POPULATION DYNAMICS OF CALYPTRATE DIPTERA (MUSCIDAE AND SARCOPHAGIDAE) AT THE RIO-ZOO FOUNDATION, RIO DE JANEIRO, RJ, BRAZIL

Twenty-seven species of calyptrate muscoids (Muscidae and Sarcophagidae) were collected from December 1993 to November 1994 with wind oriented traps (W.O.T.) baited with decomposing beef liver at the Rio de Janeiro Zoo. The most abundant species found were Musca domestica (57.84%), Peckia chrysostoma (28.16%), Ophyra aenescens (17.11%), Oxysarcodexia thornax (17.82%), Synthesiomyia nudiseta (13.05%), and Oxysarcodexia diana (14.52%).


INTRODUCTION
Muscoids dipterous have always been associated with human and domestic animals due to the abundance of food resources found in stables and domestic garbage.These flies are of major concern for veterinary medicine due to their capacity to act as a vector of several pathogenic or-ganisms such as protozoa cysts, helminth parasites, enteropathogenic bacteria, and enterovirus (Root, 1921;Nuorteva, 1959;Greenberg, 1973).
Zoological gardens offer excellent conditions for breeding calyptrates dipterous due to abundant food resources and breeding places like feces and food leftovers of animal and vegetable origin (D'Almeida, 1989;Oliveira et al., 1999).
The objective of this study was to investigate frequency, abundance, and season of Sarcophagidae and Muscidae at the Rio de Janeiro Zoo (Rio-Zoo).

MATERIAL AND METHODS
To capture adult flies, six wind oriented traps (W.O.T.), described by Broce et al. (1977) and latter modified by Oliveira et al. (1982), were placed from 1.00 to 1.50 meters from the ground at three different spots inside the zoo: site 1, near the veterinary and biological facilities; site 2: next to the giraffe and zebra enclosure; and site 3, next to the repair shop and the deer park.All of the traps were set from December 1993 to November 1994.To attract adult flies, a plastic recipient (11 cm diameter × 7 cm height) containing 500 g of rotting beef liver (5 days old) was placed inside each trap.The bait was changed every week.
Three times a week, the traps were checked and all captured specimens were killed with aerosol insecticide (pyrethroid), removed from the traps, and taken in plastic bags to the Laboratory of Biology and Control of Vector Insects, Biology Department, Oswaldo Cruz Institute, Fiocruz.After being identified and quantified, all samples were deposited in the collection of that laboratory.
Each month the number of captured flies was correlated with temperature, relative humidity, and precipitation (correlation of Pearson), obtained from the Meteorological Station of the Federal University of Rio de Janeiro.

RESULTS AND DISCUSSION
The abundance and relative frequency of the captured species of Muscidae and Sarcophagidae are shown in Tables 1 and 2, respectively.
Among the muscids, Musca domestica (Linnaeus, 1758) was the most abundant species, totaling 54.84% (2,224 captured specimens).The population peaks occurred in April, May, and July (Fig. 1) and the species was most frequent during autumn (Table 1).Even though the differences among the sampling sites have not been analyzed, this species was more common at site 2, next to the giraffe and zebra enclosure.This could be related to its proximity to the Evaristo de Morais prison with its high population density and to an enormous quantity of elephant feces.Following Greenberg (1971), M. domestica was initially coprophagous and adapted to ungulate excrements.Later, with the synantropization process, it became adapted to several substrates.Nunes et al. (1991) and Keiding (1976) showed that this fly has ample geographic distribution and great epidemiological importance, due to its capacity to adapt to manmade conditions and use several substrates as food and breeding sites, as well as being a potential mechanical vector for a great number of pathogens.Ophyra aenescens (Wiedemann, 1830) was the second in abundance with 658 collected specimens.The populational peaks were in April and May (Fig. 1) with a higher frequency in autumn (Table 1).Linhares (1979) found that O. aenescens had a high synanthropic index among the muscidae collected in Campinas, SP, and disagrees with d'Almeida (1983) who reported the preference of this fly for uninhabited areas of Rio de Janeiro.Bohart & Gressit (1951) reported the variety of substrates that can be used by this muscoid, including fresh human feces, carcasses, and rotting vegetables.Salviano (1996) found this species in the dead body of Sus scrofa in an urban Rio de Janeiro area and emphasized its importance in forensic entomology.
Only 2.93% of the collected muscids were of the Atherigona orientalis (Schiner, 1868) species (Table 1).This contrasts with the results of d'Almeida (1983 and 1988) who found a high abundance of this species in rural and urban areas of Rio de Janeiro.Probably the present result is due to the trap wire width that permitted the escape of the flies as well as to the bait type used.Povolny (1971) relates that A. orientalis can grow at several substrates ranging from carcasses and human feces to rotting vegetables and urban garbage.D 'Almeida (1988) reported the species preference for vegetable substrates, especially fruits.
Among the sarcophagids, Peckia chrysostoma (Wiedemann, 1830) was the most common species with 853 specimens; it was more frequent during the summer (Table 2).D'Almeida (1983) also found a great abundance of this fly in the urban Rio de Janeiro area.
Eleven species from Oxysarcodexia genus were captured, making up 44.8% of total collected sarcophagids.Among the genus, the most abundant species was O. thornax (Walker, 1849) being the second most collected among the sarcophagids (540 specimens) (Table 2).The population peak of O. thornax was registered in January and February (Fig. 2).This species was also abundant in Curitiba, Belo Horizonte, Campinas, and Rio de Janeiro as described by Ferreira (1975), Dias (1983), Mendes (1991), andSalviano (1996), respectively.Both Mendes (1991) in Campinas and Dias (1983) in Belo Horizonte, observed the attraction of these flies to human feces and chicken guts.In Rio de Janeiro, D' Almeida (1983) found that the flies were most attracted to fish.Salviano (1996) reported the presence of 1st and 2nd instar larvae of O. thornax developing in accumulated feces in the anus of a carcass of Sus scrofa, although no larvae was found in the tissues.Following Lopes (1946), this genus is characteristic of the Neotropical region and the greatest number of species is found in Brazil where it develops preferentially in feces.Oxysarcodexia diana (Lopes, 1933) was the third most abundant species among the Sarcophagidae (Table 2).The population peak occurred in January and February (Fig. 2).D'Almeida (1983) showed that this dipteran has a greater preference for urban areas of Rio de Janeiro although, in Belo Horizonte, Dias (1983) did not find this result.Both of these authors observed that feces were the most attractive bait for this species.The abundance of this and other sarcophagids, like O. thornax, can be related to the high abundance of feces in animal enclosures which favor larval development.
Sarcodexia lambens (Walker, 1861) was also abundant in Rio de Janeiro, predominating during winter months (Table 2).In a study conducted in Rio de Janeiro (D'Almeida, 1983), this species occurred in greater abundance in urban areas and the most attractive bait was fish.However, in Campinas (Linhares, 1981) and Belo Horizonte (Dias,1983) the species was more abundant in uninhabited areas.
Pattonella intermutans (Thonson, 1869), a frequent species in Rio de Janeiro, was more abundant in the spring (Table 2).In Rio de Janeiro (D'Almeida, 1983) and in Belo Horizonte (Dias, 1983) this species was more common during the summer.According to D'Almeida (1983), this species shows an aversion to inhabited areas; its most attractive baits were fish and beef liver.Salviano (1996) emphasized the importance of this species for forensic studies in Rio de Janeiro State.Fig. 3 shows the monthly climatological data observed during the study.With respect to the correlation between monthly frequency of species collected and weather factors, a significant positive correlation appeared between relative humidity and the abundance of M. domestica (r = 0.54; n = 12; p < 0.05) and O. aenescens (r = 0.53; n = 12; p < 0.05).
A positive correlation was also observed between O. diana and temperature (r = 0.52; n = 12; p < 0.05).However, the abundance of P. chrysostoma was negatively correlated with precipitation (r = -0.59;n = 12; p < 0.05).There were no significant correlation between the other species and weather factors.
M. domestica, O. aenescens, and S. nudiseta have a population peak in April (Fig. 1).There was a huge build-up of garbage during this month due to collecting difficulties in Rio de Janeiro.This underscores the relation between these muscoids and urban garbage.
Zoos have peculiar characteristics attractive to the dipterofauna since they resemble rural habitats due to the feces volume produced daily.
They also constitute ideal places not only for studying population dynamics studies but also for evaluating the epidemiological aspects of pathogenic transmission.

Fig. 2 -
Fig. 2 -Monthly frequency of Peckia chrysostoma, Oxysarcodexia thornax, and Oxysarcodexia diana captured from December 1993 to November 1994 with wind oriented traps, baited with decomposing beef liver in the Rio de Janeiro Zoo.

TABLE 2 Relative and absolute frequencies of the Sarcophagidae species captured with W.O.T. traps baited with rotting liver, from December 1993 to November 1994, at the Rio de Janeiro Zoological Garden.
Monthly frequency of Musca domestica, Synthesiomyia nudiseta, and Ophyra aenescens captured with W.O.T. traps from December 1993 to November 1994 with wind oriented traps, baited with decomposing beef liver in the Rio de Janeiro Zoo.