (OWS) fly, Chrysomya bezziana (Diptera: Calliphoridae), is a major economic and welfare problem for humans and animals in the Old World tropics. Using a bootstrapped log likelihood ratio test of the output of Procrustes principal components and canonical variates analyses for a small sample of museum specimens from which 19 2D wing landmarks had been collected: (1) a consistent and statistically significant difference exists between landmark configurations derived from wings of pinned specimens and those removed from the body and mounted on slides; (2) a highly statistically significant sexual dimorphism in wing morphometry was identified; and (3) a highly statistically significant difference in wing morphometry between populations of the OWS fly from Africa (Tanzania, South Africa Sudan, Zaire, Zimbabwe,) and Asia (Sumba, Indonesia) exists. These results show that wing orientation and gender must be considered when conducting morphometric investigations of OWS fly wings. The latter result is also consistent with results from previous molecular and morphological studies, which indicate there are two distinct genetic lineages within this species. Wing morphometry holds great promise as a practical tool to aid in identification of the geographical origin of introductions of this important pest species, by providing diagnostic markers to distinguish geographical populations and complement molecular diagnostics.

An Overview of the Components of AW-IPM Campaigns against the New World Screwworm

The New World Screwworm, Cochliomyia hominivorax (Coquerel), is one of the most damaging parasites of livestock, causing millions of dollars in annual losses to producers. The fly is an obligate parasite of warm-blooded animals, including humans. After a successful 50-year eradication campaign, C. hominivorax has been eradicated from the USA, Mexico and Central America by an area-wide integrated pest management approach. Recently, Caribbean and South American countries have expressed an interest in this approach. Aiming to support forthcoming projects in these countries, this review describes the main technical components of past and ongoing AW-IPM campaigns against C. hominivorax.

Temporal patterns of genetic and phenotypic variation in the epidemiologically important drone fly, Eristalis tenax

Eristalis tenax L. (Diptera: Syrphidae) is commonly known as the drone fly (adult) or rat-tailed maggot (immature). Both adults and immature stages are identified as potential mechanical vectors of mycobacterial pathogens, and early-stage maggots cause accidental myiasis. We compared four samples from Mount Fruška Gora, Serbia, with the aim of obtaining insights into the temporal variations and sexual dimorphism in the species. This integrative approach was based on allozyme loci, morphometric wing parameters (shape and size) and abdominal colour patterns. Consistent sexual dimorphism was observed, indicating that male specimens had lighter abdomens and smaller and narrower wings than females. The distribution of genetic diversity at polymorphic loci indicated genetic divergence among collection dates. Landmark-based geometric morphometrics revealed, contrary to the lack of divergence in wing size, significant wing shape variation throughout the year. In addition, temporal changes in the frequencies of the abdominal patterns observed are likely to relate to the biology of the species and ecological factors in the locality. Hence, the present study expands our knowledge of the genetic diversity and phenotypic plasticity of E. tenax. The quantification of such variability represents a step towards the evaluation of the adaptive potential of this species of medical and epidemiological importance.

The exchangeability of shape

BACKGROUND

Landmark based geometric morphometrics (GM) allows the quantitative comparison of organismal shapes. When applied to systematics, it is able to score shape changes which often are undetectable by traditional morphological studies and even by classical morphometric approaches. It has thus become a fast and low cost candidate to identify cryptic species. Due to inherent mathematical properties, shape variables derived from one set of coordinates cannot be compared with shape variables derived from another set. Raw coordinates which produce these shape variables could be used for data exchange, however they contain measurement error. The latter may represent a significant obstacle when the objective is to distinguish very similar species.

RESULTS

We show here that a single user derived dataset produces much less classification error than a multiple one. The question then becomes how to circumvent the lack of exchangeability of shape variables while preserving a single user dataset. A solution to this question could lead to the creation of a relatively fast and inexpensive systematic tool adapted for the recognition of cryptic species.

CONCLUSIONS

To preserve both exchangeability of shape and a single user derived dataset, our suggestion is to create a free access bank of reference images from which one can produce raw coordinates and use them for comparison with external specimens. Thus, we propose an alternative geometric descriptive system that separates 2-D data gathering and analyzes.