Effects of temperature and tissue type on Chrysomya rufifacies (Diptera: Calliphoridae) (Macquart) development

Development of the house fly, Musca domestica L. (Diptera: Muscidae), on pork tissue at two temperatures

The house fly, Musca domestica, L. (Diptera: Muscidae), is a filth fly that is often associated with criminal and civil investigations surrounding abuse, neglect, and death of humans and other vertebrates. However, development data, which are crucial for determining the age of immatures collected under forensically relevant circumstances, are limited. Given the lack of data and the recognition of population-specific growth patterns, the aim of this study was to generate data for development of a M. domestica population from Texas, USA, on decomposing lean pork at 24.0°C (i.e., approximate room temperature in Texas) and 37.0°C (i.e., approximate human body temperature). As expected, fly development significantly differed between temperatures with development at the higher temperature taking significantly less time (development from egg to adult emergence occurred c. 48.5% faster at 37.0°C than at 24.0°C). The value of this dataset is demonstrated through an applied comparison with previously published data for the house fly. Differences in development times across life stages for the studies are evident, with shorter time of colonization estimations using the data published by Wang et al. (2018), especially in later life stages. These data represent the first development dataset for the house fly on decomposing flesh in North America. Furthermore, the comparison with the previously published dataset demonstrate data from this study are of value for future forensic investigations in Texas or possibly other parts of the United States where this species is encountered, as they can be used to determine time of colonization.

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.

Can the Necrophagous Blow Fly Calliphora vicina (Diptera: Calliphoridae) Be Reared on Plant-Based Meal?

The use of the blow fly Calliphora vicina as a potential pollination species to augment the current reliance on honeybees (Apis mellifera) in Australian horticulture requires knowledge of how best to mass-rear this fly species. Calliphora vicina lays eggs onto carrion soon after death, and the resultant larvae that hatch are necrophagous and feed on the decomposing tissues of the dead animal. Newly hatched larvae of this fly were provided with plant-based meals (soya bean and canola) and compared with larvae provided with livestock-derived meatmeal to determine if plant-based meal could be used to mass-rear this blow fly species. Both soya bean and canola meal media did not support larval survival through to adult emergence. The addition of only 10% whole egg powder to the plant-based meals enabled survival to eclosion of 39% and 13% on soya bean and canola-based media, respectively, compared with 76% on livestock-based meatmeal with 10% whole egg powder. Larvae fed a diet of livestock-based meatmeal with 10% whole dried egg powder had the fastest development to the pupal stage, the highest pupation rate, the heaviest pupae, and the highest subsequent adult eclosion. This study concluded that the use of plant-based meals as a diet for the mass-rearing of the blow fly C. vicina was not a viable option.

The utility of blow fly (Diptera: Calliphoridae) evidence from burned human remains

Burning of human remains is a common method to conceal or destroy evidence associated with homicides and illegal activities. However, data regarding blow fly colonization of burned remains are scarce, with all previously published empirical studies focusing only on non-human animals. It is critically important to obtain basic data on blow fly colonization patterns of burned human remains as such evidence may represent the only feasible method for PMI estimation in cases of burning. In this study, we thermally altered six human donors to a Crow-Glassman Scale Level 3 (CGS-3) and placed them at the Anthropology Research Facility at the University of Tennessee in Summer 2021, Spring 2022, and Summer 2022. Six unburned human donors were used as controls. Observations for insect activity began within 24 h of placement and continued twice weekly through decomposition. Age estimations were performed with immature blow flies to estimate the time of colonization (TOC), and accuracy was assessed against the time of placement for each donor. All burned donors examined in this study were colonized by blow flies. No significant difference in species composition was determined between treatments, though TOC estimations from burned donors were slightly (but significantly) less accurate than TOC estimations from unburned donors (80% vs. 83% accuracy; χ2 = 0.041, df = 1, P = 0.840). These results indicate that blow flies can successfully colonize human remains burned to CGS-3 and that accurate TOC estimations can still be generated from larval specimens. Though several limitations to this study exist (e.g., inconsistent donor BMI, lack of donor temperature data), our results underscore the utility of entomological evidence in cases of burned human remains.

A novel mathematical model and application software for estimating the age of necrophagous fly larvae

The change in larval body length of necrophagous flies during their development is a key indicator for estimating larval age. However, existing forensic entomological models have limitations in this regard. In this study, a logistic algorithm was used to establish a general model for estimating the minimum postmortem interval (PMImin) using larval body length. The new model was used to simulate the relationship between larval body length and developmental time of eight species of necrophagous flies. The model parameters of body length variation with developmental time of the different species were calculated. Computer software was developed based on the established logistic model. The advantage of the new model is that each parameter has a biological meaning and can be used to estimate the age of larvae at any temperature and any larval body length. Cross-validation of the model showed that the overall mean accuracy of the fitted growth curves for the eight necrophagous fly larvae was 82.7%, the mean accuracy of age extrapolations for seven necrophagous fly species ranged from 76.8% to 92.9%, while the accuracy of age extrapolations for only one species was lower (i.e., 63.3%). This study provides a new method to estimate the PMImin based on larval body length, and the developed computer software will facilitate its application in forensic entomology.

Age determination of Chrysomya megacephala (Diptera: Calliphoridae) using lifespan patterns, gene expression, and pteridine concentration under constant and variable temperatures

Chrysomya megacephala (Fabricius, 1794) (Diptera: Calliphoridae), is a blowfly species widely studied in medical, veterinary, and entomological research. Our study examined the impact of constant (15, 20, 25, 30, and 35 °C) and variable (ranging from 21.0 to 25.4 °C, with an average of 23.31 °C) temperatures on the development and larval body length of C. megacephala. Additionally, we analyzed the age of the adult C. megacephala through pteridine content and related metabolic genes analysis. Our findings revealed three distinct growth patterns: isomorphen diagram, isomegalen diagram, and thermal accumulated models. At constant temperatures of 15, 20, 25, 30, and 35 °C, egg-hatching times were 44.5 ± 8.9, 26.7 ± 4.6, 12.6 ± 1.1, 11.0 ± 1.0, and 9.9 ± 1.9 h, respectively, while it was 15.3 ± 5.9 h at variable temperatures. The total development times from oviposition to adult eclosion in C. megacephala required 858.1 ± 69.2, 362.3 ± 5.9, 289.6 ± 17.8, 207.3 ± 9.3, and 184.7 ± 12.1 h at constant temperatures of 15, 20, 25, 30, and 35 °C, respectively. This duration was extended to 282.0 ± 64.1 h under variable temperatures. However, no significant differences were found in hatching times and the total developmental durations between 25 °C and variable temperatures. A developmental threshold temperature (D0) of 9.90 ± 0.77 °C and a thermal summation constant (K) of 4244.0 ± 347.0° hours were ascertained. Pteridine content patterns varied significantly across constant temperatures, but not between 25 °C and variable temperatures. Sex and temperature were identified as the primary factors influencing pteridine levels in the head of C. megacephala. Gene expression associated with pteridine metabolism decreased following adult eclosion, matching with increased pteridine concentration. Further investigations are needed to explore the use of pteridine cofactors for age-grading adult necrophagous flies. These findings provide valuable insights into the lifespan of C. megacephala, thereby offering valuable groundwork for forthcoming investigations and PMImin determination.

Assessment of consistency of minimum post-mortem intervals estimated by thermal summation-based methods in medico-legal cases associated with blowflies

BACKGROUND

This study is based on blow fly samples collected from 8 medico-legal cases in Tamil Nadu, India. The fly life stages were identified and the consistency of minimum post-mortem intervals (PMImin) estimated by different thermal summation-based methods was assessed.

METHODS

PMImin of 8 medico-legal cases was estimated using six different thermal summation constants and lower developmental temperatures that are based on C. megacephala and C. rufifacies developmental data. Limits of agreement (LoA), intra class correlation coefficient (ICC) between PMImin values and margin of error of mean of difference between PMImin values were calculated.

RESULTS

Intra-class correlation between the PMImin values estimated using different thermal summation constants based on C. megacephala ranged between 0.89 and 0.98 and coefficient of determination ranged between 0.93 and 0.98. Intra-class correlation between the PMImin values estimated using different thermal summation constants based on C. rufifacies ranged between 0.91 and 0.99 and coefficient of determination ranged between 0.95 and 0.99. The mean difference of PMImin values estimated using different thermal summation methods based on C. megacephala ranged between 1.8 hr and 6.6hr and margin of error ranged between 2.51 and 6.93hr. The mean difference of PMImin values estimated using different thermal summation methods based on C. rufifacies ranged between 3.33 and 31.33hr and margin of error ranged between 4.66 and 32hr.

CONCLUSION

Consistency of PMImin values estimated by different thermal summation methods was good to excellent. Thermal summation constants useful in estimation of PMImin with lowest mean difference and margin of error were described.

Effects of Tissue Type and Temperature on Selected Life-History Traits of the Flesh Fly, Sarcophaga crassipalpis (Macquart, 1839) (Diptera: Sarcophagidae)

The flesh fly, Sarcophaga crassipalpis Macquart 1839 (Diptera: Sarcophagidae), colonizes estimation of the minimum post-mortem interval (min-PMI). This study examined the effects of different types of tissues and temperature on the development of S. crassipalpis. To the best of our knowledge, the present study is the first to investigate the effects of life-history information of S. crassipalpis. Larvae were reared on three tissue types, chicken heart, bovine minced meat, and bovine tongue, at five temperatures, 15, 20, 25, 30, and 32°C. Pupal and larval development time, adult weight, and pupal and larval survival differed significantly for tissue type and temperature. Temperature had a significant effect on pupal weight but tissue type did not significantly affect pupal weight. The duration of the larval and pupal stages (except of chicken heart, 30°C) decreased with increasing temperature, except for 32°C, in all tissue types. Larval survival was lowest at 32°C in bovine minced meat, bovine tongue, and chicken heart, and at 32°C, all pupae failed to reach the adult stage in minced meat. The results of this study highlight the necessity of considering larval diet and temperature in forensic investigations.

Not by the Book: Observations of Delayed Oviposition and Re-Colonization of Human Remains by Blow Flies

Postmortem interval estimations can be complicated by the inter-individual variation present in human decomposition. Forensic entomologists may especially face challenges interpreting arthropod evidence in scenarios that are not "by the book", or that vary in unexpected ways. Therefore, it is important to report instances where blow fly colonization does not align with expected soft tissue decomposition as blow fly larvae are often used to produce a time of colonization (TOC) estimation to infer a minimum PMI. We followed the decomposition and blow fly activity of three human donors at the Anthropology Research Facility (University of Tennessee). Delayed oviposition occurred on one donor 115 d post-placement, whereas two donors experienced blow fly re-colonization after cessation of the consumption phase, one 22 d and one more than 200 d after blow fly larvae were last observed. A null hypothesis model tested whether the entomological TOC and anthropological total body score (TBS) estimations encompassed the time of placement (TOP) for each donor. While the null hypothesis was rejected for all TOC estimations, it could not be rejected for the TBS estimations. We discuss how the non-linear nature of human decomposition can pose challenges to interpreting blow fly evidence and suggest that forensic entomology practitioners should recognize these limitations in both research endeavors and applied casework.

Coexistence and intraguild competition of Chrysomya albiceps and Lucilia sericata larvae: case reports and experimental studies applied to forensic entomology

The larval development of Chrysomya albiceps and Lucilia sericata is a well-known and valuable tool for estimating the postmortem interval (PMI). The third instar larvae of Ch. albiceps are facultative predators of the larvae of other necrophagous dipterans, and this behaviour is undoubtedly an important factor to consider. Both species are found together during human autopsies in Spain and other parts of Europe, where they cohabit, so a precise knowledge of their larval coexistence data is essential. The aim of this study is to investigate their coexistence and the intraguild predation of Ch. albiceps on L. sericata under experimental conditions and in real case reports. To analyse intra- and interspecific competition, four densities were used under controlled abiotic conditions [25ºC, 60-70% RH and 12:12 (D:N)]. The experimental data were compared with data corresponding to their coexistence in natural conditions, so annual activity and forensic case reports for both species were studied. The results indicate that the mortality of immature specimens in both species, the preimaginal developmental time, and adult size were affected by competition. In natural conditions, adult coexistence during the spring-summer period was confirmed. The simultaneity of the two species colonising human corpses is frequent in the studied area, with Ch. albiceps being the dominant species, and L. sericata the relevant species for estimating the minimum postmortem interval.

Life Cycle of Chrysomya rufifacies (Diptera: Calliphoridae) Under Semi-Controlled Laboratory Conditions

Adult Calliphoridae flies, as well as their immature stages collected from carcasses, have been used as evidence in forensic investigations to estimate the postmortem interval (PMI), particularly those of the genus Chrysomya as it is one of the first genera to colonize a corpse. Chrysomya rufifacies (Macquart 1842), due to its appearance in cadaveric remains, plays a fundamental role in the study of forensic entomology. For this reason, we determined the biological cycle of C. rufifacies under semicontrolled laboratory conditions: uncontrolled average fluctuating temperature of 29. 76 ± 3. 22°C, uncontrolled average fluctuating humidity of 48. 91 ± 11.13%, and a controlled photoperiod of 12/12 (L/O). We established that the total development time from oviposition to adult emergence of C. rufifacies was 6. 5 d. The eggs took 12 h to hatch after oviposition. The complete larval stage took 60 h (instar 1 = 12 h, instar 2 = 12 h, instar 3 = 24 h, instar 3 post-feeding = 12 h). The pupa had a duration of 84 h. The species needed a total of 4642.8(±4.59) accumulated degree-hours (ADH) to complete its biological cycle.

Research Progress on Developmental Biology of Sarcosaprophagous Insects

Forensic entomology provides a feasible way to estimate postmortem interval (PMI), of which the growth and development of sarcosaprophagous insects is the most widely used indicator in forensic practice. Over the years, forensic entomologists have carried out a large number of studies on the development biology of sarcosaprophagous insects. This paper illustrates the main factors that affect the development of sarcosaprophagous insects, including temperature, humidity, light, food types and poisons. The development indicators of sarcosaprophagous insects were reviewed from the perspectives of morphology, differential gene expression and biochemical characteristics. It is emphasized that future research of development biology on sarcosaprophagous insects should fully absorb and integrate the methods of artificial intelligence and omics, and the research object also needs further expansion in order to establish a more objective and more accurate PMI estimation method.

Sexual Dimorphism in Growth Rate and Gene Expression Throughout Immature Development in Wild Type Chrysomya rufifacies (Diptera: Calliphoridae) Macquart

Reliability of forensic entomology analyses to produce relevant information to a given case requires an understanding of the underlying arthropod population(s) of interest and the factors contributing to variability. Common traits for analyses are affected by a variety of genetic and environmental factors. One trait of interest in forensic investigations has been species-specific temperature-dependent growth rates. Recent work indicates sexual dimorphism may be important in the analysis of such traits and related genetic markers of age. However, studying sexual dimorphic patterns of gene expression throughout immature development in wild-type insects can be difficult due to a lack of genetic tools, and the limits of most sex-determination mechanisms. Chrysomya rufifacies, however, is a particularly tractable system to address these issues as it has a monogenic sex determination system, meaning females have only a single-sex of offspring throughout their life. Using modified breeding procedures (to ensure single-female egg clutches) and transcriptomics, we investigated sexual dimorphism in development rate and gene expression. Females develop slower than males (9 h difference from egg to eclosion respectively) even at 30°C, with an average egg-to-eclosion time of 225 h for males and 234 h for females. Given that many key genes rely on sex-specific splicing for the development and maintenance of sexually dimorphic traits, we used a transcriptomic approach to identify different expression of gene splice variants. We find that 98.4% of assembled nodes exhibited sex-specific, stage-specific, to sex-by-stage specific patterns of expression. However, the greatest signal in the expression data is differentiation by developmental stage, indicating that sexual dimorphism in gene expression during development may not be investigatively important and that markers of age may be relatively independent of sex. Subtle differences in these gene expression patterns can be detected as early as 4 h post-oviposition, and 12 of these nodes demonstrate homology with key Drosophila sex determination genes, providing clues regarding the distinct sex determination mechanism of C. rufifacies. Finally, we validated the transcriptome analyses through qPCR and have identified five genes that are developmentally informative within and between sexes.

Effect of Type of Tissue on the Development of Chrysomya rufifacies (Diptera: Calliphoridae) in Sri Lanka

Chrysomya rufifacies (Macquart), the hairy maggot blow fly, is of great importance for the field of forensic entomology due to its habit as an early colonizer of decomposing vertebrate remains and myiasis producer. Development studies on this species have been conducted in scattered regions of the world, using types of tissue from several species of animals as a rearing medium. Despite the commonality of C. rufifacies in Sri Lanka, developmental studies have never been performed in this region. As well, the effects of diet on development have not been tested. In the current study, C. rufifacies immatures were reared on skeletal muscle, liver, and heart from domestic swine, with flies from colonies maintained at 25 and 28°C. The minimum time needed to complete each stage at 25°C on liver (224.14 h) was fastest followed by skeletal muscle (249.33 h) and heart (251.64 h) respectively, whereas at 28°C, fly development was quickest on heart muscle (178.27 h) followed by liver (178.50 h) and skeletal muscle (186.17 h) respectively. A significant difference in total development time was determined for temperature, while the rearing medium was not significant. Temperature also showed a significant effect on the length and the width of the larvae, while the type of tissue statistically impacted only the width.

Dietary Effects on the Development of Calliphora dubia and Chrysomya rufifacies (Diptera: Calliphoridae): Implications for Postmortem Interval

Forensic entomology relies on insect development data generated within a laboratory setting in the estimation of minimum postmortem interval (mPMI). The methodologies used to produce these data vary considerably within the field and there is no accepted standard approach to laboratory rearing of forensically relevant species. A wide range of rearing media are used across published studies, including different species of animal and types of tissue (e.g., muscle and liver). Differing methodologies, particularly rearing diet, can introduce considerable variation into the baseline data upon which forensic estimates of the mPMI are calculated. Consequently, research establishing a widely available, standard and/or optimal, rearing medium for blow fly development for forensic application is desirable. This study examined dietary effects on the development of two forensically relevant blow fly species: Calliphora dubia Macquart, 1855, and Chrysomya rufifacies Macquart 1842 (Diptera: Calliphoridae). Larvae of both species were reared on pork liver, pork mince, pork loin, beef liver, beef mince, and guinea pig carcass under two constant temperature regimes (24 ± 1°C and 30 ± 1°C; 70 ± 10% humidity; 12-h/12-h photoperiod) to assess the influence of temperature on developmental response to diet. Fundamental developmental data pertaining to both species are reported. Developmental response to diet was species-specific and influenced by temperature with indication that the optimal temperature for C. dubia development is below 30°C. Pork mince was the most appropriate dietary standard of the rearing media investigated for the formulation of forensic development data for both species investigated.

Effects of Photoperiod on the Development of Forensically Important Blow Fly Chrysomya rufifacies (Diptera: Calliphoridae)

Estimation of the time of colonization (TOC) is often based on laboratory studies that document arthropod development. Precise data for forensically important species, such as blow flies (Diptera: Calliphoridae), are essential for accuracy in the estimate of TOC. Calliphorid development is a quantitative trait and thus depends on a host of variables. In calliphorids, studies showed photoperiod can play a role in development. However, there has been little research to date on the effects of photoperiod, and available data indicate the impact is species-specific. In this study, the effects of photoperiod on the development of Chrysomya rufifacies (Macquart), were examined. Chrysomya rufifacies is a fly of great medical and legal importance and is often encountered on vertebrate remains in temperate and tropic regions throughout the world, including North and Central America, Asia, and Australia. Larvae were reared under light regimes of 12, 16, and 24 h of light at 28.5 ± 0.0°C, 86.2 ± 0.3 RH. Minimum development time for each stage did not differ significantly for the applied photoperiods, nor were there significant differences in total minimum postembryonic development time. Photoperiod did not significantly affect larval size or growth rate. The data suggest that light durations investigated in this study do not influence the development of C. rufifacies. This indicates that photoperiod may not be a concern for forensic entomologists in Texas, United States, or other areas with similar conditions when estimating the TOC for this species. Validation efforts are encouraged to verify this conclusion.

Impact of diet moisture on the development of the forensically important blow fly Cochliomyia macellaria (Fabricius) (Diptera: Calliphoridae)

The secondary screwworm, Cochliomyia macellaria (Fabricius) (Diptera: Calliphoridae), is a carrion-breeding species of veterinary, medical, and forensic importance. It is very abundant in the Nearctic and Neotropical regions and is one of the most common colonizers of vertebrate remains in the southern United States. Therefore, it is of great evidential value in estimating the minimum time of colonization (TOC) of remains related to forensic investigations. So far, studies have investigated the effects of several biotic and abiotic factors on C. macellaria. However, no data on the specific impact of food source moisture on the larval development of this species are known to have been published. In this study, the effects of diet moisture on larval development time, larval length, and weight over time, as well as adult emergence and weight were investigated. C. macellaria was reared on diets prepared from freeze-dried bovine liver with varying moisture content (0.0, 33.0, 50.0, or 70.8%) at 25.6 °C, 77% RH, and 14:10 L:D. Frozen-thawed liver was used as a control. Water content was found to significantly impact immature development time and corresponding life-history traits, both within and among developmental stages of C. macellaria. This result indicates moisture content of the carrion source should be considered when estimating time of colonization and identification of immature stage of flies in forensic investigations. Furthermore, as diet moisture content significantly affected the dry mass of emerging adults, the mass of adults collected at a crime scene could provide useful information as it could be an indicator of the condition the remains were in during time of colonization, including the moisture content of the tissue.

Field Validation of a Development Data Set for Cochliomyia macellaria (Diptera: Calliphoridae): Estimating Insect Age Based on Development Stage

Insect age estimates can be useful for estimating the postmortem interval when certain assumptions are met. Such estimates are based on species-specific development data that are temperature-dependent and variable, and therefore prone to different degrees of error depending on the combination of data sets, calculations, and assumptions applied in a specific instance. Because of this potential error, validating the methods employed is necessary for determining accuracy and precision of a given technique. For forensic entomology, validation of development data sets is one approach for identifying the uncertainty associated with insect age estimates. Cochliomyia macellaria (Fabricius) is a primary colonizer of remains across the United States and is commonly encountered in forensic investigations. A development study for this species was produced for a central Texas, U.S. population; the variation associated with this data set and the pre-appearance interval were previously explored in an ecological model. The objectives of this study were to determine the accuracy of the development data and the validity of the ecological model when applied to immatures of known age developing under field conditions. Results indicate this data set is an accurate predictor of insect age when using development stage, supporting the validity of the ecological model in central Texas. Age predictions made with all stages present in a sample were more accurate than predictions made with the most developed stage in a sample, and estimates of age when using the prepupal stage were overestimated regardless of prediction method, though thermal requirements for total development were similar.

Intrapuparial Development of Hemilucilia semidiaphana (Diptera: Calliphoridae) and Its Use in Forensic Entomology

In forensic entomology, the minimum postmortem interval (PMImin) estimative is usually based on the oldest immature recovered from a local of death. The time spent by fly immatures in the intrapuparial period comprises more than 50% of their complete life cycles. An accurate estimate of the duration of this period will improve PMImin estimates. The blow fly Hemilucilia semidiaphana (Rondani 1850) was found in six criminal cases in the city of Curitiba. Even though there is data on the morphology of the larval instars and developmental rate of H. semidiaphana, the intrapuparial period has not been investigated. Here, we provide a detailed description of the intrapuparial morphological changes of H. semidiaphana, which might be useful to estimate minimum PMI. Samples of H. semidiaphana in the intrapuparial period were obtained from immatures reared on an artificial diet in incubators adjusted to 25°C or 20°C temperature regimes. Blow fly puparia of H. semidiaphana were fixed at intervals of 3 and 6 h until emergence of the adult. The external morphological traits of sampled immatures were analyzed using light microscopy. Our analysis of the intrapuparial period of H. semidiaphana provided 21 traits from which nine were age informative. These nine characteristics divide the developmental time (144 h at 25°C and 192 h at 20°C) into smaller sections. The developmental data provided, together with the time line allows a practical way to make interspecific comparisons as well as to estimate the age of H. semidiaphana based on the intrapuparial development.

Effect of Temperature and Tissue Type on the Development of the Forensic Fly Chrysomya megacephala (Diptera: Calliphoridae)

Chrysomya megacephala Fabricius is one of the most common myiasis-causing and carrion-feeding fly species in the tropics. This species has a worldwide distribution due to globalization and therefore is of critical importance to the public health sector and forensic investigations. Development studies carried worldwide show that Ch. megacephala reared at similar temperatures may require different amounts of time to complete their cycle of growth. The present study determined for the first time the life-history information of this species in Sri Lanka. Chrysomya megacephala colonies were reared on three different food sources (bovine muscle, swine muscle, and swine liver) considering the most common forensic entomology rearing mediums and the capability of Ch. megacephala to cause myiasis in cattle. Furthermore, colonies were reared at four temperature regimes representing several specific development conditions of this blowfly: 1) 20°C representing the estimation of the lower developmental threshold for this species in Sri Lanka; 2) 25 and 27°C representing typical room/environmental temperatures in Sri Lanka; and 3) 38°C as this is the typical living animal temperature, representing myiasis conditions. Results show that temperature significantly affected larval length and width over time; however, tissue type was not a significant factor. The fastest development was recorded at 38°C for immature feeding on bovine muscle (162.15 h), followed by those fed swine liver (184.15 h) and swine muscle (208.00 h). The calculated minimum temperature threshold for Ch. megacephala was 13°C. Data generated will be crucial for future forensic investigations involving living or deceased individuals colonized by this species.

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.

Development of Chrysomya rufifacies (Diptera: Calliphoridae) at Constant Temperatures Within its Colony Range in Yangtze River Delta Region of China

The age of insects found on corpses is often used to estimate the minimum postmortem interval by forensic entomologists. Insect development is affected by biotic and abiotic factors, and temperature is the most important environmental factor that determines the length of insect development. Chrysomya rufifacies (Macquart) (Diptera: Calliphoridae) is a globally distributed fly that is commonly found on corpses, and this study investigated the development of C. rufifacies from China at various constant temperatures. At 16, 19, 22, 25, 28, 31, and 34°C, the developmental time from egg to adult was 870.17 ± 11.50, 566.20 ± 8.79, 406.38 ± 10.98, 291.14 ± 4.71, 232.59 ± 5.96, 192.47 ± 3.45, and 160.48 ± 7.15 h, respectively. We established three developmental models for C. rufifacies to estimate the age of the developing insect: the isomorphen diagram model, the isomegalen diagram model and the thermal summation model. Regression analysis was conducted to obtain the relationship between body length and development time of the larvae from hatching to wandering. The developmental threshold temperatures of the egg, 1st instar, 2nd instar, 3rd instar, and wandering larvae, and intra-puparial stages were 12.28 ± 0.30, 11.74 ± 0.95, 12.70 ± 0.55, 11.68 ± 0.96, 10.53 ± 1.53, and 12.51 ± 0.41°C, respectively. The developmental threshold temperature, and the thermal summation constant during the entire developmental period were 3759.95 ± 170.80 degree hours and 11.96 ± 0.38°C, respectively. This study provides an improved dataset to estimate the postmortem interval of corpses using C. rufifacies.

The Effects of Diets and Long-term Laboratory Rearing on Reproduction, Behavior, and Morphology of Lucilia cuprina (Diptera: Calliphoridae)

The Australian sheep blow fly, Lucilia cuprina (Wiedemann), is commonly reared in the laboratory for many sequential generations on simple, fixed diets, so it can be used in veterinary, medical, and forensic studies. To investigate the effect of diet and long-term laboratory rearing on L. cuprina, flies were fed with two different diets (sugar and milk-sugar) over a year and F1, F6, and F11 generations were used for comparisons based on the number of eggs, attraction to wool and liver, and wing size. The results showed that the number of eggs of gravid flies, and the attractiveness of wool and liver did not differ significantly between diets and generations, but gravid flies were more attracted to wool and liver than non-gravid flies (P < 0.05). Moreover, in the F1 generation, thorax length and wing aspect ratio were significantly longer than in the F6 and F11 generations (P < 0.05), and the wing length was significantly longer than in the F11 generation (P < 0.05). It was concluded that neither diet nor long-term laboratory rearing affect potential fecundity or the behavioral responses of L. cuprina, but the gravidity of flies affects their behavioral response, and long-term laboratory rearing significantly affects fly morphology, apparently explaining a loss in flight performance.

Effect of Temperature and Tissue Type on the Development of Myiasis Causing Fly; Chrysomya bezziana (Diptera: Calliphoridae)

Chrysomya bezziana Villeneuve is the major human myiasis producer in tropical countries, including Sri Lanka. Although of great medical and veterinary importance, only a single study has been published on the development of C. bezziana. This limitation is due in part to the difficulty of maintaining this species in a colony outside of using a living host. In this study, a novel technique that overcomes this limitation is presented along with development data for C. bezziana fed on three different meat types: swine muscle, swine liver, and bovine muscle at two temperature regimes: 35 and 37°C. The optimum development of C. bezziana was recorded at 35°C in bovine muscle (262.20 h) followed by swine muscle (286.00 h) and swine liver (307.00 h). Data from the current study indicate tissue type significantly impacts change in length and width of larvae over time, whereas the two temperatures examined had no significant effect.

Chronology of the Intrapuparial Development of the Blowfly Chrysomya albiceps (Diptera: Calliphoridae): Application in Forensic Entomology

Insects display different patterns of development, and blow flies have one of the most specialized patterns of intrapuparial development of all. In forensic entomology, pupae can be used as a tool to estimate the minimum postmortem time interval (minPMI). We analyzed the intrapuparial development of Chrysomya albiceps (Diptera: Caloricidade), whose larvae had been fed pig lungs and reared in a climate-controlled room at 28°C day/26°C night, 70 ± 10% RH, and 12 h of photophase and monitored daily. After the third-instar larvae abandoned their diet, the process of pupariation and pupation was monitored. At pre-established times, five pupae were collected, euthanized, and fixed in 5% formaldehyde, inside polypropylene test tubes with caps. Since they were the first, they were classified as 0 h pupae. Twelve collections occurred until the emergence of the adults, at 0, 2, 4, 6, 8, 10, 24, 30, 48, 54, 72, 78, 96, and 99 h (n = 84). The fixed pupae were dissected under the microscope, with the aid of anatomical tweezers and hypodermic needles, and photographed. The stages of metamorphosis and the morphological alterations occurring during the process were identified, described, and recorded before and after pupation. These phases were: pupation, larval pupal apolysis, cryptocephalic, phanerocephalic, pharate adult, emergence, and adult. The cryptophalic phase occurred between 4 and 6 h after pupation; the phanerocephalic phase between 6 and 10 h after; the pharate adult phase between 24 and 96 h after; and the imago/emergence phase 99 h after pupation.

Temperature and Tissue Type Impact Development of Lucilia cuprina (Diptera: Calliphoridae) in Sri Lanka

Lucilia cuprina (Wiedemann; Diptera: Calliphoridae) is a facultative ecto-parasitic fly, distributed throughout the temperate and subtropical regions of the world. This blow fly species is of medical, veterinary, and forensic importance due to it being used in maggot debridement therapy (MDT), a causative agent of myiasis, and a decomposer of vertebrate carrion. The current study examined the combined effects of temperature and tissue type on the development of L. cuprina. Specimens were reared on three tissue types; swine muscle, swine liver, and bovine muscle at 20°C, 25°C, 27°C, and 38°C. The optimum condition for L. cuprina development was for immatures reared on bovine muscle (287.4 h) followed by those reared on swine muscle (288.0 h) and swine liver (288.4 h) at 27°C. The minimum temperature threshold of L. cuprina was deduced to be 14°C. No significant differences in larval width and length over time were determined for the tissue type.

Hyperspectral measurements of immature Lucilia sericata (Meigen) (Diptera: Calliphoridae) raised on different food substrates

Immature Lucilia sericata (Meigen) raised on beef liver, beef heart, pork liver and pork heart at a mean temperature of 20.6°C took a minimum of 20 days to complete development. Minimum development time differences within stages were observed between the meat types (pork/beef), but not the organ types (liver/heart). Daily hyperspectral measurements were conducted and a functional regression was completed to examine the main effects of meat and organ type on daily spectral measurements. The model examined post feeding larval spectral measurements of insects raised on beef liver alone, the effect of those raised on pork compared with those raised on beef, the effect of those raised on heart compared with those raised on liver and the interactional effect of those raised on pork heart compared with those raised on beef liver. The analyses indicated that the spectral measurements of post feeding L. sericata raised on pork and beef organs (liver and heart) are affected by the meat and organ type.

Size at emergence improves accuracy of age estimates in forensically-useful beetle Creophilus maxillosus L. (Staphylinidae)

Insects colonizing human or animal cadavers may be used to estimate post-mortem interval (PMI) usually by aging larvae or pupae sampled on a crime scene. The accuracy of insect age estimates in a forensic context is reduced by large intraspecific variation in insect development time. Here we test the concept that insect size at emergence may be used to predict insect physiological age and accordingly to improve the accuracy of age estimates in forensic entomology. Using results of laboratory study on development of forensically-useful beetle Creophilus maxillosus (Linnaeus, 1758) (Staphylinidae) we demonstrate that its physiological age at emergence [i.e. thermal summation value (K) needed for emergence] fall with an increase of beetle size. In the validation study it was found that K estimated based on the adult insect size was significantly closer to the true K as compared to K from the general thermal summation model. Using beetle length at emergence as a predictor variable and male or female specific model regressing K against beetle length gave the most accurate predictions of age. These results demonstrate that size of C. maxillosus at emergence improves accuracy of age estimates in a forensic context.

Development of Chrysomya megacephala at constant temperatures within its colony range in Yangtze River Delta region of China

Chrysomya megacephala (Fabricius, 1794) is the most abundant and predominant species which arrives and colonizes a cadaver first in most parts of China. Therefore, its growth and development patterns have great implications in the estimation of the minimum postmortem interval (PMImin). In this study, C. megacephala was collected from the Yangtze River Delta region and reared at seven constant temperatures ranging from 16 °C to 34 °C. The developmental duration and accumulated degree hours, larval body length and morphological changes of C. megacephala were examined. Furthermore, we constructed three developmental models, isomorphen diagram, isomegalen diagram and thermal summation model, which can be used for estimating PMImin. The developmental durations of C. megacephala at 16 °C, 19 °C, 22 °C, 25 °C, 28 °C, 31 °C and 34 °C are (794.8 ± 14.7), (533.2 ± 10.1), (377.8 ± 16.8), (280.8 ± 15.1), (218.9 ± 8.5), (190.8 ± 10.1) and (171.8 ± 6.8) h, respectively. The developmental threshold temperature D 0 is (11.41 ± 0.32) °C, and the thermal summation constant K is (3 418.7 ± 137.0) degree hours. Regression analysis was conducted to obtain equations of the variation in larval body length with time after hatching, and variation in time after hatching with body length. Moreover, our study divides the intra-puparial morphological changes of C. megacephala into 11 sub-stages, and provides the time range experienced by each sub-stage. The results of this study provide fundamental development data for the use of C. megacephala in PMImin estimations.

Mass mortality events and the role of necrophagous invertebrates

Scale is important in understanding and applying concepts in ecology. Historically, the mechanisms regulating necrophagous arthropod community structure have been well explored on a single vertebrate carcass. However, practically nothing is known of whether such findings can be extrapolated to cases where large numbers of carcasses have been introduced into an ecosystem at a single time point. With the increasing incidences of mass mortality events (MMEs), understanding how scale effects community assembly of necrophagous insects and the resulting bottom-up or top-down effects on the impacted ecosystem are of utmost importance. Unfortunately, MMEs are unpredictable, making their study nearly impossible within a robust experimental framework. The objectives of this paper are to provide a brief overview of what is known with regards to ecological responses to carrion, opine on the ramifications of MMEs on local communities, and provide a brief overview of knowledge gaps, avenues for future research, and a potential study systems for rigorous MME experiments.

Quantifying pteridines in the heads of blow flies (Diptera: Calliphoridae): Application for forensic entomology

In forensic cases involving entomological evidence, establishing the postcolonization interval (post-CI) is a critical component of the investigation. Traditional methods of estimating the post-CI rely on estimating the age of immature blow flies (Diptera: Calliphoridae) collected from remains. However, in cases of delayed discovery (e.g., when remains are located indoors), these insects may have completed their development and be present in the environment as adults. Adult fly collections are often ignored in cases of advanced decomposition because of a presumed little relevance to the investigation; herein we present information on how these insects can be of value. In this study we applied an age-grading technique to estimate the age of adults of Chrysomya megacephala (Fabricius), Cochliomyia macellaria (Fabricius), and Phormia regina (Meigen), based on the temperature-dependent accumulation of pteridines in the compound eyes, when reared at temperatures ranging from 5 to 35°C. Age could be estimated for all species*sex*rearing temperature combinations (mean r²±SE: 0.90±0.01) for all but P. regina reared at 5.4°C. These models can be used to increase the precision of post-CI estimates for remains found indoors, and the high r² values of 22 of the 24 regression equations indicates that this is a valid method for estimating the age of adult blow flies at temperatures ≥15°C.

Development of the Forensically Important Beetle Creophilus maxillosus (Coleoptera: Staphylinidae) at Constant Temperatures

Creophilus maxillosus (L., 1758) is a common and widely distributed beetle species found on corpses, and its development duration is far longer than species belonging to the genus Calliphoridae and Sarcophagidae. Therefore, C. maxillosus can be used as a supplementary indicator to estimate minimum postmortem interval (PMImin), and could greatly extend the range of PMImin when the primary colonizers are no longer associated with the corpse or have emerged from pupae. Better descriptions of C. maxillosus development are needed to apply this species for forensic investigations. In this study, the development of C. maxillosus at seven constant temperatures ranging from 17.5-32.5 °C was studied. Through regression analyses, the simulation equations of larval body length variation with time after hatching were obtained. Isomegalen diagrams of the changes of larval body length over time at specific temperatures, and the isomorphen diagrams on the duration of different developmental milestones at specific temperatures were generated. In addition, thermal summation models of different developmental stages and the overall development process of C. maxillosus were generated through regression analysis, by estimating the development threshold temperatures (D0) and the thermal summation constants (K). These results provide important tools for forensic investigations to generate a long-range of PMImin estimation based on the development of C. maxillosus.

Development of the Oriental Latrine Fly, Chrysomya megacephala (Diptera: Calliphoridae), at Five Constant Temperatures

Chrysomya megacephala (Fabricius) is a forensically important fly that is found throughout the tropics and subtropics. We calculated the accumulated development time and transition points for each life stage from eclosion to adult emergence at five constant temperatures: 15, 20, 25, 30, and 35 °C. For each transition, the 10th, 50th, and 90th percentiles were calculated with a logistic linear model. The mean transition times and % survivorship were determined directly from the raw laboratory data. Development times of C. megacephala were compared with that of two other closely related species, Chrysomya rufifacies (Macquart) and Phormia regina (Meigen). Ambient and larval mass temperatures were collected from field studies conducted from 2001-2004. Field study data indicated that adult fly activity was reduced at lower ambient temperatures, but once a larval mass was established, heat generation occurred. These development times and durations can be used for estimation of a postmortem interval (PMI).

Fluorescence Imaging of Posterior Spiracles from Second and Third Instars of Forensically Important Chrysomya rufifacies (Diptera: Calliphoridae). J Forensic Sci 2016;61:1578-1587. [PMID: 27706817 DOI: 10.1111/1556-4029.13189]

Entomological protocols for aging blowfly (Diptera: Calliphoridae) larvae to estimate the time of colonization (TOC) are commonly used to assist in death investigations. While the methodologies for analyzing fly larvae differ, most rely on light microscopy, genetic analysis, or, more rarely, electron microscopy. This pilot study sought to improve resolution of larval stage in the forensically important blowfly Chrysomya rufifacies using high-content fluorescence microscopy and biochemical measures of developmental marker proteins. We established fixation and mounting protocols, defined a set of measurable morphometric criteria and captured developmental transitions of 2nd instar to 3rd instar using both fluorescence microscopy and anti-ecdysone receptor Western blot analysis. The data show that these instars can be distinguished on the basis of robust, nonbleaching, autofluorescence of larval posterior spiracles. High-content imaging techniques using confocal microscopy, combined with morphometric and biochemical techniques, may therefore aid forensic entomologists in estimating TOC.

Effects of temperature and diet on black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae), development

The black soldier fly, Hermetia illucens, is recognised for its use in a forensic context as a means for estimating the time of colonisation and potentially postmortem interval of decomposing remains. However, little data exist on this species outside of its use in waste management. This study offers a preliminary assessment of the development, and subsequent validation, of H. illucens. Larvae of H. illucens were reared at three temperatures (24.9°C, 27.6°C and 32.2°C) at 55% RH on beef loin muscle, pork loin muscle and a grain-based diet (control). Each of the temperatures and diets were found to significantly (P<0.05) affect all stages of immature growth except for pupation time. Overall, those reared on the pork diet required on average ≈23.1% and ≈139.7% more degree hours to complete larval development than those reared on the beef and grain-based diets, respectively. Larvae reared at 27.6°C and 32.2°C required on average ≈8.7% more degree hours to complete development and had a final larval weight ≈30% greater than larvae reared at 24.9°C. The validity of the laboratory larval length and weight data sets was assessed via estimating the age of field-reared larvae. Grain-diet data lacked accuracy when used to estimate larval age in comparison to estimates made with beef and pork-diet data, which were able to predict larval age for ≈55.6% and ≈88.9% of sampling points, respectively, when length and weight data were used in conjunction. Field-reared larval sizes exceeded the maximum observed under laboratory conditions in almost half of the samples, which reduced estimate accuracy. Future research should develop additional criteria for identifying development of each specific instar, which may aid in improving the accuracy and precision of larval age estimates for this species.