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

Challenges and considerations in forensic entomology: A comprehensive review

Forensic entomology is the study of insect biology as it relates to societal problems that come to the attention of the legal profession and that often must be resolved by legal proceedings. These problems come under the purview of medico-criminal entomology. Forensic entomology is the study of arthropods, especially insects, their identification, post-mortem intervals (PMI), crime scene details associated with crimes and other aspects of the courts and judicial system. Understanding the predictable succession patterns of Diptera and Coleoptera on decomposing remains is crucial for accurately determining the post-mortem interval in forensic investigations. Beetles and blowflies play a critical role in the decomposition process, with beetles often appearing later and blowflies swiftly colonizing remains, making both essential for accurately estimating the post-mortem interval and understanding decomposition dynamics. Insects, particularly flies, serve as crucial forensic tools, allowing for detecting drugs, poisons, and other substances long after traditional tissue samples degrade. Their ability to retain and reveal evidence, even in severely decomposed or altered remains, significantly enhances the accuracy of criminal investigations. Recent advancements in forensic entomology, such as integrating infrared spectroscopy, omics technologies, and molecular taxonomy, have significantly improved the precision and scope of forensic investigations. These tools, combined with thorough validation processes, enable forensic scientists to identify species, estimate post-mortem intervals, and interpret complex cases with greater accuracy and reliability. However, challenges such as environmental influences, insect behavior, body concealment, faunal succession limitations, and gaps in knowledge and resources present obstacles to accuracy and standardization. This review summarises key insect species involved in crime Investigation, PMI Intervals and their significance, Recent advances, Challenges and limitations so that entomotoxicologists can analyze challenging cases recovered after a long period this review also analyses the scope of entomotoxicology in the area of death investigations.

Age, sex, and mating status discrimination in the sand fly Lutzomyia longipalpis using near infra-red spectroscopy (NIRS)

BACKGROUND

Understanding aspects related to the physiology and capacity of vectors is essential for effectively controlling vector-borne diseases. The sand fly Lutzomyia longipalpis has great importance in medical entomology for disseminating Leishmania parasites, the causative agent of Leishmaniasis, one of the main neglected diseases listed by the World Health Organization (WHO). In this respect, it is necessary to evaluate the transmission potential of this species and the success of vector control interventions. Near-infrared spectroscopy (NIRS) has been used to estimate the age of mosquitoes in different conditions (laboratory, semi-field, and conservation), taxonomic analysis, and infection detection. However, no studies are using NIRS for sand flies.

METHODS

In this study, we developed analytic models to estimate the age of L. longipalpis adults under laboratory conditions, identify their copulation state, and evaluate their gonotrophic cycle and diet.

RESULTS

Sand flies were classified with an accuracy of 58-82% in 3 age groups and 82-92% when separating them into young (<8 days) or old (>8 days) insects. The classification between mated and non-mated sandflies was 98-100% accurate, while the percentage of hits of females that had already passed the first gonotrophic cycle was only 59%.

CONCLUSIONS

We consider the age and copula estimation results very promising, as they provide essential aspects of vector capacity assessment, which can be obtained quickly and at a lower cost with NIRS.

Analysis of the Influence of Changing and Fixed Temperatures on the Growth and Pteridine Content in the Head of Adults Sarcophaga crassipalpis (Diptera: Sarcophagidae)

Flesh flies (Diptera: Sarcophagidae) are regarded as significant in medical and veterinary entomology, and their development models can be utilized as considerable markers to ascertain the minimum postmortem interval (PMImin). In this research, we explored the growth cycle and larval body length of Sarcophaga crassipalpis Macquart 1839 (Diptera: Sarcophagidae) reared under variable temperatures ranging from 15.7 to 31.1 °C, with an average of 24.55 °C and relative humidity ranges from 31.4 to 82.8% and at six fixed temperatures of 15, 20, 25, 30, 32, and then 35 °C. Moreover, pteridine from the head was used to assess adult age grading. Our results allowed us to provide three development models: the isomorphen chart, the isomegalen chart, and the thermal summation models. The time taken for S. crassipalpis to complete its development from larviposition to adult emergence at constant temperatures of 15, 20, 25, 30, 32, and 35 °C was 1256.3 ± 124.2, 698.6 ± 15.1, 481.8 ± 35.7, 366.0 ± 13.5, and 295.8 ± 20.5 h, respectively, except 35 °C, where all pupae were unable to attain adulthood. They lasted 485.8 ± 5.4 h under variable temperatures. The minimum developmental limit (D0) temperature and the thermal summation constant (K) of S. crassipalpis were 9.31 ± 0.55 °C and 7290.0 ± 388.4 degree hours, respectively. The increase in pteridine content exhibited variations across different temperatures. There was quite a considerable distinction in the pteridine contents of male and female S. crassipalpis at 15 °C (p = 0.0075) and 25 °C (p = 0.0213). At 32 °C and variable temperatures, the pteridine content between female and male S. crassipalpis was not statistically divergent. However, temperature and gender remain the main factors influencing the pteridine content in the head of S. crassipalpis. We aim to provide detailed developmental data on S. crassipalpis that can be used as a valuable resource for future research and PMI estimation.

Autofluorescent Biomolecules in Diptera: From Structure to Metabolism and Behavior

Light-based phenomena in insects have long attracted researchers’ attention. Surface color distribution patterns are commonly used for taxonomical purposes, while optically-active structures from Coleoptera cuticle or Lepidoptera wings have inspired technological applications, such as biosensors and energy accumulation devices. In Diptera, besides optically-based phenomena, biomolecules able to fluoresce can act as markers of bio-metabolic, structural and behavioral features. Resilin or chitinous compounds, with their respective blue or green-to-red autofluorescence (AF), are commonly related to biomechanical and structural properties, helpful to clarify the mechanisms underlying substrate adhesion of ectoparasites’ leg appendages, or the antennal abilities in tuning sound detection. Metarhodopsin, a red fluorescing photoproduct of rhodopsin, allows to investigate visual mechanisms, whereas NAD(P)H and flavins, commonly relatable to energy metabolism, favor the investigation of sperm vitality. Lipofuscins are AF biomarkers of aging, as well as pteridines, which, similarly to kynurenines, are also exploited in metabolic investigations. Beside the knowledge available in Drosophila melanogaster, a widely used model to study also human disorder and disease mechanisms, here we review optically-based studies in other dipteran species, including mosquitoes and fruit flies, discussing future perspectives for targeted studies with various practical applications, including pest and vector control.

Characterization and Phylogenetic Analysis of the Complete Mitochondrial Genomes of Two Tiny Necrophagous Phorid Flies, Metopina sagittata and Puliciphora borinquenensis (Diptera: Phoridae)

The mitochondrial genome is frequently used for species identification and phylogenetic studies. In this study, we first sequenced and annotated the complete mitochondrial genomes of two phorid species that are forensically important in buried or enclosed environments: Metopina sagittata (Liu) and Puliciphora borinquenensis (Wheeler). The complete mitochondrial genome sequences of M. sagittata and P. borinquenensis were 15,640 bp with an A+T content of 75.97% and 15,429 bp with an A+T content of 75.38%, respectively. Their circular genomes both contained 13 protein-coding genes (PCGs), 22 transfer RNA genes, 2 ribosomal RNA genes, and 1 control region located between rrnS and trnI which was 808 bp for M. sagittata and 746 bp for P. borinquenensis. All the PCGs of both species started with ATN codons except for cox1 which used TTG codon. In addition to the common stop codon TAA and TAG, the incomplete stop codon T was used in two PCGs (cox1 and nad4) of M. sagittata and five PCGs (cox1, cox2, cox3, nad5, and nad4) of P. borinquenensis. There were 3 and 10 mismatched base pairs in the tRNA secondary structures from M. sagittata and P. borinquenensis, respectively. Both maximum likelihood and Bayesian inference analyses indicated that Platypezidae and Phoridae are sister taxa. M. sagittata is closely related to P. borinquenensis within the subfamily Metopininae. This work enhances the databases of Phoridae genomes and contributes to the further study of species identification and phylogenetics of this family.

A Comparative Study of Circadian Rhythmicity and Photoperiodism in Closely Related Species of Blow Flies: External Coincidence, Maternal Induction, and Diapause at Northern Latitudes

This review compares adult locomotor activity rhythms and photoperiodic induction of diapause in 3 common species of blow fly, Calliphora vicina, Lucilia sericata, and Protophormia terraenovae. Activity rhythms were broadly similar in all 3 species, although P. terraenovae is much less sensitive to constant light inducing arrhythmicity. Photoperiodic induction of diapause, on the other hand, varies more widely between species. C. vicina and L. sericata overwinter in a larval diapause induced by autumnal short days (long nights) acting both maternally and directly upon the larvae. P. terraenovae, on the other hand, shows an adult (reproductive) diapause induced by short daylength and low temperature experienced by the larvae. In the Nanda-Hamner protocol, C. vicina shows 3 clear peaks of high diapause incidence in cycle lengths close to 24, 48, and 72 h, without dampening and therefore suggesting a photoperiodic mechanism based on a self-sustained circadian oscillator acting in a clock of the external coincidence type. Entrainment of the locomotor activity rhythm to extended Nanda-Hamner photocycles, as well as to LD cycles close to the limits of the primary range of entrainment, demonstrates that overt circadian rhythmicity may act as 'hands' of the otherwise covert photoperiodic system, as suggested by Bünning, nearly 8 decades ago. In 24 h LD cycles, both locomotor activity rhythms and the photoperiodic oscillator are set to constant phase (CT 12) at light-off, so that the photoperiodic clock measures changes in nightlength by the coincidence (or not) of dawn light with a 'photoinducible phase' late in the subjective night (at about CT 21.5 h) as photoperiod changes with the seasons. Apparent differences between quantitative and qualitative photoperiodic responses are discussed.