Case report on Cochliomyia hominivorax (Coquerel, 1858) and Co. macellaria (Fabricius, 1775) (Calliphoridae, Diptera) myiasis prior to death: Implications on postmortem interval estimation.

The most important contribution of forensic entomology is the estimation of the postmortem interval (PMI) or time since death. The forensic entomologist assumes that the biological clock of necrophagous insects that develop by feeding on cadaver tissues begins when the victim's biological clock is turned off. However, tissues can be invaded while the host is still alive (called myiasis), so the period of activity of necrophagous insects would not be indicative of PMI. The aim of this work was, through the presentation of a case report, to highlight the importance of expertise in the identification of necrophagous species associated with a corpse and their type of relationship in order to avoid an erroneous estimation of PMI. The corpse of a woman, missing for 14 days, was found outdoors in a small river 15 cm deep. Her corpse had numerous lesions infested with dipteran larvae that were collected during autopsy. Entomological evidence included second and third instar larvae of Cochliomyia hominivorax and Co. macellaria. The obligate parasitic nature of Co. hominivorax as a primary producer of myiasis and secondary of Co. macellaria allowed us to establish the time when the victim was still alive and from there to estimate the PMI.

Blow flies, synanthropy and sex ratio: Are the deviations in the sex proportion linked to human transformation of landscapes?

In most species, several factors like time of emergence, age at maturation, reproductive life span, survival of males and females, mating behavior, differential resource use, and migration patterns may affect the adult sex ratio. Anthropogenic landscape transformation is known to change diversity, favoring colonization by exotic species but other populational parameters, such as the sex ratio, have not been assessed. The aim of the present study was to describe the sex-ratio patterns of adult necrophagous blow flies captured using carrion-baited traps along habitats representing different levels of human impact. We describe the sex bias for four species: the exotic Chrysomya albiceps, Chrysomya megacephala, Chrysomya putoria, and the native Cochliomyia macellaria. Three types of habitats were selected: highly anthropized (urbanized), moderately anthropized (rural), and native forest (natural) within a humid subtropical ecoregion in Northeastern Argentina. We found an overall trend to female bias among the four species when considering the total number of each sex. However, our study showed a changing sex-ratio pattern along the gradient of human influence. Our results indicate that a higher likelihood of trapping more males in unsuitable habitats seems to be widespread among blow flies. Urban exploiters, such as Ch. megacephala and Ch. putoria, locally shifted their trends, becoming male-biased in natural habitats. The opposite trend was detected in the urban avoider Co. macellaria (which shifted to male-biased in urban habitats). The exception was Ch. albiceps, whose sex proportion did not shift to a male-biased sex ratio. The results of this study highlight the changing sex-ratio patterns displayed by Calliphoridae in response to different conditions along a human-influence gradient. The biological traits and underlying mechanisms promoting the intraspecific changes of the sex ratio are discussed.

Trophic interactions between parasitoids and necrophagous flies in Central Argentina.

Larvae of necrophagous flies in the families Calliphoridae, Sarcophagidae and Muscidae are the main exploiters of decaying organic matter. Knowledge of insect species associated with each stage of decay can be used to estimate the time since death in the crime scene. Dipteran larvae are attacked by a rich community of parasitoids, including species of Braconidae, Ichneumonidae and Pteromalidae (Hymenoptera: Parasitica). This study examined the parasitic complex associated with flies of forensic and sanitary importance in the city of Córdoba (Argentina). Sampling was conducted at two sites with different urbanization levels from December 2012 to March 2013; parasitoids were collected using fly traps baited with beef liver. Rates of parasitism and of parasitized pupae were estimated and species composition was analyzed for both communities. Sarcophagidae was the most abundant family, represented by two species, followed by Calliphoridae. Nasonia vitripennis Ashmead (Hymenoptera) was the most abundant species and was collected from a wider variety of hosts. To the best of our knowledge, this is the first study providing accurate information about trophic interactions between calyptrate dipteran species and their hymenopteran parasitoids in central Argentina.

Seasonal structure and dynamics of sarcosaprophagous fauna on pig carrion in a rural area of Cordoba (Argentina): their importance in forensic science.

Four experiments, one in each season, were carried out during 2004 in a rural area of Córdoba, central Argentina. Two pigs (Sus scrofa L.), weighing approximately 8 kg each, were used in each of the four experiments. The animals were killed by a sharp blow to the head and immediately placed in an appropriate arthropod trap. One pig was placed in the shade and the other under direct sunlight. This research was conducted to determine the seasonal structure and dynamics of arthropods that constitute the sarcosaprophagous community in a given area of the central region of Argentina. The decomposition process was divided into five stages: fresh, bloated, decay, advanced decay and dry. The duration of each stage varied in different seasons, showing that the temperature and humidity are the most important variables that influence this process. A total of 51,500 adults and 36,909 immature were collected. More than 80% of the specimens collected belong to Insecta, and within this, Diptera were the most abundant order. The flies were mainly represented by adults and immature of the following species: Chrysomya albiceps (Wiedemann) (Calliphoridae), Musca domestica Linnaeus (Muscidae) and Fannia femoralis (Stein) (Fanniidae). Coleoptera were mainly represented by adults and immature of the species Creophilus maxillosus (Linnaeus) (Staphylinidae) and Dermestes maculatus (Geer) (Dermestidae). More than 50% of hymenopteran fauna collected belong to Formicidae. The trophic levels associated with the decomposition of the remains included five categories: necrophagous, parasites and predators of the necrophagous species, omnivores, opportunists and adventives. During faunal succession a strong dominance of the necrophagous species of the family Calliphoridae and Muscidae was observed, mainly during the early stages of decay process in all seasons.

Species composition and seasonal succession of saprophagous calliphorids in a rural area of Córdoba: Argentina.

During 2004, four experiments were carried out, one each season, in order to determine the species composition and seasonal dynamics of Calliphoridae in a rural area of Córdoba (Argentina). Two pigs (Sus scrofa L.), weighing approximately 8 Kg each, were used in each experiment. They were killed with a blow to the head and immediately placed in a variant of the Schoenly et al. (1991) trap. One pig was exposed in the shade and the other one under direct sunlight. The insect fauna was collected daily during the four first weeks and every two or three days thereafter. A total of 16.609 adults of Calliphoridae were collected, and later on identified as one of the following seven species: Chrysomya albiceps (Wiedemann), Chrysomya megacephala (Fabricius), Phaenicia sericata (Meigen), Phaenicia eximia (Wiedemann), Cochliomyia macellaria (Fabricius), Sarconesia chlorogaster (Wiedemann) and Calliphora vicina Robineau-Desvoidy. C. albiceps was the dominant species in summer, autumn and spring, being replaced in winter by C. vicina, S. chlorogaster and P. sericata. The analysis of the seasonal distribution of the species revealed that the greater incidences are in the months of summer, autumn and spring.

Species composition and seasonal succession of saprophagous calliphorids in a rural area of Córdoba: Argentina

During 2004, four experiments were carried out, one each season, in order to determine the species composition and seasonal dynamics of Calliphoridae in a rural area of C¢rdoba (Argentina). Two pigs (Sus seroja L.), weighing approximately 8 Kg each, were used in each experiment. They were killed with a blow to the head and immediately placed in a variant of the Schoenly et al. (1991) trap. One pig was exposed in the shade and the other one under direct sunlight. The insect fauna was collected daily during the four first weeks and every two or three days thereafter. A total of 16.609 adults of Calliphoridae were collected, and later on identified as one of the following seven species: Chrysomya albiceps (Wiedemann), Chrysomya megacephala (Fabricius), Phaenicia sericata (Meigen), Phaenicia eximia (Wiedemann), Cochliomyia macellaria (Fabricius), Sarconesia chlorogaster (Wiedemann) and Calliphora vicina Robineau-Desvoidy. C. albiceps was the dominant species in summer, autumn and spring, being replaced in winter by C. vicina, S. chlorogaster and P. sericata. The analysis of the seasonal distribution of the species revealed that the greater incidences are in the months of summer, autumn and spring.