Ontogenetic study of three Calliphoridae of forensic importance through cuticular hydrocarbon analysis

Discrimination of Diptera order insects based on their saturated cuticular hydrocarbon content using a new microextraction procedure and chromatographic analysis

The nature and proportions of hydrocarbons in the cuticle of insects are characteristic of the species and age. Chemical analysis of cuticular hydrocarbons allows species discrimination, which is of great interest in the forensic field, where insects play a crucial role in estimating the minimum post-mortem interval. The objective of this work was the differentiation of Diptera order insects through their saturated cuticular hydrocarbon compositions (SCHCs). For this, specimens fixed in 70 : 30 ethanol : water, as recommended by the European Association for Forensic Entomology, were submitted to solid-liquid extraction followed by dispersive liquid-liquid microextraction, providing preconcentration factors up to 76 for the SCHCs. The final organic extract was analysed by gas chromatography coupled with flame ionization detection (GC-FID), and GC coupled with mass spectrometry was applied to confirm the identity of the SCHCs. The analysed samples contained linear alkanes with the number of carbon atoms in the C9-C15 and C18-C36 ranges with concentrations between 0.1 and 125 ng g-1. Chrysomya albiceps (in its larval stage) showed the highest number of analytes detected, with 21 compounds, while Lucilia sericata and Calliphora vicina the lowest, with only 3 alkanes. Non-supervised principal component analysis and supervised orthogonal partial least squares discriminant analysis were performed and an optimal model to differentiate specimens according to their species was obtained. In addition, statistically significant differences were observed in the concentrations of certain SCHCs within the same species depending on the stage of development or the growth pattern of the insect.

Effects of antibiotics ceftriaxone and levofloxacin on the growth of Protophormia terraenovae (Diptera: Calliphoridae)

Protophormia terraenovae is a colonizer of decomposing bodies and is known to cause pre-mortem myiasis as the female flies lay eggs in uncleaned wounds. In this study the effects of different concentrations of antibiotics levofloxacin and ceftriaxone on maggot development, weight, length, and mortality were examined. The maggot length and weight were significantly increased by therapeutical doses of levofloxacin and ceftriaxone. The maggot development time was significantly decreased in every levofloxacin treatment compared to the control. The time to start pupation was significantly increased in the control compared to the antibiotic treatments. Levofloxacin significantly increased the survivability of the maggots. Every levofloxacin treatment significantly improved the rearing conditions for the maggots. Reaching the third instar was delayed by 24 h in the control compared to the Levo 3.57 treatment. The Pupation in the control was delayed by an average of 48 h compared to the Levo 3.57 treatment. The significantly reduced development time of the maggots in the antibiotic treatments might lead to an overestimation of the post-mortem interval and therefore an incorrect time of death determination. The improved rearing conditions may be an indication of the potential of a combined application of antibiotics and maggot therapy.

Development of Forensically Important Sarcophaga peregrina (Diptera: Sarcophagidae) and Intra-Puparial Age Estimation Utilizing Multiple Methods at Constant and Fluctuating Temperatures

Sarcophaga peregrina (Robineau-Desvoidy, 1830) has the potential to estimate the minimum postmortem interval (PMI_min). Development data and intra-puparial age estimation are significant for PMI_min estimation. Previous research has focused on constant temperatures, although fluctuating temperatures are a more real scenario at a crime scene. The current study examined the growth patterns of S. peregrina under constant (25.75 °C) and fluctuating temperatures (18-36 °C; 22-30 °C). Furthermore, differentially expressed genes, attenuated total reflectance Fourier-transform infrared spectroscopy, and cuticular hydrocarbons of S. peregrina during the intra-puparial period were used to estimate age. The results indicated that S. peregrina at fluctuating temperatures took longer to develop and had a lower pupariation rate, eclosion rate, and pupal weight than the group at constant temperatures did. Moreover, we found that six DEG expression profiles and ATR-FTIR technology, CHCs detection methods, and chemometrics can potentially estimate the intra-puparial age of S. peregrina at both constant and fluctuating temperatures. The findings of the study support the use of S. peregrina for PMI_min estimation and encourage the use of entomological evidence in forensic practice.

Geographical Variation of Cuticular Hydrocarbon Profiles of Adult Flies and Empty Puparia Amongst Three Populations of Calliphora vicina (Diptera: Calliphoridae)

Blowflies (Diptera: Calliphoridae) are of great importance in forensic entomology and in determining the minimum post-mortem interval, as they may be the first group of insects to colonize decomposing remains. Reliable species identification is an essential prerequisite. Classically, morphological characters or DNA sequences are used for this purpose. However, depending on the species and the condition of the specimen, this can be difficult, e.g., in the case of empty fly puparia. Recent studies have shown that cuticular hydrocarbon (CHC) profiles are species-specific in necrophagous taxa and represent another promising tool for identification. However, the population-specific variability of these substances as a function of e.g., local climatic parameters has not yet been sufficiently investigated. The aim of this study was to determine the geographical variation of CHC profiles of the blowfly Calliphora vicina (Robineau-Desvoidy, 1830) depending on different countries of origin. Flies were reared in the United Kingdom, Germany, and Turkey in common garden experiments under ambient conditions. CHC profiles of the resulting adult flies and their empty puparia were analyzed using gas chromatography-mass spectrometry. Data were visualized by principal component analysis and clustered by population. The populations of the United Kingdom and Germany, both having similar climates and being geographically close to each other, showed greater similarities in CHC profiles. However, the CHC profile of the Turkish population, whose climate is significantly different from the other two populations, was very different. Our study confirms the high potential of CHC analysis in forensic entomology but highlights the need to investigate geographical variability in chemical profiles.

Predicting the Weathering Time by the Empty Puparium of Sarcophaga peregrina (Diptera: Sarcophagidae) with the ANN Models

Empty puparium are frequently collected at crime scenes and may provide valuable evidence in cases with a long postmortem interval (PMI). Here, we collected the puparium of Sarcophaga peregrina (Diptera: Sarcophagidae) (Robineau-Desvoidy, 1830) for 120 days at three temperatures (10 °C, 25 °C, and 40 °C) with the aim to estimate the weathering time of empty puparium. The CHC profiles were analyzed by gas chromatography-mass spectrometry (GC-MS). The partial least squares (PLS), support vector regression (SVR), and artificial neural network (ANN) models were used to estimate the weathering time. This identified 49 CHCs with a carbon chain length between 10 and 33 in empty puparium. The three models demonstrate that the variation tendency of hydrocarbon could be used to estimate the weathering time, while the ANN models show the best predictive ability among these three models. This work indicated that puparial hydrocarbon weathering has certain regularity with weathering time and can gain insight into estimating PMI in forensic investigations.

Near infrared spectroscopy (NIRS) coupled with chemometric methods to identify and estimate taxonomic relationships of flies with forensic potential (Diptera: Calliphoridae and Sarcophagidae)

Infrared spectroscopy has been gaining prominence in entomology, such as for solving taxonomic problems, sexing adult specimens, determining the age of immature specimens, detecting drugs of abuse in fly larvae, and can be an important technique in Forensic Entomology. In order to help identify the species of Calliphoridae and Sarcophagidae families, the present study aimed to evaluate the use of near infrared spectroscopy (NIRS) coupled with chemometric methods for separating fly specimens into taxonomic categories and understanding the taxonomic relationship between them. Spectra collected from nine species of flies were subjected to unsupervised principal component analysis (PCA) and hierarchical cluster analysis (HCA), in which we sought to visualize the relationship between the samples (segregation of genera and families) with subsequent identification. In PCA, the best model was achieved using five principal components (PCs), which explained 99.16% of total variance of the original data set. The first principal component (PC1) and the fourth principal component (PC4) provided the best segregation, the latter being more important in the segregation of the species Chrysomya albiceps, Lucilia eximia, and Ravinia belforti from the others. In the HCA dendrogram, there was a clear separation between the specimens by family (Calliphoridae and Sarcophagidae) and genera (Chrysomya, Lucilia, Oxysarcodexia, Peckia and Ravinia). This study shows that NIRS is efficient to identify flies' taxonomic properties, such as family and genera, providing quick evidence for the tested species identity.

Worker bees (Apis mellifera) deprived of pollen in the first week of adulthood exhibit signs of premature aging

Pollinator populations, including bees, are in rapid decline in many parts of the world, raising concerns over the future of ecosystems and food production. Among the factors involved in these declines, poor nutrition deserves attention. The diet consumed by adult worker honeybees (Apis mellifera) is crucial for their behavioral maturation, i.e., the progressive division of labor they perform, such as nurse bees initially and later in life as foragers. Poor pollen nutrition is known to reduce the workers' lifespan, but the underlying physiological and genetic mechanisms are not fully understood. Here we investigate how the lack of pollen in the diet of workers during their first week of adult life can affect age-related phenotypes. During the first seven days of adult life, newly emerged workers were fed either a pollen-deprived (PD) diet mimicking that of an older bee, or a control pollen-rich (PR) diet, as typically consumed by young bees. The PD-fed bees showed alterations in their fat body transcriptome, such as a switch from a protein-lipid based metabolism to a carbohydrate-based metabolism, and a reduced expression of genes involved with immune response. The absence of pollen in the diet also led to an accumulation of oxidative stress markers in fat body tissue and alterations in the cuticular hydrocarbon profiles, which became similar to those of chronologically older bees. Together, our data indicate that the absence of pollen during first week of adulthood triggers the premature onset of an aging-related worker phenotype.

Cuticular hydrocarbons for the identification and geographic assignment of empty puparia of forensically important flies

Research in social insects has shown that hydrocarbons on their cuticle are species-specific. This has also been proven for Diptera and is a promising tool for identifying important fly taxa in Forensic Entomology. Sometimes the empty puparia, in which the metamorphosis to the adult fly has taken place, can be the most useful entomological evidence at the crime scene. However, so far, they are used with little profit in criminal investigations due to the difficulties of reliably discriminate among different species. We analysed the CHC chemical profiles of empty puparia from seven forensically important blow flies Calliphora vicina, Chrysomya albiceps, Lucilia caesar, Lucilia sericata, Lucilia silvarum, Protophormia terraenovae, Phormia regina and the flesh fly Sarcophaga caerulescens. The aim was to use their profiles for identification but also investigate geographical differences by comparing profiles of the same species (here: C. vicina and L. sericata) from different regions. The cuticular hydrocarbons were extracted with hexane and analysed using gas chromatography-mass spectrometry. Our results reveal distinguishing differences within the cuticular hydrocarbon profiles allowing for identification of all analysed species. There were also differences shown in the profiles of C. vicina from Germany, Spain, Norway and England, indicating that geographical locations can be determined from this chemical analysis. Differences in L. sericata, sampled from England and two locations in Germany, were less pronounced, but there was even some indication that it may be possible to distinguish populations within Germany that are about 70 km apart from one another.

A Study of Cuticular Hydrocarbons of All Life Stages in Sarcophaga peregrina (Diptera: Sarcophagidae)

Sarcophaga peregrina (Robineau-Desvoidy, 1830), a synanthropic flesh fly species found in different parts of the world, is of medical and forensic importance. Traditional methods of inferring developmental age rely on the life stage of insects and morphological changes. However, once the larvae reach the pupal and adult stage, morphological changes would become barely visible, so that the classic method would be invalid. Here, we studied the cuticular hydrocarbon profile of S. peregrina of the whole life cycle from larval stage to adult stage by GC-MS. Sixty-three compounds with carbon chain length ranging from 8 to 36 were detected, which could be categorized into four classes: n-alkanes, branched alkanes, alkenes, and unknowns. As developmental increased, branched alkanes dominant, and the content of high-molecular-weight hydrocarbons is variable, especially for 2-methyl C19, DiMethyl C21, docosane (C22), and tricosane (C23). This study shows that the composition of CHC could be used to determine the developmental age of S. peregrina and aid in postmortem interval estimations in forensic science.

Body Size and Cuticular Hydrocarbons as Larval Age Indicators in the Forensic Blow Fly, Chrysomya albiceps (Diptera: Calliphoridae)

Chrysomya albiceps (Wiedemann 1819) is one of the most important insects in forensic entomology. Its larval developmental and survival rates are influenced by nutritional resources, temperature, humidity, and geographical regions. The present study investigated the possibility of relying on body size and cuticular hydrocarbon composition as indicators for age estimation of the different larval instars of C. albiceps. Larvae were maintained in standardized laboratory conditions at different experimental temperatures. All larval instars (first, second, and third) were randomly collected for measuring their body sizes and for estimating their cuticular hydrocarbons at different rearing temperatures (30, 35, 40, and 45°C) using gas chromatography-mass spectrometry (GC-MS). Results indicated that the duration of larval stage was temperature dependent as it gradually decreased on increasing the rearing temperature (30, 35, and 40°C) except 45°C at which larval development was ceased. In contrary, larval body size, in terms of length, width, and weight, was temperature dependent as it gradually increased with larval development on increasing rearing temperature except at 45°C at which larval development was ceased. The GC-MS showed a significant difference in the extracted components of cuticular hydrocarbons between different larval instars reared in the same temperature and between the same larval instar that reared at different temperatures. Furthermore, the highest and lowest amounts of cuticular hydrocarbons were detected at 35 and 40°C, respectively. Overall, larval body size and cuticular hydrocarbon components were temperature dependent within the range 30-40°C, which may suggest them as possible reliable age indicators for estimating the postmortem interval in the field of medicolegal entomology.

Cuticular hydrocarbons for identifying Sarcophagidae (Diptera)

The composition and quantity of insect cuticular hydrocarbons (CHCs) can be species-specific as well as sexually dimorphic within species. CHC analysis has been previously used for identification and ageing purposes for several insect orders including true flies (Diptera). Here, we analysed the CHC chemical profiles of adult males and females of eleven species of flesh flies belonging to the genus Sarcophaga Meigen (Sarcophagidae), namely Sarcophaga africa (Wiedemann), S. agnata Rondani, S. argyrostoma Robineau-Desvoidy, S. carnaria (Linnaeus), S. crassipalpis Macquart, S. melanura Meigen, S. pumila Meigen, S. teretirostris Pandellé, S. subvicina Rohdendorf, S. vagans Meigen and S. variegata (Scopoli). Cuticular hydrocarbons extracted from pinned specimens from the collections of the Natural History Museum, London using a customised extraction technique were analysed using Gas Chromatography-Mass Spectrometry. Time of preservation prior to extraction ranged between a few weeks to over one hundred years. CHC profiles (1) allowed reliable identification of a large majority of specimens, (2) differed between males and females of the same species, (3) reliably associated males and females of the same species, provided sufficient replicates (up to 10) of each sex were analysed, and (4) identified specimens preserved for up to over one hundred years prior to extraction.

Time Flies-Age Grading of Adult Flies for the Estimation of the Post-Mortem Interval

The estimation of the minimum time since death is one of the main applications of forensic entomology. This can be done by calculating the age of the immature stage of necrophagous flies developing on the corpse, which is confined to approximately 2–4 weeks, depending on temperature and species of the first colonizing wave of flies. Adding the age of the adult flies developed on the dead body could extend this time frame up to several weeks when the body is in a building or closed premise. However, the techniques for accurately estimating the age of adult flies are still in their beginning stages or not sufficiently validated. Here we review the current state of the art of analysing the aging of flies by evaluating the ovarian development, the amount of pteridine in the eyes, the degree of wing damage, the modification of their cuticular hydrocarbon patterns, and the increasing number of growth layers in the cuticula. New approaches, including the use of age specific molecular profiles based on the levels of gene and protein expression and the application of near infrared spectroscopy, are introduced, and the forensic relevance of these methods is discussed.

Volatile compounds reveal age: a study of volatile organic compounds released by Chrysomya rufifacies immatures

Age determination of insects collected from vertebrate remains is an essential step in estimating time since colonization as related to the post-mortem interval. Long-established methods for making such estimates rely on determining age related to stage of development at the time of collection in relation to conditions experienced. However, such estimates are based on the completion of a stage of development. Methods allowing for more precise estimates of age (i.e., within a stage of development) are sorely needed. This study examined the potential of volatile organic compounds emitted by blow fly, Ch. rufifacies (Macquart), immatures to determine stage of development, which could potentially be used to estimate the age. Volatile organic compounds (VOCs) from the larval and pupal stages of Ch. rufifacies were collected by headspace solid-phase micro-extraction followed by gas chromatography-mass spectrometry (GC-MS). Analyses indicated 37 compounds shift quantitatively, as well as qualitatively, as the larvae and pupae age. Furthermore, compounds, such as 2-ethyl-1-hexanol, phenol, butanoic acid, hexadecanoic acid, octadecanoic acid, 2-methyl propanamide, and 2-methyl butanoic acid, serve as indicator compounds of specific stages within Ch. rufifacies development. This information could be important to determine if these compounds can be used in the field to predict the presence of certain developmental stages, in order to determine the potential of using volatile markers to estimate time of colonization.

Eye-background contrast as a quantitative marker for pupal age in a forensically important carrion beetle Necrodes littoralis L. (Silphidae)

Insect pupae sampled at a death scene may be used to estimate the post-mortem interval. The pupal age is however difficult to estimate, as there are no good quantitative markers for the age of a pupa. We present a novel method for pupal age estimation based on the quantification of contrast in intensity between the eyes of a pupa and the middle grey photography card as a standard background. The intensity is measured on a standardized scale from 0 (perfect black) to 255 (perfect white) using computer graphical software and pictures of the eye and the background taken with a stereomicroscope. Eye-background contrast is calculated by subtracting the average intensity of the eye from the average intensity of the background. The method was developed and validated using pupae of Necrodes littoralis (Linnaeus, 1758) (Coleoptera: Silphidae), one of the most abundant beetle species on human cadavers in Central Europe. To develop the model, pupae were reared in 17, 20 and 23 °C, with a total of 120 specimens. The method was validated by three raters, using in total 182 pupae reared in 15, 17, 20, 23 and 25 °C. We found a gradual increase in eye-background contrast with pupal age. Changes followed generalized logistic function, with almost perfect fit of the model. Using our method pupal age was estimated with the average error of 8.1 accumulated degree-days (ADD). The largest error was 27.8 ADD and 95% of age estimates had errors smaller than 20 ADD. While using the method, different raters attained similar accuracy. In conclusion, we have demonstrated that eye-background contrast is a good quantitative marker for the age of N. littoralis pupae. Contrast measurements gave accurate estimates for pupal age. Our method is thus proven to be a candidate for a reliable approach to age insect pupae in forensic entomology.

The evolution of sexually dimorphic cuticular hydrocarbons in blowflies (Diptera: Calliphoridae)

Cuticular hydrocarbons (CHCs) are organic compounds found on the cuticles of all insects which can act as close-contact pheromones, while also providing a hydrophobic barrier to water loss. Given their widespread importance in sexual behaviour and survival, CHCs have likely contributed heavily to the adaptation and speciation of insects. Despite this, the patterns and mechanisms of their diversification have been studied in very few taxa. Here, we perform the first study of CHC diversification in blowflies, focussing on wild populations of the ecologically diverse genus Chrysomya. We convert CHC profiles into qualitative and quantitative traits and assess their inter- and intra-specific variation across 10 species. We also construct a global phylogeny of Chrysomya, onto which CHCs were mapped to explore the patterns of their diversification. For the first time, we demonstrate that blowflies express an exceptional diversity of CHCs, which have diversified in a nonphylogenetic and punctuated manner, are species-specific and sexually dimorphic. It is likely that both ecological and sexual selection have shaped these patterns of CHC diversification, and our study now provides a comprehensive framework for testing such hypotheses.

New method for estimating the post-mortem interval using the chemical composition of different generations of empty puparia: Indoor cases

Most flies of forensic importance are in two superfamilies, the Muscoidea and the Oestroidea, with similar life stages including the puparium. Upon completion of metamorphosis the adult fly emerges from the puparium, leaving behind an exuvia that is of potential significance in forensic investigation. The empty puparium is a durable piece of entomological evidence lasting several years. Through the study of chemical compounds, specifically the hydrocarbons of these puparia, it is possible to identify the species, in addition to how long they have been exposed to weathering and for this reason, these parameters can assist forensic entomologists in estimating long-term postmortem interval (minPMI). In corpses that take a relatively longer time to decompose, insects may use the same corpses for several oviposition cycles. Therefore, the aim of this study was to develop a new method to determine the PMI based on chemical compounds of the puparia from different oviposition cycles of the fly Chrysomya megacephala. The chemical composition of 50 puparia from different cycles of oviposition were evaluated by Gas Chromatography–Mass Spectrometry (GC-MS). In total, 60 compounds were identified ranging from C₁₈ to C₃₄, 38 of those were common to all generations. Our results demonstrate that chemical profiles can be used to differentiate puparia collected from successive cycles, and therefore valuable in the estimation of minPMI.

Phenotypic Plasticity of Cuticular Hydrocarbon Profiles in Insects

The insect integument is covered by cuticular hydrocarbons (CHCs) which provide protection against environmental stresses, but are also used for communication. Here we review current knowledge on environmental and insect-internal factors which shape phenotypic plasticity of solitary living insects, especially herbivorous ones. We address the dynamics of changes which may occur within minutes, but may also last weeks, depending on the species and conditions. Two different modes of changes are suggested, i.e. stepwise and gradual. A switch between two distinct environments (e.g. host plant switch by phytophagous insects) results in stepwise formation of two distinct adaptive phenotypes, while a gradual environmental change (e.g. temperature gradients) induces a gradual change of numerous adaptive CHC phenotypes. We further discuss the ecological and evolutionary consequences of phenotypic plasticity of insect CHC profiles by addressing the question at which conditions is CHC phenotypic plasticity beneficial. The high plasticity of CHC profiles might be a trade-off for insects using CHCs for communication. We discuss how insects cope with the challenge to produce and "understand" a highly plastic, environmentally dependent CHC pattern that conveys reliable and comprehensible information. Finally, we outline how phenotypic plasticity of CHC profiles may promote speciation in insects that rely on CHCs for mate recognition.

Communication in necrophagous Diptera larvae: interspecific effect of cues left behind by maggots and implications in their aggregation

Necrophagous Calliphoridae breed in vertebrate carrion. Their larvae aggregate and form large masses of individuals. These aggregated larvae can reach adulthood faster than scattered larvae, increasing their chances of survival. Furthermore, the gathering of larvae of different species suggests possible interspecific aggregation vectors. In this context, the effect of larval ground-left cues on larvae of Calliphora vomitoria and Lucilia sericata was studied. We used video tracking to follow larvae placed in binary choice tests. We observed (1) a preference of both species for a side marked by conspecific or heterospecific larvae compared to an unmarked side, (2) a preference of L. sericata larvae for a conspecific-marked side compared to a heterospecific-marked side but only at high concentration of cues and (3) a preference of both species for the side marked by the greater number of larvae. These results demonstrate that larvae leave a mark locally which is retentive, has an interspecific range, has an effect proportional to its intensity and whose strength varies depending on the emitting species. According to the self-organization theory, this mark could enhance larval gathering and promote interspecific aggregations. While not yet demonstrated, an interspecific Allee effect could explain the interspecific association of necrophagous calliphorid larvae.

Adult fly age estimations using cuticular hydrocarbons and Artificial Neural Networks in forensically important Calliphoridae species

Blowflies (Diptera: Calliphoridae) are forensically important as they are known to be one of the first to colonise human remains. The larval stage is typically used to assist a forensic entomologists with adult flies rarely used as they are difficult to age because they remain morphologically similar once they have gone through the initial transformation upon hatching. However, being able to age them is of interest and importance within the field. This study examined the cuticular hydrocarbons (CHC) of Diptera: Calliphoridae species Lucilia sericata, Calliphora vicina and Calliphora vomitoria. The CHCs were extracted from the cuticles of adult flies and analysed using Gas Chromatography-Mass Spectrometry (GC-MS). The chemical profiles were examined for the two Calliphora species at intervals of day 1, 5, 10, 20 and 30 and up to day 10 for L. sericata. The results show significant chemical changes occurring between the immature and mature adult flies over the extraction period examined in this study. With the aid of a Principal Component Analysis (PCA) and Artificial Neural Networks (ANN), samples were seen to cluster, allowing for the age to be established within the aforementioned time frames. The use of ANNs allowed for the automatic classification of novel samples with very good performance. This was a proof of concept study, which developed a method allowing to age post-emergence adults by using their chemical profiles.

The potential use of cuticular hydrocarbons and multivariate analysis to age empty puparial cases of Calliphora vicina and Lucilia sericata

Cuticular hydrocarbons (CHC) have been successfully used in the field of forensic entomology for identifying and ageing forensically important blowfly species, primarily in the larval stages. However in older scenes where all other entomological evidence is no longer present, Calliphoridae puparial cases can often be all that remains and therefore being able to establish the age could give an indication of the PMI. This paper examined the CHCs present in the lipid wax layer of insects, to determine the age of the cases over a period of nine months. The two forensically important species examined were Calliphora vicina and Lucilia sericata. The hydrocarbons were chemically extracted and analysed using Gas Chromatography – Mass Spectrometry. Statistical analysis was then applied in the form of non-metric multidimensional scaling analysis (NMDS), permutational multivariate analysis of variance (PERMANOVA) and random forest models. This study was successful in determining age differences within the empty cases, which to date, has not been establish by any other technique.

Potential Use of Cuticular Hydrocarbons in Estimating the Age of Blowfly Pupae Chrysomya megacephala (Diptera: Calliphoridae)

Gas chromatography coupled with mass spectrometry (GC–MS) was used to determine the weathering time in cuticular hydrocarbon of pupae Chrysomya megacephala in sheltered condition. The results have shown that cuticular hydrocarbons (CHC) of the pupae were a mixture of n-alkanes, methyl-branched alkanes, and dimethyl-branched alkanes, with carbon chain length ranging from C19 to C39.The study presents the significant correlation between the changes pattern in relative abundance of several CHC and development phase in pupae. Further analysis with multiple linear regression indicated that several CHC compounds showed strong correlation to blowfly pupae age, which were then utilized to create a prediction equation for the age estimation. Finally, the application of the age-dependent model had revealed that estimated age correlated significantly with chronological age of samples C. megacephala., y = 0.97x + 0.092, R2 = 0.9698. The study concluded that, CHC have a potential to estimate age of immature C. megacephala, and possibly in other flies species, and might further be used to determine the PMI.

Chemotaxonomic Profile and Intraspecific Variation in the Blow Fly of Forensic Interest Chrysomya megacephala (Diptera: Calliphoridae)

Necrophagous insects such as blow flies (Diptera: Calliphoridae) are considered crucial in forensic entomology. Identification at species level and determination of larval stage are the basis for estimation of postmortem interval (PMI). Insect evidence can also be used in the determination of crime scenes, since body displacement is common. The aim of this study was to determine the chemotaxonomic profile and intraspecific variability of the forensically important blow fly Chrysomya megacephala (F. 1794). Adults were collected in the municipalities of Dourados-MS (Brazil) and Rio Claro-SP (Brazil), and then transferred to the laboratory for oviposition and development of the immature stages. Chemical analysis of cuticular compounds was performed by gas chromatography. Cuticular chemical profiles varied significantly between the two populations, as well as between developmental stages, supporting the use of these compounds as a complementary tool to help identify the species and its stages, along with geographical variability. This could greatly accelerate forensic investigations, eliminating the need to allow the fly larvae to develop until adult stage in order to confirm the species identity and sample origin.

The potential and prospects of proximal remote sensing of arthropod pests

Bench-top or proximal remote sensing applications are widely used as part of quality control and machine vision systems in commercial operations. In addition, these technologies are becoming increasingly important in insect systematics and studies of insect physiology and pest management. This paper provides a review and discussion of how proximal remote sensing may contribute valuable quantitative information regarding identification of species, assessment of insect responses to insecticides, insect host responses to parasitoids and performance of biological control agents. The future role of proximal remote sensing is discussed as an exciting path for novel paths of multidisciplinary research among entomologists and scientists from a wide range of other disciplines, including image processing engineers, medical engineers, research pharmacists and computer scientists. © 2015 Society of Chemical Industry.

Effect of age on cuticular hydrocarbon profiles in adult Chrysomya putoria (Diptera: Calliphoridae)

A species-specific complex mixture of highly stable cuticular hydrocarbons (CHCs) covers the external surface of all insects. Components can be readily analyzed by gas chromatography coupled to mass spectrometry (GC-MS) to obtain a cuticular hydrocarbon profile, which may be used as an additional tool for the taxonomic differentiation of insect species and also for the determination of the age and sex of adult and immature forms. We used GC-MS to identify and quantify the CHCs of female and male Chrysomya putoria (Wiedemann, 1818) (Diptera: Calliphoridae) from one to five days old. CHCs ranged from C21 to C35 for females and from C21 to C37 in males. Major compounds were the same for both sexes and were 2-MeC28, C29:1, n-C29, 15-,13-MeC29, 2-MeC30, C31:1, n-C31 and 15-,13-MeC31. The relative abundance of each component, however, varied with age. Cluster Analysis using Bray-Curtis measure for abundance showed that cuticular hydrocarbon profiles are a strong and useful tool for the determination of age in adult C. putoria.

Remote Sensing and Reflectance Profiling in Entomology

Remote sensing describes the characterization of the status of objects and/or the classification of their identity based on a combination of spectral features extracted from reflectance or transmission profiles of radiometric energy. Remote sensing can be benchtop based, and therefore acquired at a high spatial resolution, or airborne at lower spatial resolution to cover large areas. Despite important challenges, airborne remote sensing technologies will undoubtedly be of major importance in optimized management of agricultural systems in the twenty-first century. Benchtop remote sensing applications are becoming important in insect systematics and in phenomics studies of insect behavior and physiology. This review highlights how remote sensing influences entomological research by enabling scientists to nondestructively monitor how individual insects respond to treatments and ambient conditions. Furthermore, novel remote sensing technologies are creating intriguing interdisciplinary bridges between entomology and disciplines such as informatics and electrical engineering.

Detection of temporal changes in insect body reflectance in response to killing agents

Computer vision and reflectance-based analyses are becoming increasingly important methods to quantify and characterize phenotypic responses by whole organisms to environmental factors. Here, we present the first study of how a non-destructive and completely non-invasive method, body reflectance profiling, can be used to detect and time stress responses in adult beetles. Based on high-resolution hyperspectral imaging, we acquired time series of average reflectance profiles (70 spectral bands from 434-876 nm) from adults in two beetle species, maize weevils (Sitophilus zeamais) and larger black flour beetles (Cynaus angustus). For each species, we acquired reflectance data from untreated controls and from individuals exposed continuously to killing agents (an insecticidal plant extract applied to maize kernels or entomopathogenic nematodes applied to soil applied at levels leading to ≈100% mortality). In maize weevils (exposed to hexanic plant extract), there was no significant effect of the on reflectance profiles acquired from adult beetles after 0 and 12 hours of exposure, but a significant treatment response in spectral bands from 434 to 550 nm was detected after 36 to 144 hours of exposure. In larger black flour beetles, there was no significant effect of exposure to entomopathogenic nematodes after 0 to 26 hours of exposure, but a significant response in spectral bands from 434-480 nm was detected after 45 and 69 hours of exposure. Spectral bands were used to develop reflectance-based classification models for each species, and independent validation of classification algorithms showed sensitivity (ability to positively detect terminal stress in beetles) and specificity (ability to positively detect healthy beetles) of about 90%. Significant changes in body reflectance occurred at exposure times, which coincided with published exposure times and known physiological responses to each killing agent. The results from this study underscore the potential of hyperspectral imaging as an approach to non-destructively and non-invasively quantify stress detection in insects and other animals.

Hydrocarbon profiles throughout adult Calliphoridae aging: A promising tool for forensic entomology

Blow flies (Diptera: Calliphoridae) are typically the first insects to arrive at human remains and carrion. Predictable succession patterns and known larval development of necrophagous insects on vertebrate remains can assist a forensic entomologist with estimates of a minimum post-mortem interval (PMImin) range. However, adult blow flies are infrequently used to estimate the PMImin, but rather are used for a confirmation of larval species identification. Cuticular hydrocarbons have demonstrated potential for estimating adult blow fly age, as hydrocarbons are present throughout blow fly development, from egg to adult, and are stable structures. The goal of this study was to identify hydrocarbon profiles associated with the adults of a North American native blow fly species, Cochliomyia macellaria (Fabricius) and a North American invasive species, Chrysomya rufifacies (Macquart). Flies were reared at a constant temperature (25°C), a photoperiod of 14:10 (L:D) (h), and were provided water, sugar and powdered milk ad libitum. Ten adult females from each species were collected at day 1, 5, 10, 20, and 30 post-emergence. Hydrocarbon compounds were extracted and then identified using gas chromatography-mass spectrometry (GC-MS) analysis. A total of 37 and 35 compounds were detected from C. macellaria and Ch. rufifacies, respectively. There were 24 and 23 n-alkene and methyl-branched alkane hydrocarbons from C. macellaria and Ch. rufifacies, respectively (10 compounds were shared between species), used for statistical analysis. Non-metric multidimensional scaling analysis and permutational multivariate analysis of variance were used to analyze the hydrocarbon profiles with significant differences (P<0.001) detected among post-emergence age cohorts for each species, and unique hydrocarbon profiles detected as each adult blow fly species aged. This work provides empirical data that serve as a foundation for future research into improving PMImin estimates made by forensic practitioners and potentially increase the use of adult insects during death investigations.

Age-dependent changes in cuticular hydrocarbons of larvae in Aldrichina grahami (Aldrich) (Diptera: Calliphoridae)

Necrophagous flies, comprising the first wave of insects present in a cadaver, provide a great potential for more accurate determination of the late postmortem interval (PMI) based on their age. Cuticular hydrocarbons (CHs) are a promising age indicator in some insect species, especially for the larvae of necrophagous flies. Gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) were used to characterize the age-dependent, quantitative changes in CHs of larval Aldrichina grahami (Aldrich) (Diptera: Calliphoridae) at 24°C. The majority of low-molecular-weight alkanes (≤C25) and almost all of the alkenes decreased in abundance with larval development. By contrast, the abundance of high-molecular-weight alkanes of chain length greater than C25 gradually increased with age. For several peaks, including peak 28 (pentacosene a), peak 31 (n-C25), peak 43 (n-C27) and peak 68 (n-C31), a highly significant correlation was found between peak ratio (n-C29 divided by each chromatographic peak) and chronological age of the larvae. A mathematical model, derived from multivariate linear regression analysis, was developed for determining age of the larvae based on age-dependent changes in CHs. The estimated larval age based on the CHs had a good linear correlation with the chronological age (R(2)>0.9). These results indicate that CHs has a great potential for determining the age of fly larvae, and concomitantly for the PMI in forensic investigation.

Identifying 1st instar larvae for three forensically important blowfly species using "fingerprint" cuticular hydrocarbon analysis

Calliphoridae are known to be the most forensically important insects when it comes to establishing the minimum post mortem interval (PMImin) in criminal investigations. The first step in calculating the PMImin is to identify the larvae present to species level. Accurate identification which is conventionally carried out by morphological analysis is crucial because different insects have different life stage timings. Rapid identification in the immature larvae stages would drastically cut time in criminal investigations as it would eliminate the need to rear larvae to adult flies to determine the species. Cuticular hydrocarbon analysis on 1st instar larvae has been applied to three forensically important blowflies; Lucilia sericata, Calliphora vicina and Calliphora vomitoria, using gas chromatography-mass spectrometry (GC-MS) and principal component analysis (PCA). The results show that each species holds a distinct "fingerprint" hydrocarbon profile, allowing for accurate identification to be established in 1-day old larvae, when it can be challenging to apply morphological criteria. Consequently, this GC-MS based technique could accelerate and strengthen the identification process, not only for forensically important species, but also for other entomological samples which are hard to identify using morphological features.

Reflectance-based identification of parasitized host eggs and adult Trichogramma specimens

A wide range of imaging and spectroscopy technologies is used in medical diagnostics, quality control in production systems, military applications, stress detection in agriculture, and ecological studies of both terrestrial and aquatic organisms. In this study, we hypothesized that reflectance profiling can be used to successfully classify animals that are otherwise very challenging to classify. We acquired hyperspectral images from adult specimens of the egg parasitoid genus Trichogramma (T. galloi, T. pretiosum and T. atopovirilia), which are ~1.0 mm in length. We also acquired hyperspectral images from host eggs containing developing Trichogramma instar and pupae. These obligate egg endoparasitoid species are commercially available as natural enemies of lepidopteran pests in food production systems. Because of their minute size and physical resemblance, classification is time consuming and requires a high level of technical experience. The classification of reflectance profiles was based on a combination of average reflectance and variogram parameters (describing the spatial structure of reflectance data) of reflectance values in individual spectral bands. Although variogram parameters (variogram analysis) are commonly used in large-scale spatial research (i.e. geoscience and landscape ecology), they have only recently been used in classification of high-resolution hyperspectral imaging data. The classification model of parasitized host eggs was equally successful for each of the three species and was successfully validated with independent data sets (>90% classification accuracy). The classification model of adult specimens accurately separated T. atopovirilia from the other two species, but specimens of T. galloi and T. pretiosum could not be accurately separated. Interestingly, molecular-based classification (using the DNA sequence of the internally transcribed spacer ITS2) of Trichogramma species published elsewhere corroborates the classification, as T. galloi and T. pretiosum are closely related and comparatively distant from T. atopovirilia. Our results emphasize the importance of using high-spectral and high-spatial resolution data in the classification of organism relatedness, and hyperspectral imaging may be of relevance to a wide range of commercial (i.e. producers of biocontrol agents), taxonomic and evolutionary research applications.

Cuticular hydrocarbons as a tool for the identification of insect species: puparial cases from Sarcophagidae

The external surface of all insects is covered by a species-specific complex mixture of highly stable, very long chain cuticular hydrocarbons (CHCs). Gas chromatography coupled to mass spectrometry was used to identify CHCs from four species of Sarcophagidae, Peckia (Peckia) chrysostoma, Peckia (Pattonella) intermutans, Sarcophaga (Liopygia) ruficornis and Sarcodexia lambens. The identified CHCs were mostly a mixture of n-alkanes, monomethylalkanes and dimethylalkanes with linear chain lengths varying from 23 to 33 carbons. Only two alkenes were found in all four species. S. lambens had a composition of CHCs with linear chain lengths varying from C23 to C33, while the other three species linear chain lengths from 24 to 31 carbons. n-Heptacosane, n-nonacosane and 3-methylnonacosane, n-triacontane and n-hentriacontane occurred in all four species. The results show that these hydrocarbon profiles may be used for the taxonomic differentiation of insect species and are a useful additional tool for taxonomic classification, especially when only parts of the insect specimen are available.

GC-MS analysis of cuticular lipids in recent and older scavenger insect puparia. An approach to estimate the postmortem interval (PMI)

An analytical method was developed to characterize puparia cuticular lipids (hydrocarbons, waxes) and to compare the molecular distribution patterns in the extracts from either recent or older puparia. Acid-catalyzed transesterification and solvent extraction and purification, followed by combined gas chromatography coupled to mass spectrometry, were optimized for the determination of hydrocarbons and fatty acid ethyl esters from transesterified waxes, extracted from a single species of a fly scavenger (Hydrotaea aenescens Wiedemann, 1830). Comparison between recent (2012) or older (1997) puparia contents has highlighted significant composition differences, in particular, a general decrease of the chain length in the n-alkane distribution pattern and, on the contrary, an increase of the ester chain length. Both extracts contain traces of three hopane hydrocarbon congeners. Preliminary results evidence the change in puparia lipid composition over time, thus potentially providing new indices for estimating postmortem interval.

Free fatty acids in the cuticular and internal lipids of Calliphora vomitoria and their antimicrobial activity

The cuticular and internal lipid composition in Calliphora vomitoria larvae, pupae, and male and female adults was studied. The free fatty acid (FA) compositions of the lipids were chemically characterized using gas chromatography (GC) and gas chromatography-electron impact mass spectrometry (GC-MS). Analyses of cuticular extracts from larvae, pupae, and male and female adults revealed that the carbon numbers of the acids ranged from C7:0 to C22:0, from C8:0 to C24:0, from C7:0 to C24:0 and from C7:0 to C22:0 respectively. The internal lipids of C. vomitoria larvae, pupae, male and female adults contained FAs ranging from C8:0 to C20:0, from C9:0 to C22:0, from C8:0 to C24:0 and from C9:0 to C22:0 respectively. Nine FAs with odd-numbered carbon chains from C7:0 to C21:0 were identified in the cuticular lipids of the larvae. The internal lipids of C. vomitoria larvae contained 8 odd-numbered FAs ranging from C9:0 to C19:0. Eight odd-numbered FAs from C9:0 to C21:0 were identified in the cuticular and internal lipids of pupae, while nine such FAs were found in the cuticular lipids of male and female adults. The internal lipids of adult males and females respectively contained nine and seven odd-numbered FAs, while both larvae and pupae contained eight such compounds. Eight unsaturated FAs were identified in the cuticular lipids of larvae, adult males and females and also in the internal lipids of females. Seven unsaturated FAs were identified in the cuticular lipids of pupae. The internal lipids of larvae, pupae and males contained 10, 11 and 12 unsaturated FAs respectively. Developmental changes were found both in the amounts of extracted cuticular and internal FAs and in their profiles. Four cuticular FAs (C7:0, C9:0, C10:0 and C15:1), identified as being male-specific, were either absent in the female cuticle or present there only in trace amounts. Cuticular and internal extracts obtained from larvae, pupae, adult males and females were tested for their potential antimicrobial activity. The minimal inhibitory concentrations of extracts against reference strains of bacteria and fungi were determined. Antimicrobial activity was the strongest against Gram-positive bacteria; Gram-negative bacteria, on the other hand, turned out to be resistant to all the lipids tested. Overall, the activities of the internal lipids were stronger. All the lipid extracts were equally effective against all the fungal strains examined. In contrast, crude extracts containing both cuticular and internal lipids displayed no antifungal activity against the entomopathogenic fungus Conidiobolus coronatus, which efficiently killed adult flies, but not larvae or pupae.