Looking into the puparium: Micro-CT visualization of the internal morphological changes during metamorphosis of the blow fly, Calliphora vicina, with the first quantitative analysis of organ development in cyclorrhaphous dipterans

An effective method for preparing histological sections of blow fly intra-puparial stages for minimum PMI estimations

Blow flies (Diptera: Calliphoridae) are generally early colonisers of fresh cadavers, enabling the estimation of a minimum post-mortem interval (minPMI) based on an accurate aging of the oldest immature stages associated with a cadaver. In blow flies, the pupal stage and the subsequent development of the adult take place inside a protective case, the puparium, formed from the hardened and darkened cuticle of the third instar larva. Because the puparium is an opaque structure that shows virtually no external changes, qualitative analyses of the internal tissues can be very informative for determining reliable age-specific morphological markers. Those analyses can be performed using either non-invasive but expensive and not widely accessible techniques, or traditional histological methods, which are invasive as they require the serial sectioning of the sample. Histological methods are often readily available for forensic researchers and practitioners; however, the histological study of blow fly intra-puparial stages has traditionally been hampered by the poor paraffin infiltration of tissues due to the abundance of fat bodies, resulting in usually fragmented sections and the subsequent loss of relevant information. We present here an effective method for the preparation of histological sections of blow fly intra-puparial stages, maximising the paraffin infiltration while enabling the production of clean and entire sections that allow for the use of reliable age-specific morphological markers, thus improving the accuracy of minPMI estimations when access to more costly techniques is not feasible.

A methodological approach to age estimation of the intra-puparial period of the forensically relevant blow fly Calliphora vicina via Fourier transform infrared spectroscopy

Estimating the age of immature blow flies is of great importance for forensic entomology. However, no gold-standard technique for an accurate determination of the intra-puparial age has yet been established. Fourier transform infrared (FTIR) spectroscopy is a method to (bio-)chemically characterise material based on the absorbance of electromagnetic energy by functional groups of molecules. In recent years, it also has become a powerful tool in forensic and life sciences, as it is a fast and cost-effective way to characterise all kinds of material and biological traces. This study is the first to collect developmental reference data on the changes in absorption spectra during the intra-puparial period of the forensically important blow fly Calliphora vicina Robineau-Desvoidy (Diptera: Calliphoridae). Calliphora vicina was reared at constant 20°C and 25°C and specimens were killed every other day throughout their intra-puparial development. In order to investigate which part yields the highest detectable differences in absorption spectra throughout the intra-puparial development, each specimen was divided into two different subsamples: the pupal body and the former cuticle of the third instar, that is, the puparium. Absorption spectra were collected with a FTIR spectrometer coupled to an attenuated total reflection (ATR) unit. Classification accuracies of different wavenumber regions with two machine learning models, i.e., random forests (RF) and support vector machines (SVMs), were tested. The best age predictions for both temperature settings and machine learning models were obtained by using the full spectral range from 3700 to 600 cm-1. While SVMs resulted in better accuracies for C. vicina reared at 20°C, RFs performed almost as good as SVMs for data obtained from 25°C. In terms of sample type, the pupal body gave smoother spectra and usually better classification accuracies than the puparia. This study shows that FTIR spectroscopy is a promising technique in forensic entomology to support the estimation of the minimum post-mortem interval (PMImin), by estimating the age of a given insect specimen.

Influence of photoperiod on the developmental times of the forensically relevant blow fly species Calliphora vicina (Diptera: Calliphoridae)

Blow flies (Diptera: Calliphoridae) are frequently used in forensic investigations due to their rapid colonization of cadavers. As with other insects, environmental temperature strongly influences their developmental rates. While published research has typically explored not only the impact of the environmental temperature, but also of other factors like tissue type and drug presence on developmental rates, the influence of photoperiod on the developmental rates of forensically relevant blow fly species has remained largely underexplored. Understanding the relationship between photoperiod and developmental times is crucial, as neglecting this aspect could compromise the accuracy of minimum post-mortem interval (minPMI) estimations. The present study investigates the impact of three photoperiod conditions (0:24, 8:16, and 12:12 light:darkness) on the developmental rates of Calliphora vicina, focusing on the duration of the different immature stages and on the total developmental time. Our results revealed significant variation in the intra-puparial stage and total development time across different photoperiods. Notably, a 12:12 photoperiod led to a significantly prolonged intra-puparial stage and total development time compared to the 0:24 photoperiod, suggesting that Calliphora vicina develops faster in total darkness. These findings highlight the importance of considering photoperiod in both laboratory rearing protocols and forensic casework to improve the accuracy and reliability of minPMI estimations. In this regard, preliminary guidelines and recommendations are provided.

Methods for the optimal preservation of blow fly intra-puparial forms for morphological analysis in forensic casework

Accurate minimum post-mortem interval (minPMI) estimations often rely on a precise age determination of insect developmental stages, which is significantly influenced by environmental temperature. An optimal preservation of the entomological samples collected at crime scenes is pivotal for a reliable aging of immature insect samples. For blow flies (Diptera: Calliphoridae), the most widely used insect indicators in forensic investigations, an appropriate preservation of tissues is particularly important in the case of puparial samples because aging methods for intra-puparial forms usually depend on morphological analyses; however, although informative soft tissues and structures could be discoloured and/or distorted if they are not properly fixed, there is a lack of studies to assess different methods for the optimal preservation of intra-puparial forms collected in forensic investigations. The present study compares three preservation methods for intra-puparial forms of the blow fly Calliphora vicina Robineau-Desvoidy, 1830: (i) direct immersion into 80% ethanol, (ii) puncturing of the puparium and hot water killing (HWK) prior to preservation in 80% ethanol, and (iii) HWK without puncturing before preservation in 80% ethanol. External and internal morphological analyses of intra-puparial forms of different ages were conducted to assess the quality of preservation. The results indicate that direct immersion in ethanol led to poor preservation, affecting both external and internal tissues. Both methods with HWK resulted in a better preservation, but puncturing resulted, in some cases, in physical damage of the specimens. HWK without puncturing emerged as the optimal preservation method, consistently yielding high preservation scores for both external and internal morphological analyses. These findings have practical implications for forensic practitioners and emphasise the need for updating some published guidelines and protocols in forensic entomology.

Micro-CT data of complete metamorphosis process in Harmonia axyridis

Insect metamorphosis involves significant changes in insect internal structure and is thus a critical focus of entomological research. Investigating the morphological transformation of internal structures is vital to understanding the origins of adult insect organs. Beetles are among the most species-rich groups in insects, but the development and transformation of their internal organs have yet to be systematically documented. In this study, we have acquired a comprehensive dataset that includes 27 detailed whole-body tomographic image sets of Harmonia axyridis, spanning from the prepupal to the pupal stages. Utilizing this data, we have created intricate 3D models of key internal organs, encompassing the brain, ventral nerve cord, digestive and excretion systems, as well as the body wall muscles. These data documented the transformation process of these critical organs and correlations between the origin of adult and larval organs and can be used to enhance the understanding of holometabolous adult organ genesis and offers a valuable reference model for investigating complete metamorphosis in insects.

The Morphological Transformation of the Thorax during the Eclosion of Drosophila melanogaster (Diptera: Drosophilidae)

The model organism Drosophila melanogaster, as a species of Holometabola, undergoes a series of transformations during metamorphosis. To deeply understand its development, it is crucial to study its anatomy during the key developmental stages. We describe the anatomical systems of the thorax, including the endoskeleton, musculature, nervous ganglion, and digestive system, from the late pupal stage to the adult stage, based on micro-CT and 3D visualizations. The development of the endoskeleton causes original and insertional changes in muscles. Several muscles change their shape during development in a non-uniform manner with respect to both absolute and relative size; some become longer and broader, while others shorten and become narrower. Muscular shape may vary during development. The number of muscular bundles also increases or decreases. Growing muscles are probably anchored by the tissues in the stroma. Some muscles and tendons are absent in the adult stage, possibly due to the hardened sclerites. Nearly all flight muscles are present by the third day of the pupal stage, which may be due to the presence of more myofibers with enough mitochondria to support flight power. There are sexual differences in the same developmental period. In contrast to the endodermal digestive system, the functions of most thoracic muscles change in the development from the larva to the adult in order to support more complex locomotion under the control of a more structured ventral nerve cord based on the serial homology proposed herein.

The formation of a rolling larval chamber as the unique structural gall of a new species of cynipid gall wasps

Insect galls, which often have complex external and internal structures, are believed to have adaptive significance for the survival of insects inside galls. A unique internal structure was discovered in the gall of a new cynipid species, Belizinella volutum Ide & Koyama, sp. nov., where the larval chamber could roll freely in the internal air space of the gall. Observations of the live galls using micro-computed tomography (micro-CT) revealed its formation process. The larval chamber becomes isolated from the internal parenchyma soon after the gall reaches the maximum diameter and is able to roll as the internal air space is expanding from the surrounding parenchyma to the outer gall wall. The enemy hypothesis could partly explain the adaptive significance of the unique structure of the gall of B. volutum.

Morphological and molecular characterization of puparia of Piophilidae species of forensic relevance

Piophilidae are a small family of Diptera with a worldwide distribution and which are historically associated with human activities. In addition to their economic importance, piophilid larvae can also be of medical and legal relevance. Within a medicolegal context, piophilids are frequently associated with cadavers in advanced stages of decomposition, thus being potentially useful forensic indicators and they have been reported also from archaeo-funerary contexts. An accurate species identification is therefore an essential prerequisite to ensure the reliable analysis of insect material in medical, forensic and archaeological investigations. Identification of the adult piophilid flies is possible because of the availability of identification keys, in contrast immature insects, especially puparia, have been poorly investigated and described. In this paper, puparia of 11 species of forensic interest (Piophila casei, Piophila megastigmata, Parapiophila atrifrons, Parapiophila flavipes, Parapiophila vulgaris, Protopiophila litigata, Liopiophila varipes, Prochyliza nigrimana, Prochyliza xanthosoma and Stearibia nigriceps in subtribe Piophilina and Centrophlebomyia furcata in subtribe Thyreophorina) are described and a molecular analysis, based on the COI sequencing, is presented to show the potential of the molecular approach in their identification.

Visualising fat reserves in an insect: A method using X-ray micro-computerised tomography of the Common Wasp (Vespula vulgaris)

The Common Wasp, Vespula vulgaris (Hymenoptera: Vespidae), has an annual nest cycle with new colonies initiated by over-wintered queens. Survival of adult queen wasps through winter dormancy is enabled through the deposition of substantial quantities of triglycerides in fat bodies. Worker (and male) wasps lack these fat reserves. By comparing micro-CT scans of workers, pre-hibernation queens and post-hibernation queens, we demonstrate that it is possible to semi-quantitatively measure fat reserves using arbitrary X-ray attenuation ranges. Venom in the venom gland of the queen wasps, has a significantly lower X-ray attenuation value than the triglyceride-rich fat bodies. This may be due to its content of low molecular weight volatile pheromones in addition to its other known constituents. We also demonstrate the utility of micro-CT for visualising a range of physiological and anatomical features of insects. This non-destructive method for measuring fat reserves can be used on appropriately preserved or freshly collected insect specimens.

Rethinking the ecdysteroid source during Drosophila pupal-adult development

Ecdysteroids, typified by 20-hydroxyecdysone (20E), are essential hormones for the development, reproduction and physiology of insects and other arthropods. For over half a century, the vinegar fly Drosophila melanogaster (Ephydroidea: Diptera) has been used as a model of ecdysteroid biology. Many aspects of the biosynthesis and regulation of ecdysteroids in this species are understood at the molecular level, particularly with respect to their secretion from the prothoracic gland (PG) cells of the ring gland, widely considered the dominant biosynthetic tissue during development. Discrete pulses of 20E orchestrate transitions during the D. melanogaster life cycle, the sources of which are generally well understood, apart from the large 20E pulse at the onset of pharate adult development, which has received little recent attention. As the source of this pharate adult pulse (PAP) is a curious blind spot in Drosophila endocrinology, we evaluate published biochemical and genetic data as they pertain to three hypotheses for the source of PAP 20E: the PG; an alternative biosynthetic tissue; or the recycling of stored 20E. Based on multiple lines of evidence, we contend the PAP cannot be derived from biosynthesis, with other data consistent with D. melanogaster able to recycle ecdysteroids before and during metamorphosis. Published data also suggest the PAP is conserved across Diptera, with evidence for pupal-adult ecdysteroid recycling occurring in other cyclorrhaphan flies. Further experimental work is required to test the ecdysteroid recycling hypothesis, which would establish fundamental knowledge of the function, regulation, and evolution of metamorphic hormones in dipterans and other insects.

Dynamic monitoring of vital functions and tissue re-organization in Saturnia pavonia (Lepidoptera, Saturniidae) during final metamorphosis by non-invasive MRI

Magnetic resonance imaging (MRI) is the key whole-body imaging technology for observing processes within a living object providing excellent resolution and contrast between soft tissues. In the present work, we exploited the non-destructive properties of MRI to track longitudinally the dynamic changes that take place in developing pupae of the Emperor Moth (Saturnia pavonia) during the last days before eclosion. While in diapause pupae, body fluid was almost homogeneously distributed over the internal compartments, as soon as wings, legs, flight muscles and the head region were fully developed, a significant redistribution of water levels occurred between thoracic and abdominal regions. During the last two days before eclosion, the developing moths transferred substantial amounts of liquid into the gut and the labial gland, and in case of females, into developing eggs. Concomitantly, the volume of the air sacs increased drastically and their expansion/compression became clearly visible in time-resolved MR images. Furthermore, besides ventilation of the tracheal system, air sacs are likely to serve as volume reservoir for liquid transfer during development of the moths inside their pupal case. In parallel, we were able to monitor noninvasively lipid consumption, cardiac activity and haemolymph circulation during final metamorphosis.

An X-ray micro-computer tomography study of the Malpighian tubules of the Blue Bottle Blow Fly (Calliphora vomitoria) Diptera: Calliphoridae

Malpighian tubules are the insect equivalent of mammalian kidneys and normally drain into the gut at the junction between the mid and hind gut. The Malpighian tubules of the fruit fly Drosophila melanogaster are increasingly being used as a model for studying human renal tract development, histology, nephrolithiasis and urolithiasis. In the present study we report when using X-ray micro-computer tomography techniques, the larval, intrapuparial and adult stages of the larger Calliphora vomitoria can contain large amounts of calcium-rich concretions which are tightly packed in the lumen of both anterior Malpighian tubules. We show that it is feasible to utilise these calcium-rich concretions as a form of marking agent to delineate the various developmental stages of the Malpighian tubules including the crucial phase when the Malpighian tubules reconnect with the hind gut. In the majority of cases during the intrapuparial period the ureters of the Malpighian tubules did not start to re-canalise and thus reconnect with the developing hind gut until the 7^th day of the 10-11 day. Just prior to ecdysis, virtually all the radio-opaque concretions in the Malpighian tubules had emptied into the hind gut and had then been completely excreted by the time the imago emerged from its puparium. In contrast, we show that in flies developing from larvae previously stained by ingesting Rhodamine B, a known substrate for both the Multi Xenobiotic Resistance and Multi Drug Resistant membrane transport systems, the efficiency with which these calcium-rich concretions are excreted by the imago as it emerges from its intrapuparial period can be significantly impaired. Therefore, it might be useful to include C. vomitoria as a model when studying renal tract development and urolithiasis using X-ray micro-computer tomography.

An examination of the intrapuparial development of Chrysomya albiceps (Wiedemann, 1819) (Calliphoridae: Diptera) at three different temperatures

The determination of intrapuparial development periods and development times of insects with holometabolous metamorphosis is necessary both in terms of developmental biology and for minimum Post-mortem interval (PMImin) calculations in forensic entomology. In this study, Chrysomya albiceps (Wiedemann, 1819), which is a cosmopolitan species and one of the most rapidly attracted to carrion, was studied. The focus was the intrapuparial development periods of this species at varying temperatures (20, 25, and 30 °C), knowledge which is used in forensic entomology for the estimation of Post-mortem interval (PMI) and is a type of black box. At the specified temperatures, pupae were collected and puparia were dissected hourly; thus, developmental periods were determined, and minimum and maximum starting times of these periods were calculated. With this research, a total of 20 periods, nine of which are new, were determined. The hourly determination of intrapuparial development periods at three different temperatures is the first in the world for this species.

Micro-CT imaging of Onchocerca infection of Simulium damnosum s.l. blackflies and comparison of the peritrophic membrane thickness of forest and savannah flies

Onchocerciasis is a neglected tropical disease (NTD) caused by Onchocerca Diesing 1841 (Spirurida: Onchocercidae) nematodes transmitted by blackflies. It is associated with poverty and imposes a significant health, welfare and economic burden on many tropical countries. Current methods to visualize infections within the vectors rely on invasive methods. However, using micro-computed tomography techniques, without interference from physical tissue manipulation, we visualized in three dimensions for the first time an L1 larva of an Onchocerca species within the thoracic musculature of a blackfly, Simulium damnosum s.l. Theobald 1903 (Diptera: Simuliidae), naturally infected in Ghana. The possibility that thicker peritrophic membranes in savannah flies could account for their lower parasite loads was not supported, but there were limits to our analysis. While there were no statistically significant differences between the mean thicknesses of the peritrophic membranes, in the anterior, dorsal and ventral regions, of forest and savannah blackflies killed 34-48 min after a blood-meal, the thickness of the peritrophic membrane in the posterior region could not be measured. Micro-computed tomography has the potential to provide novel information on many other parasite/vector systems and impactful images for public engagement in health education.

Micro-CT visualization of a promastigote secretory gel (PSG) and parasite plug in the digestive tract of the sand fly Lutzomyia longipalpis infected with Leishmania mexicana

Leishmaniasis is a debilitating disease of the tropics, subtropics and southern Europe caused by Leishmania parasites that are transmitted during blood feeding by phlebotomine sand flies (Diptera: Psychodidae). Using non-invasive micro-computed tomography, we were able to visualize the impact of the laboratory model infection of Lutzomyia longipalpis with Leishmania mexicana and its response to a second blood meal. For the first time we were able to show in 3D the plug of promastigote secretory gel (PSG) and parasites in the distended midgut of whole infected sand flies and measure its volume in relation to that of the midgut. We were also able to measure the degree of opening of the stomodeal valve and demonstrate the extension of the PSG and parasites into the pharynx. Although our pilot study could only examine a few flies, it supports the hypothesis that a second, non-infected, blood meal enhances parasite transmission as we showed that the thoracic PSG-parasite plug in infected flies after a second blood meal was, on average, more than twice the volume of the plug in infected flies that did not have a second blood meal.

Synchrotron X-ray phase contrast micro tomography to explore the morphology of abdominal organs in Pterostichus melas italicus Dejean, 1828 (Coleoptera, Carabidae)

Micro-computer tomography imaging is a fast and non-destructive data acquisition technique which can replace or complement the traditional investigation methodologies used in entomology to study morphology. In this paper, Synchrotron Radiation X-ray Phase-Contrast micro tomography (SR-PhC micro-CT) was combined with histology and scanning electron microscopy (SEM) observations to describe the abdominal organs of Pterostichus melas italicus Dejean, 1828 (Coleoptera, Carabidae). This species was used as a representative model because of its ecological role as a generalist predator in agroecosystems. SR-PhC micro-CT allowed us to identify in situ abdominal structures including dorsal vessel, digestive tract with Malpighian tubules, male reproductive system, ganglia, fat bodies, pygidial glands, muscles and tracheae. The histology was performed to define the tissue organization of the digestive and reproductive systems. SR-PhC micro-CT and 3D rendering provided more accurate information on shape and size of organs than histological and SEM analyses, respectively. The finding of this study was to describe the anatomy and histology of organs involved in crucial life history traits, such as reproduction, nutrition and excretion. High quality images and the supplementary video represent a significant advance in knowledge of the carabid anatomy and are a baseline for future research.

Major differences in the larval anatomy of the digestive and excretory systems of three Oestridae species revealed by micro-CT

Oestrid flies (Diptera: Oestridae) do not feed during the adult stage, so they depend on an efficient assimilation and storage of nutrients during their parasitic larval stage. We describe the general morphology and provide volumetric data for the digestive and excretory organs of the three larval instars of the nasal bot fly Oestrus ovis L., using micro-computed tomography. The size of the digestive and excretory organs greatly increased across larval instars. In all instars, the two salivary glands were remarkably large and formed a 'glandular band' by coming together, but without lumina uniting, at their posterior ends. The distal region of the anterior Malpighian tubules was greatly enlarged and full of highly radio-opaque concretions. Moreover, the anatomy of O. ovis third-instar larva was compared to that of two species of, respectively, similar and different feeding habits: Cephenemyia stimulator (Clark) and Hypoderma actaeon Brauer. Whereas the general morphology and arrangement of the digestive and excretory systems of C. stimulator was similar to that of O. ovis, some differences were observed in H. actaeon: a swollen anterior region of the midgut, salivary glands shorter and not forming a 'band' and anterior Malpighian tubules narrowly uniform throughout their entire length.

The Relationship between Research and Casework in Forensic Entomology

Simple Summary

Forensic entomology concerns the use of insects as evidence in legal investigations. Many sorts of investigation can benefit from an interpretation of insects associated with the crime scene, but insect evidence is most frequently used in investigations of death. The interpretation of insect evidence in casework is guided by the data supplied through research. Such data are essential to improve the casework interpretation of insect evidence, thereby improving the robustness of the legal systems in which it operates. This paper explores the mutually beneficial relationship between research and casework in forensic entomology, contrasting the different challenges that each presents and giving examples of how each can support the other in delivering results of real societal benefit. It is written from the perspective of the Criminal Justice System of England and Wales, but many of the points raised are relevant to legal systems worldwide.

Abstract

Research is a vital component of all forensic sciences and is often stimulated by casework, which identifies gaps in our knowledge. In such a niche area of forensic science as entomology there should be a close and mutually beneficial relationship between research and casework: to some extent there is a continuum between the two and many forensic entomologists are involved in both to a greater or lesser degree. However, research and casework involve quite differing challenges, from the replicated, highly controlled, sometimes esoteric aspects of research to the very individual, sometimes chaotic and disruptive, but highly applied aspects of casework. Ideally casework will include the full involvement of a forensic entomologist, who will collect the insect and climate evidence at the scene and produce a robust expert witness statement based on a full analysis of this data. Unfortunately, it can also include situations where samples, if collected at all, are poorly preserved, not representative of the full cadaver fauna available and presented to the entomologist months or years after the event, without local temperature data. While research is recognised through publications and their citation indices, casework and its associated expert witness statements often receive no credit in an academic workplace, although they do have a positive societal impact and many other benefits of teaching and public engagement value. This manuscript examines the relationship between research and casework from a UK perspective, to raise awareness of the need to create an environment that values the contribution of both, for future generations to flourish in both areas.

Evaluation of Reference Genes and Age Estimation of Forensically Useful Aldrichina grahami (Diptera: Calliphoridae) During Intrapuparial Period

The minimum postmortem interval (PMImin) could be evaluated from the developmental stage of forensically important insects colonize a corpse, such as blow flies (Diptera: Calliphoridae). Unlike larvae, the developmental stage of which is well established according to their morphology, estimating the age of pupae is proven to be challenging. Recently, several studies reported the regulation of special genes during the development of blow fly pupae. However, gene regulation in Aldrichina grahami during the intrapuparial period remains to be studied. Therefore, we set out to investigate the mRNA levels of heat shock protein 23 (Hsp23), heat shock protein 24 (Hsp24), and 1_16 during the metamorphosis of A. grahami pupae. First, we examined seven candidate reference genes (ribosomal protein 49 (RP49), 18S ribosomal RNA (18S rRNA), 28S ribosomal RNA (28S rRNA), beta-tubulin at 56D (β-tubulin), Ribosomal protein L23 (RPL23), glutathione S-transferase (GST1), and Actin. Three widely used algorithms (NormFinder, BestKeeper, and geNorm) were applied to evaluate the mRNA levels of reference gene candidates in puparium at three stable temperatures (15, 22, and 27°C). Next, mRNA expression of Hsp23, Hsp24, and 1_16 during A. grahami metamorphosis was examined. We demonstrated that mRNA expression levels of Hsp23, Hsp24, and 1_16 showed time-specific regulation. In summary, our study identified three gene markers for the intrapuparial period of A. grahami and might provide a potential application in PMImin estimation.

The effect of submersion in different types of water on the survival and eclosion of blow-fly intra-puparial forms (Diptera: Calliphoridae)

Blow-fly (Diptera: Calliphoridae) immatures are the main colonizers of decomposing remains, and any information on what influences their growth and development are important to forensic entomologists when they are required to estimate post-mortem intervals during a death investigation. Much of this work has been qualified and quantified in terrestrial environments, but is deplete in aquatic environments. When considering a blow-fly's life history, the longest immature life stage goes from the formation of the puparium to adult emergence, and involves metamorphosis. In an aquatic scenario a corpse may be completely submerged, floating on the surface and or it could be associated with water but neither submerged or floating (e.g. beached on a seashore or washed up after a flood event). The present study concerns two blow-fly species, Lucilia sericata (Meigen) and Calliphora vomitoria (L.), and the effects of the age of the intra-puparial forms ("pupal age") and resultant survival, when submerged in tap, river or salt water for varying times - up to 3 days. The experiment was conducted in two localities, L. sericata in Boston USA and C. vomitoria in Turin, Italy, and full puparia of both species were divided into 4 age cohorts ("white", "young", "medium", and "old') before submergence. L. sericata intra-puparial forms showed a three time greater survival rate compared to C. vomitoria intra-puparial forms when submerged in each of the three water types. Both species had the highest survival rate in tap water. Overall, younger and older intra-puparial forms showed a greater and significant survival rate than medium intra-puparial forms when submerged. The eclosion time following submersion of C. vomitoria and L. sericata was mainly influenced by both the age at which the intra-puparial forms were submerged, and by the type of water, but the duration of the submersion also influenced the eclosion time of L. sericata. These results are discussed considering blow-fly physiology. A deeper understanding of the dynamics of survival and growth rate of blow-fly intra-puparial forms on human remains that have undergone a period of submergence could assist in the estimation of the time of death in criminal cases connected to different aquatic environments.

Gene expression as age estimation marker in the larval stages of the forensic blowfly, Chrysomya albiceps, at different temperatures

The blowfly Chrysomya albiceps (Diptera: Calliphoridae) has been known to breed in both animal and human carcasses in different geographical regions and is considered an important post-mortem indicator in forensic entomology. Determining the age of its larvae is an essential tool for the accurate determination of post-mortem intervals (PMI). This study adopted a molecular-based approach for age determination of the immature stages of the blowfly, C. albiceps, by evaluating the genes 15_2, 2014192, EcdR, AR, hsp90, and Actin, during larval development at different temperatures. Targeted genes were amplified by real-time PCR (RT-PCR), and the resulting amplicons were normalized against the two housekeeping genes, rp49 and 19_2. Data showed that the expression profile of AR was constant throughout all larval developmental stages at all tested temperatures. 2014192 showed low expression levels throughout the 1st, 2nd, and 3rd larval stages. Hsp90 and EcdR showed different expression profiles. The expression of 15_2 was low at the tested temperatures and was undetectable on most days. Collectively, the results of this study indicate that larvae exhibit temperature-dependent and age-specific up- and down-regulation in the expression profile of the targeted genes. This may indicate a possibility to be utilized as age estimation markers for C. albiceps.

Internal morphological changes during metamorphosis in the sheep nasal bot fly, Oestrus ovis

During the larval stage, oestrid flies (Diptera: Oestridae) are obligate parasites, whereas during the adult stage they are free-living and do not feed. Like other cyclorrhaphous flies, oestrids undergo metamorphosis inside an opaque puparium, formed by the contracted and hardened cuticle of the third-instar larva. The present study documents the internal morphological changes taking place during metamorphosis of the sheep nasal bot fly, Oestrus ovis L., using non-invasive, micro-CT-based virtual histology and provides quantitative data of volumetric changes in specific organs. Virtual histological sections allowed visualisation of the progression and completion of the apolyses, which delimit the different intra-puparial stages, and the connection to the tracheal system of a large gas bubble, which plays an essential role during early metamorphosis. Overall, our results show that the sequence of morphological and volumetric changes in tissues and organs is similar to those found in other cyclorrhaphous flies, but they also reveal developmental differences that result in an adult vestigial digestive tract. Future studies could develop non-invasive, reliable methods for aging the intra-puparial forms of different oestrid species of veterinary importance, based on both qualitative and quantitative markers, thus improving our knowledge of their development and the efficiency of control strategies.

A morphological analysis of fresh and brine-cured olives attacked by <em>Bactrocera oleae</em> using light microscopy and ESEM-EDS

The present study investigated the morphology of fresh and brine-cured table olives (TOs) as well as the changes that occur when drupes are attacked by the fruit fly Bactrocera oleae. Morphological analyses were performed using light microscopy (LM) and environmental scanning electron microscopy coupled with energy dispersive spectroscopy (ESEM-EDS). The LM analysis was carried out with bright-field microscopy to evaluate sections stained with either PAS or Azan mixtures as well as unstained sections observed at fluorescence microscopy. The results of the analyses showed that: i) Azan and PAS staining played a useful complementary role, increasing the information provided by the histological analysis. Indeed, in both fresh and brine-cured TOs, epidermal layers and mesocarpal cells were clearly revealed, including sclereid cells. The histological analysis allowed also identifying the presence of secoiridoid-biophenols (seco-BPs) in both cell walls and vacuoles, as well as in the drupe regions that had been attacked by fruit flies, where they were found at higher concentrations; ii) In fresh and brine-cured olives, the excitation at 480 nm revealed the distribution of the fluorophores, among which the seco-BP are enclosed; iii) the ESEM-EDS analysis revealed the natural morphology of fresh olives, including the dimensions of their cell layers and the size and depth of the mechanical barriers of suberized or necrotic cells around the larva holes. In addition, the elemental composition of regions of interest of the drupe was determined in fresh and brine-cured TOs. The results highlighted the effectiveness of combined use of LM and ESEM-EDS in order to obtain a picture, as complete as possible, of the structural morphology of TOs. Such analytical combined approach can be used to support multidisciplinary studies aimed at the selection of new cultivars more resistant to fly attack.

Intra-puparial development in the hoverflies Eristalinus aeneus and Eristalis tenax (Diptera: Syrphidae)

The intra-puparial development of 150 pupae of Eristalinus aeneus (Scopoli, 1763) and Eristalis tenax (Linnaeus, 1758) was analyzed. Individuals were obtained from the sixth laboratory generation kept under artificial rearing conditions at the facilities of the University of Alicante (Spain). The experiment was conducted at 25 ± 1°C temperature, 50 ± 5% relative humidity, and 12:12 hr (L:D) of photoperiod. Groups of 10 pupae were collected every 6 hr over 48 hr, after that period, pupae were collected daily until the adult emergence. They were fixed in 5% formic acid and preserved in 70% ethanol. Fixed pupae were dissected and photographed. The chronology and morphological changes that take place during the intra-puparial development in both species were analyzed and compared. Five phases were observed: prepupa, before 6 hr; cryptocephalic pupa, between 6 and 24 hr; phanerocephalic pupa, between 24 and 30 hr; pharate adult, after 30 hr; and the adult imago, restricted to the very end of the development process just before adult emergence. In total, the intra-puparial development lasted 189 ± 4 hr in E. aeneus and 192 ± 3 hr in E. tenax, with the pharate adult the longest phase (some 81% of the total developmental time). These data can be used to develop accurate cold storage protocols during artificial rearing of both pollinator species, avoiding critical events during the development and increasing survival.

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.

A comprehensive and user-friendly framework for 3D-data visualisation in invertebrates and other organisms

Methods for 3D‐imaging of biological samples are experiencing unprecedented development, with tools such as X‐ray micro‐computed tomography (μCT) becoming more accessible to biologists. These techniques are inherently suited to small subjects and can simultaneously image both external and internal morphology, thus offering considerable benefits for invertebrate research. However, methods for visualising 3D‐data are trailing behind the development of tools for generating such data. Our aim in this article is to make the processing, visualisation and presentation of 3D‐data easier, thereby encouraging more researchers to utilise 3D‐imaging. Here, we present a comprehensive workflow for manipulating and visualising 3D‐data, including basic and advanced options for producing images, videos and interactive 3D‐PDFs, from both volume and surface‐mesh renderings. We discuss the importance of visualisation for quantitative analysis of invertebrate morphology from 3D‐data, and provide example figures illustrating the different options for generating 3D‐figures for publication. As more biology journals adopt 3D‐PDFs as a standard option, research on microscopic invertebrates and other organisms can be presented in high‐resolution 3D‐figures, enhancing the way we communicate science.

The utility of micro-computed tomography for the non-destructive study of eye microstructure in snails

Molluscan eyes exhibit an enormous range of morphological variation, ranging from tiny pigment-cup eyes in limpets, compound eyes in ark clams and pinhole eyes in Nautilus, through to concave mirror eyes in scallops and the large camera-type eyes of the more derived cephalopods. Here we assess the potential of non-destructive micro-computed tomography (µ-CT) for investigating the anatomy of molluscan eyes in three species of the family Solariellidae, a group of small, deep-sea gastropods. We compare our results directly with those from traditional histological methods applied to the same specimens, and show not only that eye microstructure can be visualised in sufficient detail for meaningful comparison even in very small animals, but also that μ-CT can provide additional insight into gross neuroanatomy without damaging rare and precious specimens. Data from μ-CT scans also show that neurological innervation of eyes is reduced in dark-adapted snails when compared with the innervation of cephalic tentacles, which are involved in mechanoreception and possibly chemoreception. Molecular tests also show that the use of µ-CT and phosphotungstic acid stain do not prevent successful downstream DNA extraction, PCR amplification or sequencing. The use of µ-CT methods is therefore highly recommended for the investigation of difficult-to-collect or unique specimens.

First Insights into the Intrapuparial Development of Bactrocera dorsalis (Hendel): Application in Predicting Emergence Time for Tephritid Fly Control

Intrapuparial development is a special pattern of metamorphosis in cyclorrhaphous flies, in which the pupa forms in an opaque, barrel-like puparium. This has been well studied in forensic insects for age estimations. In this study, the intrapuparial development of a quarantine agricultural pest, Bactrocera dorsalis (Hendel), was studied under a constant temperature of 27 ± 1 °C and 70 ± 5% relative humidity. Results showed that intrapuparial development could be divided into five stages: Larval-pupal apolysis, cryptocephalic pupa, phanerocephalic pupa, pharate adult, and emergent adult. It lays a morphology-based foundation for molecular mechanism studies and enhances the understanding of the physiological basis for changes in intrapuparial development. More importantly, the chronology of intrapuparial development can be used to predict the emergence time of tephritid flies, indicating when to spray insecticides to control these phytophagous agricultural pests. This may be an effective approach to reduce the use of insecticides and slow down the evolution of insecticidal resistance.

Visualization of insect metamorphosis

Metamorphosis and, in particular, holometaboly, the development of organisms through a series of discrete stages (egg, larva, pupa, adult) that hardly resemble one another but are finely adapted to specific roles in the life cycle of the organism, has fascinated and mystified humans throughout history. However, it can be difficult to visualize the dramatic changes that occur during holometaboly without destructive sampling, traditionally through histology. However, advances in imaging technologies developed mainly for medical sciences have been applied to studies of insect metamorphosis over the past couple of decades. These include micro-computed tomography, magnetic resonance imaging and optical coherence tomography. A major advantage of these techniques is that they are rapid and non-destructive, enabling virtual dissection of an organism in any plane by anyone who has access to the image files and the necessary software. They can also be applied in some cases to visualize metamorphosis in vivo, including the periods of most rapid and dramatic morphological change. This review focusses on visualizing the intra-puparial holometabolous metamorphosis of cyclorraphous flies (Diptera), including the primary model organism for all genetic investigations, Drosophila melanogaster, and the blow flies of medical, veterinary and forensic importance, but also discusses similar studies on other insect orders. This article is part of the theme issue 'The evolution of complete metamorphosis'.

Micro-computed tomography of pupal metamorphosis in the solitary bee Megachile rotundata

Insect metamorphosis involves a complex change in form and function. In this study, we examined the development of the solitary bee, Megachile rotundata, using micro-computed tomography (μCT) and volume analysis. We describe volumetric changes of brain, tracheae, flight muscles, gut, and fat bodies in prepupal, pupal, and adult M. rotundata. We observed that individual organ systems have distinct patterns of developmental progression, which vary in their timing and duration. This has important implications for commercial management of this agriculturally relevant pollinator.

Micro-computed tomography visualization of the vestigial alimentary canal in adult oestrid flies

Oestrid flies (Diptera: Oestridae) do not feed during the adult stage as they acquire all necessary nutrients during the parasitic larval stage. The adult mouthparts and digestive tract are therefore frequently vestigial; however, morphological data on the alimentary canal in adult oestrid flies are scarce and a proper visualization of this organ system within the adult body is lacking. The present work visualizes the morphology of the alimentary canal in adults of two oestrid species, Oestrus ovis L. and Hypoderma lineatum (de Villiers), with the use of non-invasive micro-computed tomography (micro-CT) and compares it with the highly developed alimentary canal of the blow fly Calliphora vicina Robineau-Desvoidy (Diptera: Calliphoridae). Both O. ovis and H. lineatum adults showed significant reductions of the cardia and the diameter of the digestive tract, an absence of the helicoidal portion of the midgut typical of other cyclorrhaphous flies, and a lack of crop and salivary glands. Given the current interest in the alimentary canal in adult dipterans in biomedical and developmental biology studies, further understanding of the morphology and development of this organ system in adult oestrids may provide valuable new insights in several areas of research.

Bioprospection of immature salivary glands of Chrysomya megacephala (Fabricius, 1794) (Diptera: Calliphoridae)

Larval therapy (LT) comprises the application of sterile Calliphoridae larvae for wound debridement, disinfection, and healing in humans and animals. Larval digestion plays a key role in LT, where the salivary glands and gut produce and secrete proteolytic and antimicrobial substances. The objective of this work was to bioprospect the salivary glands of Chrysomya megacephala (Fabricius, 1794) larvae, using ultrastructural, morphological, and histological observations, and the total protein electrophoretic profile. The salivary glands present a deferent duct, originating from the buccal cavity, which bifurcates into efferent ducts that insert through a slight dilatation to a pair of tubular-shaped tissues, united in the region of fat cells. Histologically, the secretion had protein characteristics. Cell cytoplasm presented numerous free ribosomes, autophagic vacuoles, spherical and elongated mitochondria, atypical Golgi complexes, and dilated rough endoplasmic reticulum. In the apical cytoplasm, secretory granules and microvilli secretions demonstrated intense protein synthesis, basal cytoplasm with trachea insertions, and numerous mitochondria. The present work described the ultrastructure and morphology of C. megacephala third instar salivary glands, confirming intense protein synthesis and the molecular weight of soluble proteins.

3D virtual histology at the host/parasite interface: visualisation of the master manipulator, Dicrocoelium dendriticum, in the brain of its ant host

Some parasites are able to manipulate the behaviour of their hosts to their own advantage. One of the most well-established textbook examples of host manipulation is that of the trematode Dicrocoelium dendriticum on ants, its second intermediate host. Infected ants harbour encysted metacercariae in the gaster and a non-encysted metacercaria in the suboesophageal ganglion (SOG); however, the mechanisms that D. dendriticum uses to manipulate the ant behaviour remain unknown, partly because of a lack of a proper and direct visualisation of the physical interface between the parasite and the ant brain tissue. Here we provide new insights into the potential mechanisms that this iconic manipulator uses to alter its host's behaviour by characterising the interface between D. dendriticum and the ant tissues with the use of non-invasive micro-CT scanning. For the first time, we show that there is a physical contact between the parasite and the ant brain tissue at the anteriormost part of the SOG, including in a case of multiple brain infection where only the parasite lodged in the most anterior part of the SOG was in contact with the ant brain tissue. We demonstrate the potential of micro-CT to further understand other parasite/host systems in parasitological research.

X-ray microtomography (microCT) of male genitalia of Nothybus kuznetsovorum (Nothybidae) and Cothornobata sp. (Micropezidae)

The results of manual dissection of the musculature of the male genitalia in Nothybuskuznetsovorum are fully confirmed by the modern methods of Micro-CT. A comparative analysis of Neriacommutata and Cothornobata sp. shows that an increase in the flexion in the genitalia of males and the displacement of syntergosternite VII to the ventral side in Cothornobata sp. caused the disappearance of the muscles ITM6–7r and ITM7–8r. In addition, this increase in flexion apparently caused the fusion of the M18 muscles into one bundle. The muscle ISM5-6c goes on to moving the second segment of the forcipate appendages of sternite V.

Dating Pupae of the Blow Fly Calliphora vicina Robineau-Desvoidy 1830 (Diptera: Calliphoridae) for Post Mortem Interval-Estimation: Validation of Molecular Age Markers

Determining the age of juvenile blow flies is one of the key tasks of forensic entomology when providing evidence for the minimum post mortem interval. While the age determination of blow fly larvae is well established using morphological parameters, the current study focuses on molecular methods for estimating the age of blow flies during the metamorphosis in the pupal stage, which lasts about half the total juvenile development. It has already been demonstrated in several studies that the intraspecific variance in expression of so far used genes in blow flies is often too high to assign a certain expression level to a distinct age, leading to an inaccurate prediction. To overcome this problem, we previously identified new markers, which show a very sharp age dependent expression course during pupal development of the forensically-important blow fly Calliphora vicina Robineau-Desvoidy 1830 (Diptera: Calliphoridae) by analyzing massive parallel sequencing (MPS) generated transcriptome data. We initially designed and validated two quantitative polymerase chain reaction (qPCR) assays for each of 15 defined pupal ages representing a daily progress during the total pupal development if grown at 17 °C. We also investigated whether the performance of these assays is affected by the ambient temperature, when rearing pupae of C. vicina at three different constant temperatures-namely 17 °C, 20 °C and 25 °C. A temperature dependency of the performance could not be observed, except for one marker. Hence, for each of the defined development landmarks, we can present gene expression profiles of one to two markers defining the mentioned progress in development.

Histological age estimation of the eggs of Calliphora vicina Robineau Desvoidy (Diptera: Calliphoridae)

Aging blow fly eggs can be critical to a forensic investigation, but there are currently no forensically useful timelines describing internal anatomical changes in embryological development. This is partly due to the lack of an economical, rapid and technically simple histological technique to allow mass production of slides for research and casework. We present a histological method that uses a slightly modified standard laboratory processing run with 1 h fixation in 10% formalin, 2 h softening in Molliflex and Haemotoxylin and Eosin (H&E) staining. We also present a summary of the internal anatomical changes that can be visualized using our technique in the developing eggs of Calliphora vicina Robineau-Desvoidy (Diptera: Calliphoridae). We examined eggs from at least three different females grown at 15 °C and sampled at 6 h intervals, and eggs grown at 20 °C and sampled at 3 h intervals. Blind aging trials demonstrated that it is possible to accurately age material grown at 20 °C to within 6 h (but attempts to further narrow this interval resulted in errors in one-third of cases). It was also possible to see sufficient anatomical detail to age eggs preserved for forensic casework 5, 8, 9, 10 and 11 years previously. Additionally, we determined that section quality was improved by 5 s fixation in hot water prior to preservation in ethanol. However, hot water fixation for longer than this increased the level of section artefact.

Initial investigations of spectral measurements to estimate the time within stages of Protophormia terraenovae (Robineau-Desvoidy) (Diptera: Calliphoridae)

Current applications of forensic entomology to post-mortem interval estimations involve ageing the insects colonizing the remains based on minimum time to reach the oldest stage of development. Immature species of blow fly develop at a predictable rate to each stage of development in their lifecycle. Unfortunately, the minimum time to reach a stage of development can be a rather unrefined estimate of tenure on the body in the sometimes lengthy time frame of the later stages. In a successful attempt to narrow this time frame, daily spectral measurements of the immature stages of Protophormia terraenovae (Robineau-Desvoidy) raised at a mean temperature of 24.6°C were collected and the functional data analysis was completed. Functional regressions and coefficient functions were examined for model prediction and generalization. P. terraenovae is a Holarctic species as well as an early colonizer of human remains and is therefore, an excellent indicator species in North American death investigations. Spectral measurements can be used successfully to estimate the day of development in the third instar including post feeding stage. In the intra-puparial period, however, only the last day of development could be distinguished from the earlier days of the intra-puparial period. Distinguishing day within second instar is also possible for P. terraenovae raised at a mean temperature of 24.6°C and, although not fully within the pointwise 95% confidence interval, it still accurately predicts the day. The results of this proof of concept research are promising and show a potential method for narrowing the original death estimates and offering a better overall estimate of age of P. terraenovae larvae and, therefore; estimated time since death.

Age estimation during the blow fly intra-puparial period: a qualitative and quantitative approach using micro-computed tomography

Minimum post-mortem interval (_minPMI) estimates often rely on the use of developmental data from blow flies (Diptera: Calliphoridae), which are generally the first colonisers of cadavers and, therefore, exemplar forensic indicators. Developmental data of the intra-puparial period are of particular importance, as it can account for more than half of the developmental duration of the blow fly life cycle. During this period, the insect undergoes metamorphosis inside the opaque, barrel-shaped puparium, formed by the hardening and darkening of the third instar larval cuticle, which shows virtually no external changes until adult emergence. Regrettably, estimates based on the intra-puparial period are severely limited due to the lack of reliable, non-destructive ageing methods and are frequently based solely on qualitative developmental markers. In this study, we use non-destructive micro-computed tomography (micro-CT) for (i) performing qualitative and quantitative analyses of the morphological changes taking place during the intra-puparial period of two forensically relevant blow fly species, Calliphora vicina and Lucilia sericata, and (ii) developing a novel and reliable method for estimating insect age in forensic practice. We show that micro-CT provides age-diagnostic qualitative characters for most 10% time intervals of the total intra-puparial period, which can be used over a range of temperatures and with a resolution comparable to more invasive and time-consuming traditional imaging techniques. Moreover, micro-CT can be used to yield a quantitative measure of the development of selected organ systems to be used in combination with qualitative markers. Our results confirm micro-CT as an emerging, powerful tool in medico-legal investigations.

Looking into the puparium: Micro-CT visualization of the internal morphological changes during metamorphosis of the blow fly, Calliphora vicina, with the first quantitative analysis of organ development in cyclorrhaphous dipterans

Metamorphosis of cyclorrhaphous flies takes place inside a barrel‐like puparium, formed by the shrinking, hardening and darkening of the third‐instar larval cuticle. The opacity of this structure hampers the visualization of the morphological changes occurring inside and therefore a full understanding of the metamorphosis process. Here, we use micro‐computed tomography (micro‐CT) to describe the internal morphological changes that occur during metamorphosis of the blow fly, Calliphora vicina Robineau‐Desvoidy 1830 (Diptera: Calliphoridae) at a greater temporal resolution than anything hitherto published. The morphological changes were documented at 10% intervals of the total intra‐puparial period, and down to 2.5% intervals during the first 20% interval, when the most dramatic morphological changes occur. Moreover, the development of an internal gas bubble, which plays an essential role during early metamorphosis, was further investigated with X‐ray images and micro‐CT virtual sections. The origin of this gas bubble has been largely unknown, but micro‐CT virtual sections show that it is connected to one of the main tracheal trunks. Micro‐CT virtual sections also provided enough resolution for determining the completion of the larval‐pupal and pupal‐adult apolyses, thus enabling an accurate timing of the different intra‐puparial life stages. The prepupal, pupal, and pharate adult stages last for 7.5%, 22.5%, and 70% of the total intra‐puparial development, respectively. Furthermore, we provide for the first time quantitative data on the development of two organ systems of the blow fly: the alimentary canal and the indirect flight muscles. There is a significant and negative correlation between the volume of the indirect flight muscles and the pre‐helicoidal region of the midgut during metamorphosis. The latter occupies a large portion of the thorax during the pupal stage but narrows progressively as the indirect flight muscles increase in volume during the development of the pharate adult.

The 'dance' of life: visualizing metamorphosis during pupation in the blow fly Calliphora vicina by X-ray video imaging and micro-computed tomography

The dramatic metamorphosis from larva to adult of insect orders such as Diptera cannot usually be witnessed because it occurs within an opaque structure. For the cyclorrhaphous dipterans, such as blow flies, this structure is the puparium, formed from the larval cuticle. Here, we reveal metamorphosis within the puparium of a blow fly at higher temporal resolution than previously possible with two-dimensional time-lapse videos created using the X-ray within a micro-computed tomography scanner, imaging development at 1 min and 2 min intervals. Our studies confirm that the most profound morphological changes occur during just 0.5% of the intrapuparial period (approx. equivalent to 1.25 h at 24°C) and demonstrate the significant potential of this technique to complement other methods for the study of developmental changes, such as hormone control and gene expression. We hope this will stimulate a renewed interest among students and researchers in the study of morphology and its astonishing transformation engendered by metamorphosis.

Non-destructive, high-content analysis of wheat grain traits using X-ray micro computed tomography

BACKGROUND

Wheat is one of the most widely grown crop in temperate climates for food and animal feed. In order to meet the demands of the predicted population increase in an ever-changing climate, wheat production needs to dramatically increase. Spike and grain traits are critical determinants of final yield and grain uniformity a commercially desired trait, but their analysis is laborious and often requires destructive harvest. One of the current challenges is to develop an accurate, non-destructive method for spike and grain trait analysis capable of handling large populations.

RESULTS

In this study we describe the development of a robust method for the accurate extraction and measurement of spike and grain morphometric parameters from images acquired by X-ray micro-computed tomography (μCT). The image analysis pipeline developed automatically identifies plant material of interest in μCT images, performs image analysis, and extracts morphometric data. As a proof of principle, this integrated methodology was used to analyse the spikes from a population of wheat plants subjected to high temperatures under two different water regimes. Temperature has a negative effect on spike height and grain number with the middle of the spike being the most affected region. The data also confirmed that increased grain volume was correlated with the decrease in grain number under mild stress.

CONCLUSIONS

Being able to quickly measure plant phenotypes in a non-destructive manner is crucial to advance our understanding of gene function and the effects of the environment. We report on the development of an image analysis pipeline capable of accurately and reliably extracting spike and grain traits from crops without the loss of positional information. This methodology was applied to the analysis of wheat spikes can be readily applied to other economically important crop species.