Phormia regina

Phormia regina
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Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Diptera
Family:	Calliphoridae
Genus:	Phormia
Species:	P. regina
Binomial name
Phormia regina Meigen, 1826
Synonyms
Musca regina Meigen, 1826

The species Phormia regina, more commonly known as the black blow fly, belongs to the blow fly family Calliphoridae. Although some authorities merge both the blow fly group (Calliphoridae) and the flesh fly group (Sarcophagidae) together in the family Metopiidae, key distinguishable physical traits allow for this separation.

Being a member of the order Diptera (the fly order), it is attributed by the presence of only its pair of fore wings while the pair of hind wings has been highly reduced to halteres. These halteres function in aiding in stability and maneuverability during flight. Wings of this fly are specialized having a sharp bend halfway through the wing and they are also known to have a well-developed calypter. Blow flies are about the size of a house fly or a little larger, many are metallic blue or green. Key characteristics of this species include black gena, mostly white calypteres and anterior thoracic spiracles that appear to be orange yellow due to being surrounded by bright orange setae.

Taxonomy

Phormia regina was described by the German entolomogist Johann Wilhelm Meigen in 1826. Its specific epithet is derived from the Latin regina 'queen'. Meigen's career works were mainly involved in the taxonomical aspect of identifying different species of Diptera. Spending a lot of time classifying species based on wing ventilation as well as, antennae, he discovered this was not sufficient to classify these dipteran species. He then reasoned that species can only identified by combination of characteristics; this technique later became known as the eclectic method.

Life cycle and development

The life cycle and development of Phormia regina is similar to that of most other dipteran species, in which females oviposit their eggs into a nutrient substrate and after eclosion (i.e. hatching), the larvae continue feeding 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.

Adult development

While in the wild, dung constitutes a majority of the nutritional intake used for sexual development in both male and female adults within this species, but diets consisting of higher protein contents will better facilitate mating conditions of both sexes. Female sexual maturity requires the completion of 10 stages of follicle development in the ovaries to produce eggs that are completely mature, and ovaries in females which have been deprived of a high-protein diet will not develop fully. Although it is possible for females on a diet of only dung to reach the final stage of sexual maturity, it takes much more time than if they were to feed exclusively on beef liver; even then, a lower percentage of those feeding on dung will have fully developed. For instance, an experiment by Stoffolano showed that 100% of females feeding exclusively on beef liver were able to reach the final stage of sexual development after 13 days, while only 78% of females were able to do so when feeding exclusively on pig dung over a 20-day period. Although some dipteran species will oviposit on dung, P. regina oviposits exclusively on carrion.

Furthermore, the neuroendocrine system in adult males, which controls their mating behavior, must be stimulated before they will mate with a female. Protein in the male diet is not necessarily needed for this stimulation, but higher percentages of females were successfully inseminated by male specimens which had been fed either dung or beef liver versus specimens with a diet of only sugar. Protein is not generally necessary for spermatogenesis in male flies, but it is paramount for accessory reproductive gland development, higher rates of copulation, and the capability of impregnating females. An additional study found a positive correlation between male head size and the size of the aedeagi (the external reproductive organs), which has been suggested as a possible reason for lower percentages of insemination between small males and large females within this species.

Larval development

Relatively few studies have been conducted on the adults of this species in comparison to those on larval development, mostly due to the importance of blow fly larvae in determining the post mortem interval (PMI) of corpses during investigations by forensic entomologists. For this reason, many researchers have done studies to discover how various environmental factors will affect the duration time of larval development in this species (as well as many others).

Because the larval life cycle of this species is dependent on a climate with temperatures ranging from 12.7°C (55°F) to 35 °C (95 °F), it tends to inhabit the northern regions of the United States during summer months and southern regions in the winter. Researchers have discovered,t at 40 to 45 °C, larval development occurs normally until the prepupal stage, at which point a majority of the larvae die and those that are able to pupate do not emerge as adults. The lowest temperature threshold for this species was found to be 12.5 °C and below; females will not oviposit at these temperatures. The highest rate of development (with survival) was a constant temperature of 35 °C, where the average time of adult emergence was 265 hours (about 11 days). Constant temperatures between 15 and 30 °C (at 5-degree increments) developed slower, with the coolest temperatures taking longest. Cyclic temperatures ranges of 25 to 35 °C and 15 to 25 °C proved to decrease the rate of development when compared to constant temperatures. (The cyclic temperature data were collected by placing specimens in an incubator which steadily alternated between the maximum and minimum temperatures of a particular 10- degree range (e.g. 25 to 35 °C). Each 10-degree fluctuation took place over a 12-hour span.)

Also, studies have been conducted to assess the effects of light exposure on developmental variability in larvae. Larvae exposed to cyclic photoperiods (shifting intermittently between 12 hours of light to 12 hours of darkness) have higher rates of development than larvae exposed to constant photoperiods (24 hours of light per day). These findings suggest darkness may be a stimulus for larval growth. However, the variations in light photoperiods mentioned above had no effect on pupal duration times.

Physiology

Like most other flies, the black blow fly feeds via sponging, having functional or nonfunctional mouthparts. They are known to feed on various foods, with emphasis on nectar, honey-dew, and the liquid products of decomposition. P. 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 h. 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. 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. Typically, blow flies will oviposit in the daytime due to the increase of temperature.

It is important to note the larval stage of the blowfly, due to its importance in forensics. 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

P. regina is a very important species in medicocriminal 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, most often of a violent nature, using two ideal approaches. One approach takes into account the general succession of arthropod communities to aid in estimation of post mortem interval, and the second factors in environmental influences in 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. The time elapsed since death before a corpse is discovered, referred to as post mortem interval, or PMI, is critical for investigations. 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 early stages of dipterans present may be used in determining the PMI by reverse estimation of the time it would take for eggs to have been deposited and larvae to have developed to the stage they were collected, while taking into account environmental factors. The use of maggot age and development can give a date of death accurate to a day or less, and is used in the first few weeks after death. Blow flies will lay their eggs on the corpse, usually in a wound, if present, or in any of the natural orifices. Therefore, after a single blow fly generation has been completed, the time of death is determined using the first method, that of insect succession.

Research is being conducted to further perfect the dating of a PMI. One study suggests 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 This knowledge of the effects of nocturnal temperatures on blow fly occurrence and oviposition behavior will lead to more accurate estimates of the PMI related to deaths, but more research is needed to assign a precise PMI.

Medicinal importance

Phormia regina is a flesh-eating fly not usually used for medical gain. However, the maggots from the black blow fly are used in a medical practice called maggot therapy. Maggot therapy is a type of biotherapy involving the intentional introduction by a health care practitioner of live, disinfected maggots into the skin and soft tissue wound of a human or animal for the purpose of selectively cleaning out only the necrotic tissue within a wound to promote wound healing. Maggot therapy dates back to the Mayan empire, but there are no actual records of use until the early 16th century.

The use of black blow fly maggots in maggot therapy is common. After the maggots have hatched, they are carefully monitored until they reach roughly 2 to 3 mm in length; at this point they are ready for the next step. Within 24 to 36 hours of hatching, the maggots are tested for their sterility; if they pass the rigorous tests, then they may be used in maggot therapy. These maggots are placed onto a sterile piece of gauze which is laid over the wound of the patient. The maggots will proceed through the gauze to the open wound, where they will then begin their work. When they are full-grown, they leave the wound and enter the gauze for the purpose of pupating. They are then removed with the waste gauze and disposed of properly.

The use of maggot therapy is not limited to humans, but it is not a common practice with livestock. Using maggot therapy with livestock could be beneficial in many ways. In dairy cattle, it would eliminate the need to destroy milk contaminated with antibiotics. The use of antibiotics on horses can affect its gastrointestinal flora which may result in colitis. Maggot therapy would eliminate this additional stress when treating equine wounds. Treatment options for the animals of people who cannot afford expensive surgeries would be a new possibility for veterinarians using this therapy.

Further reading

• Anderson, G.S. Forensic Entomology: the use of insects in death investigations.
• Byrd, J.H. and J.C. Allen. 2001. The development of the black blow fly, Phormia regina (Meigen). Forensic Sci. Int. 120: 79-88.
• Byrd, J. H., and J. L. Castner. 2001. Forensic entomology : The utility of arthropods in legal investigations. CRC Press, New York.
• Catts, E. P., and M. L. Goff. 1992. Forensic entomology in criminal investigations. Ann. Rev. Entomol. 37 : 253-272.
• Fletcher F., Haub J.G. Digestions in blowfly larvae, Phormia regina meigen, used in the treatment of osteomyelitis. Ohio State University.
• Greenberg, B. 1990. Nocturnal oviposition behavior of blow flies (Diptera: Calliphoridae). J. Med. Entomol. 27 (5) : 807-810.
• Kirkpatrick, R. S. Nocturnal light and temperature influences on necrophagous, carrion-associatingblow fly species of forensic importance in Central Texas. TAMU Undergrad. J. Sci.
• Nabity, P.D., L.G. Higley, and T.M. Heng-Moss. 2007. Light-Induced Variability in Development of Forensically Important Blow Fly Phormia regina (Diptera: Calliphoridae). J. Med. Entomol. 44(2): 351-358.
• Rognes, Knut. 1991. Blowflies (Diptera, Calliphoridae) of Fennoscandia and Denmark. E.J. Brill/Scandinavian Science Ltd., 272pp.
• Stoffolano, J.G. Jr, E.Y. Gonzalez, M. Sanchez, J Kane, K Velázquez, A.L. Oquendo, G. Sakolsky, P. Schafer, and C.-M. Yin. 2000. Relationship Between Size and Mating Success in the Blow Fly Phormia regina (Diptera: Calliphoridae). Ann. Entomol. Soc. Am. 93(3): 673-677.
• Stoffolano, J.G. Jr, M.-F. Li, J.A. Sutton Jr, and C.-M. Yin. 1995. Faeces feeding by adult Phormia regina (Diptera: Calliphoridae): impact on reproduction. Medical and Veterinary Entomology 9, 388-392.
• Watson L., Dallwitz M.J., British Insects: the Families of Diptera.
• Whitworth, Terry. 2006. Keys to the Genera and Species of the Blow Flies (Diptera:Calliphoridae) of America North of Mexico. PROC. ENTOL. SOC. WASH. 30 June. 108(3), pp. 629–725