Phormia

Phormia regina, the black blow fly, belongs to the blow fly family Calliphoridae and was first described by Johann Wilhelm Meigen. It is the only species in the genus Phormia. The black blow fly's wings are specialized with a sharp bend. These flies also have well-developed calypters. Blow flies generally are about the size of a house fly or a little larger, and many are metallic blue or green in color. Key characteristics of this species include black gena, mostly white calypters, and anterior thoracic spiracles that appear to be orange yellow due to being surrounded by bright orange setae. Phormia regina is especially important to forensic entomology. Female P. regina, like other blow flies in the family Calliphoridae, oviposit their eggs on carrion, where they hatch. The larvae develop through three instar stages until pupation. Adult black blow flies aggregate on feces in order to mate. The success of these mating interactions has been studied and appears to be related to size and diet of the adult flies. Following successful mating encounters, the adult females are then attracted to decaying material rather quickly for oviposition, allowing forensic entomologists to use development stages of larvae as a clue in determining an approximate time of death. P. regina are extremely common in the United States and other areas in North America.…

Phormia regina, the black blow fly, belongs to the blow fly family Calliphoridae and was first described by Johann Wilhelm Meigen. It is the only species in the genus Phormia. The black blow fly's wings are specialized with a sharp bend. These flies also have well-developed calypters. Blow flies generally are about the size of a house fly or a little larger, and many are metallic blue or green in color. Key characteristics of this species include black gena, mostly white calypters, and anterior thoracic spiracles that appear to be orange yellow due to being surrounded by bright orange setae. Phormia regina is especially important to forensic entomology. Female P. regina, like other blow flies in the family Calliphoridae, oviposit their eggs on carrion, where they hatch. The larvae develop through three instar stages until pupation. Adult black blow flies aggregate on feces in order to mate. The success of these mating interactions has been studied and appears to be related to size and diet of the adult flies. Following successful mating encounters, the adult females are then attracted to decaying material rather quickly for oviposition, allowing forensic entomologists to use development stages of larvae as a clue in determining an approximate time of death. P. regina are extremely common in the United States and other areas in North America. Combined with their importance in forensic entomology, these flies have been relatively well studied, particularly for variables affecting their development.

Taxonomy

Phormia regina was described by the German entomologist Johann Wilhelm Meigen in 1826. Its specific epithet is derived from the Latin word regina meaning 'queen'.

Description

Phormia regina adults are metallic blue or green in color and have a distinctive set of orange setae near the anterior thoracic spiracle. They are also recognizable by their black gena (the side of the head below eye level), mostly white calypteres, and the distinctive bend in their wings.

Life history

The life cycle and development of Phormia regina is similar to that of most other Dipteran species, in which females oviposit their eggs onto a nutrient substrate. Then, after hatching, the larvae feed throughout three instar stages until they have stored up enough calories to commence pupation and finally emerge as adult blow flies. Each transition from first, second, and third instar is marked by a molt, and eventually the third-instar larvae develop sclerotized (hardened) casings which envelop and protect them throughout metamorphosis. The entire genome of P. regina has been sequenced so that it may serve as a reference genome that can be used in comparison with other Calliphoridae species. This fly has a chromosome number of 2n=12. The sex chromosomes of P. regina are a heteromorphic chromosome pair, meaning they have two morphologically distinct chromosomes that remain a homologous chromosome pair. Picard and Wells used amplified fragment length polymorphisms (AFLP) to create genetic profiles of P. regina flies collected from different regions to compare both within region and across region relatedness. They discovered adult flies take from the same corpse showed high relatedness, but between regions genetic variability was high. They suggest these findings may be especially important to forensic entomology with respect to determining if a recovered body has moved locations by comparing AFLP data across individual P. regina.

Physiology

Phormia regina, like other flies, is poikilothermic: the growth and development of the fly is dependent on temperature. At room temperature, the egg to pupal stage lasts about 6–11 hours. With an increase in temperature of the surrounding environment, metabolic rates of the blow fly typically increase, causing an increase in the rate of growth and development. However, this species is intolerant to warmer temperatures, unlikely to survive to adulthood at temperatures of 40 °C or greater. This observation provides an explanation as to why the species cannot survive the summer months in southern regions of the US. The adult organism's activity becomes inhibited by temperatures lower than 12.5 °C. In addition to an increase in the growth and development, temperature also has a profound impact on female oviposition. It is key to note the fluctuations between diurnal and nocturnal temperatures. The larvae have posterior spiracles, small openings on the back used for the intake of oxygen. Larvae are also equipped with mouth hooks used for the physical breakdown of proteins when feeding, while proteolytic enzymes are used for chemical breakdown of these proteins.

Forensic importance

Phormia regina is a very important species in medico-criminal entomology, an area in forensic entomology which uses entomologists to aid with arthropod evidence in criminal investigations. This aspect of forensic science stresses using arthropod evidence in solving crimes, often of a violent nature, through two ideal approaches to estimate post mortem interval (PMI). The first approach accounts for the general succession of arthropod communities, and the second considers environmental influences on the development of arthropods. With knowledge of the regional insect fauna and times of carrion colonization, the insect gathering associated with the remains can be analyzed to determine a window of time in which death took place. PMI is a critical aspect of criminal investigations following recovery of a corpse. PMI relies on an entomologist's ability to correlate the species or stage of development of arthropods, in this case P. regina, to an approximation of the elapsed period between a person's death and the discovery of his/her body. Blow flies are usually the first insects to colonize a body, frequently within minutes after death. P. regina adults and larvae are attracted to the body because, during decomposition, the remains go through rapid physical, biological, and chemical changes. If a corpse is found, the presence of Dipteran larvae may be used to suggest PMI by estimating the time it would have taken for eggs to have been deposited and larvae to have developed to the stage they were collected, while taking into account environmental factors. Blow flies will lay their eggs on the corpse, usually in a wound, if present, or in any of the natural orifices, and the maggot age can give a date of death accurate to a day or less, and is used in the first few weeks after death. Research is being conducted to further perfect the dating of a PMI. One study suggests that P. regina occasionally oviposits on carrion at night only when certain conditions are met. A similar study found a combination of artificial lighting, warm temperatures, and the onset of low-pressure atmospheric conditions encourages nocturnal oviposition in P. regina Other studies suggest P. regina preferentially distribute their eggs during the day. Confirming the preference for daytime or nighttime oviposition in P. regina could aid in increasing the accuracy of PMI determination, and the disagreement necessitates more experimentation to investigate this environmental effect.

References

Further reading

Anderson, G.S. Forensic Entomology: the use of insects in death investigations. Byrd, J. H., and J. L. Castner. 2001. Forensic entomology : The utility of arthropods in legal investigations. CRC Press, New York. Rognes, Knut. 1991. Blowflies (Diptera, Calliphoridae) of Fennoscandia and Denmark. E.J. Brill/Scandinavian Science Ltd., 272pp. Watson L., Dallwitz M.J., British Insects: the Families of Diptera.

Text derived from https://en.wikipedia.org/w/index.php?oldid=1369577598 under CC BY-SA 4.0; modifications have been made.