Protophormia terraenovae is commonly called northern blowfly, blue-bottle fly or blue-assed fly (blue-arsed fly in British English). It is distinguished by its deep blue coloration and large size and is an important species throughout the Northern Hemisphere. This fly is notable for its economic effect as a myiasis pest of livestock and its antibiotic benefits in maggot therapy. Also of interest is P. terraenovaes importance in forensic investigations: because of their temperature-dependent development and their prominent presence on corpses, the larvae of this species are useful in minimum post-mortem interval (mPMI) determination.
Taxonomy Protophormia terraenovae, of the family Calliphoridae, was named and first described by French entomologist André Jean Baptiste Robineau-Desvoidy in his 1830 "Essai sur les myodaires". Its genus is shared by one other fly, Protophormia atriceps. Both flies are a dark, undusted, metallic blue-green-black. P. terraenovae is differentiated from P. atriceps by its flat face, plumose arista, and by up to 2 additional pairs of setae along the margin of the scutellum.Whitworth, Terry. "Keys to the Genera and Species of Blow Flies (Diptera: Calliphoridae) of America North of Mexico. Proc. Entomol. Soc. Wash. 108(3). 2006. P. terraenovaes specific epithet is translated from the Latin as "of the New World".
The oldest-known specimens of P. terraenovae pupae were identified in 1973 within the fossilized skull of a steppe wisent. The bison skull, estimated to date from the late Eemian period, was excavated from the site of a new sluice for the Brussels-Rupel Canal in Zemst, Belgium. The specimens, although approximately 75,000 years old, are identical in form to the pupae of the modern species.Gautier, A. & H. Schumann. “Puparia of the subarctic or black blowfly Protophormia terraenovae (Robineau-Desvoidy, 1830) in a skull of a late Eemian (?) bison at Zemst, Brabant (Belgium).” Palaeogeogr., Palaeoclimatol., Palaeoecol. 14 (1973): 119-125.
Morphology
Adult The adult Protophormia terraenovae, one of the larger species of calliphorids, measures between 7 and 12 mm in length.Byrd, Jason, and James Castner (2001). Forensic Entomology: The Utility of Arthropods in Legal Investigations, CRC Press, New York. . It is characterized by a black to brown anterior thoracic spiracle,Wall, Richard, and David Shearer. Veterinary Entomology: Arthropod ectoparasites of veterinary importance. London: Chapman & Hall, 1997. a black basicosta, brown wing veins, and dark calypters. Upper calypters sprout black setae. While the thorax and abdomen of P. terraenovae can range in color from dark purple to dark green, the head and legs of this fly are black. Postocular setae are short but prominent; the palpi are yellow or dusky brown.Rognes, Knut. "Blowflies (Diptera, Calliphoridae) of Fennoscandia and Denmark." Fauna Entomologica Scandinavia 24. Leiden: E.J. Brill/Scandinavian Science Press Ltd. 1991.
Sexes of the species are easily distinguished by the width of the space between the eyes, the frons: that of the female is .386 times the width of the head, while the frons of the male is only .140 times the head width. Chaetotaxy, the study of setae arrangement, is also useful for determination of sex—for example, the male lacks the fronto-orbital, lateroclinate setae found in the female. These setae are located just at the edge of the frons, near the upper portion of the complex eyes.
Larvae Protophormia terraenovae larvae are tiny and white, with 12 segments. Length varies by larval age, with the first instar growing up to 2.63 mm and the third, by contrast, as long as 11.87 mm. In the third instar, the last segment is adorned with pointed tubercles, and segment 10 exhibits dorsal spines along its posterior margin. The latter characteristic distinguishes P. terraenovae, 3rd instar, from a similar calliphorid, Phormia regina.Erzinçliolu, Y. Z. “The larvae of the species of Phormia and Boreellus: Northern, cold-adapted blowflies (Diptera: Calliphoridae).” Journal of Natural History, 22.1(1988):11-16.
Development Being of the order Diptera, Protophormia terraenovae is holometabolous in its development, meaning it experiences dramatic changes from immature to adult. Protophormia terraenovae undergoes three instars, a pupal stage, and finally an adult stage.
First instar larvae obtain a liquid diet from orifices or wounds of a body. The instars that follow digest the body itself. Among the first to colonize, Calliphoridae species are found on the body almost immediately. As eggs hatch into the first larval stage, P. terraenovae begins feeding and increases in size, limited by its chitinous outer cuticle. As P. terraenovae larvae molt into the second instar, feeding intensifies: with larger and more developed mouthparts, second instars are able to break down tougher body tissues. Warren, Jodie-Ann. "The Development of Protophormia terraenovae at Constant and Fluctuating Temperatures. . Simon Fraser University, 1999."
The third instar is unique, consisting of several substages. First, the larvae feed until they reach their maximum size. Next, larvae clear their crops. In this prepupal stage, also called the wandering stage, the maggots seek a dry, safe area for pupation. During the pupal stage, the outer cuticle hardens and tans into a dark brown color, gradually darkening with age. Finally, metamorphosis into the adult is completed with the shedding of the pupal casing and the emergence of the fly.
The time of development between instars to pupae to adult differs depending on temperatures. The mean duration of development, at constant pressure and 25 °C, between oviposition and hatching is 1.83 days. From first to second instar, approximately 2.92 days pass. About 6.17 days pass between the second and third instar, and 8.0 days between the third instar and the post-feeding stage. The wandering maggot takes around 9.67 days to reach the pupal stage. Lastly, emergence of this blowfly occurs about 15.83 days after pupation. In fluctuating conditions such as those around crime scenes, there is a tendency for development to slow down. Under-approximation of age is therefore a common mistake.Clarkson, Colin A., Niki Hobischak, and Gail Anderson. “Developmental rate of Protophormia terraenovae (R-D) raised under constant and fluctuating temperatures, for use in determining time since death in natural outdoor conditions, in the early postmortem interval.” 2005.
The development of P. terraenovae is inversely related to temperature. Studies at (15, 20, 25, 30, 35)°C were performed, and the minimal duration of development from oviposition to adult ranges from 9.19 ± .3 days at 35 °C, to 37.78 ± 2.96 days at 15 °C. The minimum development threshold for total immature development is 8.95 °C. The overall thermal constant (K) for P. terraenovae is 240.2 ± 9.3 day-degrees above threshold. The inverse relationship and regression of development from oviposition to pupation resulted in a 9.8 °C threshold for the species.Grassberger, Martin, and Christian Reiter. "Effect of Temperature on Development of the Forensically Important Holarctic Blow Fly Protophormia terraenovae (Robineau-Desvoidy) (Diptera: Calliphoridae)." Forensic Science International 128 (2002): 177-182.
Pupation occurs on or within .5 meters of the decaying body. The duration of the pupal stage is relatively long compared to the rest of development, inactively occupying 43% of P. terraenovaes total cycle. The third instar larva spends 13% of its cycle in feeding stage and 22% in post-feeding stages.E. Gaudry, C. Blais, A. Maria, C. Dauphin-Villemant. Study of steroidogenesis in pupae of the forensically important blow fly Protophormia terraenovae (Robineau-Desvoidy) (Diptera: Calliphoridae). Forensic Science International. 160.1(2006): 27-34.
Geographic distribution Protophormia terraenovae has a Holarctic distribution, meaning the species is found throughout the northern hemisphere. The fly is common in cool regions and, being "the most cold tolerant of all calliphorid species," can withstand extreme temperatures. P. terraenovae can be found as close as 550 miles from the North Pole and is abundantly found in the Arctic.Smith, K.G.V. A Manual of Forensic Entomology. London, British Museum (Natural History). 1986.
In North America, P. terraenovae can be found from Mexico to Canada. Appearance of this species is rare and mostly confined to the winter months in warm regions such as Texas and Florida. P. terraenovae is a spring or summer species in high latitudes and elevations.
Importance
Medical Maggot debridement therapy (MDT) is commonly used for the cleansing and disinfecting of chronic wounds containing necrotic flesh. Various studies have shown that MDT is effective in treating wounds that have failed to heal. Effective MDT species consume necrotic tissue while cleansing the wound.Kočišová, A., J. Pistl, R. Link, E. Čonková, and M. Goldová. "Maggot Debridement Therapy in the Treatment of Footrot and Foot Scald in Sheep." Acta Vet. Brno 75 (2006): 277-81. Protophormia terraenovae is among the few blowfly species that fit these criteria. The larvae of most blowflies are necrophagous, meaning they develop in the bodies of dead vertebrates where they consume necrotic tissues. Because the majority of other blowfly larvae consume both necrotic and healthy tissues, P. terraenovae is an important species. P. terraenovae is also known to produce antibiotics during feeding: the secretions of P. terraenovae larvae are effective in fighting infections involving Streptococcus pyogenes and Streptococcus pneumoniae.Sherman, R. A., M. J. R. Hall, and S. Thomas. “Medicinal Maggots: an Ancient Remedy for Some Contemporary Afflictions.” Annu. Rev. Entomol. 45(2000):55-81.
The main concern with the use of MDT is sepsis. P. terraenovae is blamed for five reported bloodstream infections.Dimarcq, J.L., D. Zachary, J.A. Hoffmann, D. Hoffmann, and J.M. Reichhart. "Insect immunity: expression of the two major inducible antibacterial peptides, defensin and diptericin, in Phormia terranovae." EMBO J. 9: 2507-515. To prevent infection, P. terraenovae maggots must be raised in vitro under sterile conditions. Provided these precautions are taken, the use of P. terraenovae on chronic wounds appears to remain safe and efficient in wound treatment.
Economic As a species of the blowfly family Calliphoridae, Protophormia terraenovae causes economically important myiasis in livestock and, occasionally, in humans. It also affects other populations of Diptera due to the predacious nature of its larvae when competing for necrotic tissue. P. terraenovae larvae have also been known to behave cannibalistically.Green, A. A. "The Control of Blowflies Infesting Slaughter-Houses I. Field observations of the habits of blowflies." Annals of Applied Biology 38 (1951): 475-494.
Myiasis due to Protophormia terraenovae has been reported in both wild and domestic animals, but it most commonly affects livestock. Species usually oviposit on carrion, but are capable of oviposition in the wounds of livestock and wild animals. Thus, P. terraenovae acts as a secondary invader in causing myiasis.Samuel, William M., A. A. Kocan, Margo J. Pybus, and John W. Davis, eds. Parasitic Diseases of Wild Mammals. 2nd ed. Grand Rapids: Blackwell Professional, 2001. Commonly referred to as 'wound strike', lesions are foul smelling ulcers that are filled with larvae. Animals infected with myiasis may die from toxemia and sepsis.Scott, Danny W., and William H. Miller. Equine Dermatology. Philadelphia: Saunders, 2003.