CALLIPHORIDAE (DIPTERA) OF THE COASTLINE OF BUENOS AIRES, ARGENTINA: SPECIES COMPOSITION, NUMERICAL TRENDS, AND BAIT S PREFERENCES 1

Transcription

1 Volume 117, Number 2, March and April CALLIPHORIDAE (DIPTERA) OF THE COASTLINE OF BUENOS AIRES, ARGENTINA: SPECIES COMPOSITION, NUMERICAL TRENDS, AND BAIT S PREFERENCES 1 Pablo R. Mulieri, 2 Juan P. Torretta, 3 Juan A. Schnack, 4 and Juan C. Mariluis 5 ABSTRACT: The blow fly community was surveyed in the coastline of Río de la Plata at an ecological reserve in Buenos Aires city. Samples were taken monthly (September 2003 to August 2004). Dog faeces and rotten cow liver were used as baits and their attractiveness compared regarding overall number, species and sex preferences. Cochliomyia macellaria, Phaenicia cluvia, and Sarconesia chlorogaster were dominant. The remaining species recorded were scarcely represented (< 20 %). Number of specimens taken from faeces and liver did not show significant differences. Numerical trends were similar between both baits. Regarding species preference, C. macellaria was more abundant on faeces while S. chlorogaster preferred liver, while Phenicia cluvia did not show a definite trend. In total, females were more abundant than males. C. macellaria and P. cluvia s sex ratio was female biased; S. chlorogaster did not exhibit sexual asymmetries. A comment was given on the potential sanitary impact of the dominant species. KEY WORDS: Calliphoridae, species composition, Buenos Aires, Argentina, coastline, bait s preference, dog faeces, rotten cow liver Blow flies are among the most abundant exploiters of carcasses and faeces for food source, egg lying, and / or larval development (Hanski and Kuusela, 1980; Kuusela and Hanski, 1982; Martínez Sánchez et al., 2000). Due to their medical and veterinary importance as myiasis producers and vectors of pathogens (Greenberg, 1971, 1973), ecological studies on blow flies have been mainly focused on the association with human settlements. The degree of synanthropy would indicate the ability to colonize human settlements (Nuorteva, 1963). Classical works (Gregor and Povolny, 1958; Nuorteva, 1963) have distinguished three kinds of habitats, according to their decreasing degree of human influence: eusynanthropic, hemisynanthropic, and asynanthropic, respectively. In the Neotropics, ecological studies on calliphorid communities have been mostly conducted either at isolated dwellings or at dense urban settlement. Conversely, wild areas have been scarcely surveyed. The few available references on feeding preference of blow flies in wild areas are so far restricted to tropical areas of South America in Brazil (Linhares, 1981; d Almeida, 1994) and Perú (Baumgatner and Greenberg, 1985). 1 Received on June 27, Accepted on October 10, ANLIS Dr. Carlos Malbrán, Departamento de Vectores. Av Vélez Sarsfield 563 (1281), Buenos Aires, Argentina. mulierii@yahoo.com.ar. 3 Cátedra de Botánica Agrícola, Facultad de Agronomía, Universidad de Buenos Aires. Av. San Martín 4453 (1417) Buenos Aires, Argentina. torretta@agro.uba.ar. 4 Division Entomologia, Museo de La Plata, Universidad Nacional de La Plata, Paseo del Bosque s/n. (1900), La Plata, Argentina. js@netverk.com.ar. 5 ANLIS Dr. Carlos Malbrán, Departamento de Vectores. Av Vélez Sarsfield 563 (1281), Buenos Aires, Argentina. jcmariluis@yahoo.com.ar. Mailed on May 17, 2006

2 140 ENTOMOLOGICAL NEWS Fig. 1. Geographic location of the study site.

3 Volume 117, Number 2, March and April The aim of this study is to determine abundance, species richness and feeding preference of species of calliphorid housed by the Reserva Ecológica Costanera Sur (RECS) in the coastline of Río de la Plata, Buenos Aires. METHODS Study area The study site, which covers 343 ha, was declared a Natural Park and Ecological Reserve in Even though it is located at the eastern portion of Buenos Aires city (34º 37' S; 58º 21'W) (Fig. 1), the influence of urban activities is not highly remarkable. The site resembles a natural system: grasslands, shrubs and trees occupy terrestrial habitats while emergent and floating hydrophytes populate wetland of different sizes. Some of the latter ecosystems sustain large populations of the black-necked swan, Cygnus melancorhyphus and other waterfowl species (e.g. Anas spp., and Fulica sp.). Two hundred and fifty species of birds, 9 amphibians, 23 reptiles, 10 mammals, and 50 butterflies, and 245 plant species from 55 families have been recorded in this ecological reserve. Although the study site is an anthropogenic system, settled after the littoral portion of the Río de la Plata was refilled by materials extracted while a road construction took place during the 1970s, it has rapidly evolved toward quasi natural ecosystems. Part of these ecosystems constitute true wetlands whose importance relative to other biotopes has determined the recent inclusion of the RECS within the Ramsar List of Wetlands of International Importance (Ramsar site no. 1459, since March 22, 2005). The sampling spot is an embankment which surrounds intermittently flooded flatlands. This site receives direct sunlight and is dominated by the emergent marsh plant, Cortaderia selloana (Poaceae) and scattered grasses, trees, and shrubs (Fig. 2). Fig. 2. The sampling site at RECS.

4 142 ENTOMOLOGICAL NEWS Sampling Monthly samplings were undertaken from September 2003 to August Seven hourly captures of adult flies (10:00 am 4:00 pm) were taken with a hand net on two different kinds of baits exposed during 15 minutes each hourly capture. Therefore, the first sample took place from 10:00 am to am and the last one from 4:00 pm to 4:15 pm. The baits used were composed of 200 g of rotten cow liver, all of them five days aged at ambient temperature in order to allow their comparison and 200 g of fresh dog faeces. While the former bait increases its attractiveness to blow flies as time elapses (Fisher et al. 1998), dog faeces rapidly get dried while exposed to sunlight. The baits were always placed in the same place, 30 m apart from each other, and kept in closed containers recipients after each capture. Flies were killed in glass vials with carbon tetrachloride in the field, and identified and sexed in the laboratory. Identification was made following the keys of Mariluis and Schnack (2002). Data Analysis To compare fly abundance between bait types and to estimate deviations of an expected sex ratio 1:1, individual species abundance data were subjected to a chisquare test. Overall abundance of calliphorids on liver and on faeces was compared by means of a parametric t-test for dependent samples; therefore, each sampling date could be included into a single analysis. The same analysis was used to compare male versus female overall abundance. Data of each sampling date were examined for normality and log (n+1) transformation of fly number was performed as appropriate. The degree of association between overall numbers of flies captured on liver and on faeces was correlated by means of the Pearson coefficient. RESULTS During the sampled year, a total of 616 specimens were captured. Cochliomyia macellaria (Fabricius), Phaenicia cluvia (Walker), and Sarconesia chlorogaster (Wiedemann) were dominant. The remaining recorded species were Calliphora nigribasis Macquart, Calliphora vicina Robineau-Desvoidy, Chrysomya albiceps (Wiedemann), Chrysomya megacephala (Fabricius), Cochliomyia hominivorax (Coquerel), and Lucilia sericata (Meigen) (Table 1). Blow fly overall abundance recorded from faeces and liver did not show significant differences (t-test for dependent samples: t = 0.506; df = 11; p = 0.622) (Fig. 3). Moreover, numerical trends, exhibited significant correlations between both baits (r = 0.81; p < 0.05). However, at species level C. macellaria was more abundant on faeces while P. cluvia did not exhibit significant differences between both used baits. Sarconesia chlorogaster showed preference for liver (Table 1).

5 Volume 117, Number 2, March and April Fig. 3. Overall blow fly abundance captured with liver and faeces baits at RECS (September 2003-August 2004). Table 1. Overall abundance of Calliphoridae at RECS, Buenos Aires (September August 2004). Bait Species Faeces Liver χ 2 (df=1) P Cochliomyia macellaria (Fabricius) Phaenicia cluvia (Walker) Sarconesia chlorogaster (Wiedemann) Cochliomyia hominivorax (Coquerel) Callíphora vicina Robineau-Desvoidy Lucilia sericata (Meigen) Chrysomya albiceps (Wiedemann) Chrysomya megacephala (Fabricius) Callíphora nigribasis Macquart Total

6 144 ENTOMOLOGICAL NEWS Female overall abundance was higher than males on faeces (t-test for dependent samples: t = , df = 11, p = 0.044) and on liver (t-test for dependent samples: t = , df = 11, p < 0.001) (Fig. 4a, b). Fig. 4. Overall abundance of males and females of calliphorid captured with a) faeces and b) liver baits at RECS (September 2003-August 2004).

7 Volume 117, Number 2, March and April Sex ratio was female biased for C. macellaria (χ 2 = 40.67, df = 1, p < 0.001) and for P. cluvia (χ 2 = 56.99, df = 1, p < 0.001) but no differences from an equal sex representation were found for S. chlorogaster (χ 2 = 0.184; p = 0.668). The same trends were obtained for each separate bait analysis (Table 2). The number of females of C. macellaria did not show significant differences between the two baits (χ 2 = 2.21, df = 1, p = 0.073); nevertheless, males showed preference for faeces (χ 2 = 8.39, df = 1, p = 0.004). Females of P. cluvia were more abundant on liver (χ 2 = 8.26, df = 1, p = 0.004), while higher number of males were found on faeces (χ 2 = 7.41, df = 1, p = 0.006). Both sexes of S. chlorogaster showed quite similar patterns, but the low number of specimens obtained did not indicate a definite trend. Daily numerical changes in abundance were not taken into account because they were negligible. Also, null numbers were recorded for many daily samples. We could not detect a definitive trend of hourly variations in abundance. Table 2. Sex ratio of the most representative blow fly species captured from faeces and liver at RECS, Buenos Aires (September 2003-August 2004). Faeces Liver Species %% $$ χ 2 (df=1) P %% $$ χ 2 (df=1) P C. macellaria > >0.001 P. cluvia >0.001 S. chlorogaster DISCUSSION Whereas exotic and cosmopolitan blow fly species were poorly represented in the RECS, the three dominant species, which represented 97% of the total sample, were Neotropical. Among the latter, C. macellaria was the most abundant, totaling more than 50% of the whole sample. This species has been catalogued as dependent either on urban or on suburban settlements, while populations of the remaining Neotropical species recorded, P. cluvia and S. chlorogaster may inhabit wild habitats (Schnack et al., 1989, 1995) although the latter is reported as eusynanthropic in Brazil and Perú (Ferreira, 1978, Baugartner and Greenberg, 1985). The ecological role played by C. macellaria would suggest that the RECS is somehow affected by the neighboring urban environment.

8 146 ENTOMOLOGICAL NEWS The absence of Compsomiyops fulvicrura, Paralucilia pseudolyrcea, Phaenicia eximia, and Phaenicia cuprina during this survey is remarkable as they were previously included among the fourteen species recently recorded for the western coastline of Río de la Plata (Mariluis and Mulieri, 2003). In RECS, the exotic species C. albiceps, C. megacephala, and the cosmopolitans, C. vicina and L. sericata, frequently observed in urban settlements, were extremely scarce. The observed seasonal trends of overall number of captures suggest that blow fly activity is higher during fall and spring, suggesting therefore that adult species are sensitive and less tolerant to the high and low temperatures they are exposed to during summer and winter, respectively. The dominance of C. macellaria would be attributed, in addition to RECS closeness to urban settlements, to the fact that this species does not specifically interfere with the recently introduced species, C. albiceps. This Palaearctic species has been considered as responsible for the decline of C. macellaria populations in wide areas of South America (Guimarães et al., 1978; Baumgartner and Greenberg, 1984). Larvae of C. albiceps are facultative predators of Diptera larvae exploiting similar habitat and food. C. macellaria seems to be highly affected by this asymmetrical competition (Wells, 1992; Faria et al., 1999) which also may have negatively affected individuals of Phaenicia spp. (Madeira, 1985). Therefore, the low relative importance of C. albiceps in RECS may explain the high numerical representation of C. macellaria and P. cluvia. Although C. albiceps might also influence the decline of S. chlorogaster (Mariluis and Schnack, 1986), the scarcity of the latter has been observed in several locations of subtropical South America independently of the occurrence and abundance of C. albiceps (Ferreira, 1978; Schnack et al., 1995; Mariluis and Schnack, 1996). With regard to bait preference, previous studies have shown a stronger preference of adult blow flies for carrion than for faeces (Linhares, 1981; Baumgartner and Greenberg, 1985). The survey carried out in RECS shows that the overall number of flies obtained in both baits were similar. However, bait preferences differ between two of the dominant species. Although C. macellaria was dominant at both baits, it exhibited preferences for faeces, while S. chlorogaster was more abundant on liver. P. cluvia did not show a definite preference for either bait as it was formerly observed in the cogenerics P. eximia in Curitiba, Brazil (Ferreira, 1978). The preference for faeces exhibited by C. macellaria may suggest its expected population increase, not only in the RECS, but also in other areas nearby, inhabited by abandoned dogs as well as in locations of the city where dog s owners allow them to defecate in the streets or in recreational spaces, a behavior frequently observed, even in high class neighborhoods in downtown Buenos Aires. This has medical and veterinary importance in the dissemination of viruses, bacteria and parasites. Regarding adult females, while no differences were observed between the used baits for C. macellaria, P. cluvia females showed preference for liver. Males

9 Volume 117, Number 2, March and April of both species were more abundant on faeces than on liver. As Stoffolano et al. (1995) pointed out, for successful insemination of females mature eggs, males of some blow fly species need a source of protein, which may be eventually supplied by faeces. ACKNOWLEDGEMENTS We thank the staff of the Reserva Ecológica Costanera Sur located in Buenos Aires, Argentina, for hosting this study. We also thank the suggestions of two anonymous reviewers. V. H. Calvetti and N. Callegaris produced the Figure 1. This research was funded by the Technical and Scientific National Research Council of Argentina (CONICET). LITERATURE CITED Baumgartner, D. L. and B. Greenberg The genus Chrysomya (Diptera: Calliphoridae) in the New World. Journal of Medical Entomology 21: Baumgartner, D. L. and B. Greenberg Distribution and medical ecology of the blow flies (Diptera: Calliphoridae) of Peru. Annals of the Entomological Society of America 78: d Almeida, J. M Ovipositional substrates used by calyptrate Diptera in Tijuca Forest, Rio de Janeiro. Memorias do Instituto Oswaldo Cruz 89 (2): Faria, L. D. B., R. Orsi, L. A. Trinca, and W. A. C. Godoy Larval predation by Chrysomya albiceps on Cochliomyia macellaria, Chrysomya megacephala, and Chrysomya putoria. Entomologia Experimentalis et Applicata 90: Ferreira, M. J Sinantropia de dípteros muscóideos de Curitiba, Paraná. I: Calliphoridae. Revista Brasileira de Biología. 38 (2): Fisher, P., R. L. Wall, and J. R. Ashworth Attraction of sheep blowfly L. sericata to carrion bait in the field. Bulletin of Entomological Research 88: Greenberg, B Flies and Disease, Volume 1. Princeton University Press. Princeton, New Jersey, U.S.A. 856 pp. Greenberg, B Flies and Disease, Volume 2. Princeton University Press. Princeton, New Jersey, U.S.A. 447 pp. Gregor, F. and D. Povolny Versuch einer Klassifikation der Synanthropen Fliegen. Journal of Hygiene, Epidemiology, Microbiology and Immunology 2: Guimarães, J. H., A. P. Prado, and A. X. Linhares Three newly introduced blow fly species in Southern Brazil (Diptera: Calliphoridae). Revista Brasileira de Entomología. 22: Hanski, I. and S. Kuusela The structure of carrion fly communities: differences in breeding seasons. Annales Zoologici Fennici. 17: Kuusela, S. and I. Hanski The structure of carrion fly communities: the size and type of carrion. Holarctic Ecology 5: Linhares, A. X Synanthropy of the Calliphoridae and Sarcophagidae (Diptera) in the city of Campinas, São Paulo, Brazil. Revista Brasileira de Entomología 25 (3): Madeira, N. G Hábito de pupação de Calliphoridae (Diptera) na naturaleza e o encontro do parasitóide Spalangia endius (Hymenoptera: Pteromalidae). Revista Brasileira de Zoología 45 (4):

10 148 ENTOMOLOGICAL NEWS Mariluis. J. C. and P. R. Mulieri The distribution of the Calliphoridae in Argentina (Diptera). Revista de la Sociedad Entomológica Argentina 62 (1-2): Mariluis, J. C. and J. Schnack Ecología de una taxocenosis de Calliphoridae del área platense (Provincia de Buenos Aires) (Insecta, Diptera). Ecosur 12/13 (23/24): Mariluis, J. C. and A. Schnack Elenco específico y aspectos ecológicos de Calliphoridae (Insecta, Diptera) de San Carlos de Bariloche, Argentina. Boletín de la Real Sociedad Española de Historia Natural (Sección Biológica) 92 (1-4): Mariluis, J. C. and J. Schnack Calliphoridae de la Argentina. Sistemática, ecología e importancia sanitaria (Diptera, Insecta), pp In, Salomón, O. S. (Editor). Actualizaciones en Artropodología Sanitaria Argentina. Buenos Aires, Argentina. 302 pp. Martínez Sánchez, A., S. Rojo, and M. A. Marcos García Annual and spatial activity of dung flies and carrion in a Mediterranean holm-oak pasture ecosystem. Medical and Veterinary Entomology 14: Nuorteva, P Synanthropy of Blow flies (Dipt., Calliphoridae) in Finland. Annales Entomologici Fennici 29: Schnack, J. A., J. C. Mariluis, J. Muzón, and G. R. Spinelli Synanthropy of Calliphoridae. A first approach in Argentina (Insecta, Diptera). Eos 62 (2): Schnack, J. A., J. C. Mariluis, N. Centeno, and J. Muzón Composición específica, ecología y sinantropía de Calliphoridae (Insecta: Diptera) en el Gran Buenos Aires. Revista de la Sociedad Entomológica Argentina 54 (1-4): Stoffolano, J. G., Jr., M. F. Li, J. A. Sutton, and C.-M. Yin Faeces feeding by adult Phormia regina (Diptera: Calliphoridae). Medical and Veterinary Entomology 9: Wells, J. D Chrysomya rufifacies (Macquart): an Introduced Blow Fly and its Effects on the Native cochliomyia macellaria. Ph. D. Dissertation. University of Illinois at Chicago, Illinois, U.S.A. 101 pp.