When, during ontogeny, waxes in the blowfly (Calliphoridae) cuticle can act as phylogenetic markers

The Entomo-Toxicological Effect Of Dichlorvos on Cuticular Hydrocarbon Profiles of Some Sarco-Saprophagous Insects for Forensic Applications

Forensic entomology has relied on species-specificity, quantitative and qualitative variations of cuticular hydrocarbons to successfully carry out chemotaxonomic identification of insects based on species, age and gender. This work studied the effects of dichlorvos on the cuticular hydrocarbon profiles of some adult sarco-saprophagous insects of forensic importance that fed on dichlorvos-poisoned carrions for utility during death investigations. Cuticular hydrocarbons (CHCs) were extracted from adult insects of the species Chrysomya albiceps, Sarcophaga exuberans, Musca domestica, Hermetia illucens, Dermestes maculatus and Necrobia rufipes from both dichlorvos-poisoned and control pig (Sus scrofa Linnaeus) carrions and subjected to chemotaxonomic profiling using Gas Chromatography-Mass Spectrometry (GC-MS). A total of 41 CHCs were successfully identified from insects of both the dichlorvos-poisoned and control carrions ranging from C8 to C33 carbons consisting of majorly the n-alkanes, methyl branched alkanes and an alkene. There was a higher abundance of CHCs present in the insects of dichlorvos-poisoned carrions than the control group. The highest mean peak concentration and abundance of the CHCs was recorded by 2,6,10,14 -Tetramethyl Pentadecane (10.38 ± 0.53 μg/mg for dichlorvos-poisoned carrions and 8.99 ± 1.13 μg/mg for the control carrions). The visualization of the species-specific differences in CHCs compositions showed less overlapping CHCs clusters and quantitative metrics of principal component analysis plots of the insects from both carrion groups with high eigenvalues > 3 which were indications of good species level discrimination. The study showed that insects' CHCs profiles of dichlorvos-poisoned and control carrions exhibited uniqueness cum variations in terms of abundance and chemical identity.

Molecular and Chemical Markers to Illustrate the Complex Diversity of the Genus Lupinus (Fabaceae)

The potential of secondary metabolites as systematic markers to get new insights in an intricate phylogeny of a recent evolutionary radiation is explored. A chemosystematic study of the genus Lupinus (Fabaceae) was performed, using quinolizidine (QA) and piperidine alkaloids (ammodendrine) as diagnostic characters. Seven major QA and the piperidine alkaloid ammodendrine were found to be the most frequent compounds. Two groups were supported according to their geographic origin: an Old World/Atlantic American group and a West New World group and this pattern is concordant with molecular data (here, based on an original barcode approach using the nuclear marker ITS). However, QA profiles are less informative at the species level. Despite a lack of resolution within the two groups, the alkaloid profiles agree with well supported clades based on DNA molecular characters. The combined use of chemical and barcode genetic markers represents a viable alternative for separating recent evolutionary lineages to a first approximation without having to resort to an expensive and sophisticated molecular arsenal such as next generation sequencing.

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.

New approach to application of mid-infrared photoacoustic spectroscopy in forensic analysis: Study with the necrophagous blow fly Chrysomya megacephala (Diptera: Calliphoridae)

Insects can provide clues in a variety of ways to assist in criminal investigations. The FTIR-PAS technique has been successfully used to assess the cuticular chemical profiles of insect samples from different groups and for several goals. However, until now, it has never been used to evaluate samples of forensic interest, despite providing faster results, compared to the methods currently used. In this study, mid-infrared photoacoustic spectroscopy was employed to assess the cuticular chemical profiles of different stages of development of the blow fly Chrysomya megacephala sampled from two distinct populations. The results showed that this technique enabled detection of significant differences between the main vibrational modes of the chemical bonds present in the cuticles of the two populations and the different stages of development of the fly. The method enables identification of the age of individuals collected at the crime scene, as well as the distinction of different populations. Therefore, this methodology could assist in forensic investigations, in both estimating the Postmortem Interval and determining the location where the crime occurred, or whether the body had suffered some type of translocation. The technique provides high reproducibility and fast analysis, so its application for analysis of C. megacephala is a viable option in forensic crime investigations.

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.

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.

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.

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.

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.

The antifungal activity of the cuticular and internal fatty acid methyl esters and alcohols in Calliphora vomitoria

SUMMARY The composition of the fatty acid methyl ester (FAME) and alcohol fractions of the cuticular and internal lipids of Calliphora vomitoria larvae, pupae and male/female adults was obtained by separating these two fractions by HPLC-LLSD and analysing them quantitatively using GC-MS. Analysis of the cuticular lipids of the worldwide, medically important ectoparasite C. vomitoria revealed 6 FAMEs with odd-numbered carbon chains from C15:0 to C19:0 in the larvae, while internal lipids contained 9 FAMEs ranging from C15:1 to C19:0. Seven FAMEs from C15:0 to C19:0 were identified in the cuticular lipids of the pupae, whereas the internal lipids of the pupae contained 10 FAMEs from C13:0 to C19:0. The cuticular lipids of males and females and also the internal lipids of males contained 5, 7 and 6 FAMEs from C15:0 to C19:0 respectively. Seven FAMEs from C13:0 to C19:0 were identified in the internal lipids of females, and 7, 6, 5 and 3 alcohols were found in the cuticular lipids of larvae, pupae, males and females respectively. Only saturated alcohols with even-numbered carbon chains were present in these lipids. Only 1 alcohol (C22:0) was detected in the internal lipids of C. vomitoria larvae, while just 4 alcohols from - C18:0 to C24:0 - were identified in the internal lipids of pupae, and males and females. We also identified glycerol and cholesterol in the larvae, pupae, males and females of C. vomitoria. The individual alcohols and FAMEs, as well as their mixtures isolated from the cuticular and internal lipids of larvae, pupae, males and females of C. vomitoria, demonstrated antimicrobial activity against entomopathogenic fungi.

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

The ontogeny of the cuticular hydrocarbons of three dipterans of importance to forensic entomology, Calliphora vomitoria (Linné), Calliphora vicina (Robineau-Desvoidy) and Protophormia terraenovae (Robineau-Desvoidy) (Diptera: Calliphoridae), was explored using gas chromatography analysis. The stages examined ranged from eggs to 8-day-old adults. Cuticular hydrocarbon profiles revealed that odd linear alkanes dominate in all three species. Short-chain carbon compounds in larvae and post-feeding larvae were seen to evolve to long-chain carbon compounds in pupae and adults. Discriminant analysis of cuticular hydrocarbon profiles showed a clear differentiation among the different stages (larvae, post-feeding larvae, pupae and adults) and within stages, according to the age of individuals. This study concluded that the postmortem interval can be determined from the composition of cuticular waxes in Calliphoridae in forensic situations.

Cuticular hydrocarbons are heritable in the cricket Teleogryllus oceanicus

The ability of individuals to respond differentially to conspecifics depending on their genetic relatedness is a widespread phenomenon across the animal kingdom. Despite this, little is known about the selection processes that act on the phenotypic variation of traits used during recognition. Here we use a quantitative genetic approach to examine the patterns of genetic variation in cuticular hydrocarbon (CHC) profiles, a pheromonal system used extensively in insect communication. Using gas chromatography, we found family specificity in the CHC profiles of male crickets, Teleogryllus oceanicus. Across CHC peaks, our mean coefficient of additive genetic variation was 10.8%. Multivariate principal component analysis showed that most axes of variation were weighted by CHC peaks with significant additive genetic variation. Our results provide evidence that variation in CHC profiles can reflect genetic relatedness, supporting the widely held belief that this phenotypic trait is used as a mechanism for chemosensory kin recognition.

Development changes of cuticular hydrocarbons in Chrysomya rufifacies larvae: potential for determining larval age

Age determination is the basis of determining the postmortem interval using necrophagous fly larvae. To explore the potential of using cuticular hydrocarbons for determining the ages of fly larvae, changes of cuticular hydrocarbons in developing larvae of Chrysomya rufifacies (Macquart) (Diptera: Calliphoridae) were investigated using gas chromatography with flame-ionization detection and gas chromatography-mass spectrometry. This study showed that the larvae produced cuticular hydrocarbons typical of insects. Most of the hydrocarbons identified were alkanes with the carbon chain length of 21-31, plus six kinds of alkenes. The hydrocarbon composition of the larvae correlated with age. The statistical results showed that simple peak ratios of n-C29 divided by another eight selected peaks increased significantly with age; their relationships with age could be modelled using exponential or power functions with R(2) close to or > 0.80. These results suggest that cuticular hydrocarbon composition is a useful indicator for determining the age of larval C. rufifacies, especially for post-feeding larvae, which are difficult to differentiate by morphology.