The Population Ecology of Muscina Stabulans (Fallén) (Diptera: Muscidae), Along an Urban-Rural Gradient of Buenos Aires, Argentina
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May - June 2010 441 PUBLIC HEALTH The Population Ecology of Muscina stabulans (Fallén) (Diptera: Muscidae), along an Urban-Rural Gradient of Buenos Aires, Argentina LUCIANO D PATITUCCI1,2, PABLO R MULIERI1,2, JUAN C MARILUIS1,2, JUAN A SCHNACK1,3 1Consejo Nacional de Investigaciones Científi cas y Técnicas, Buenos Aires, Argentina 2ANLIS “Dr C Malbrán”, Depto Vectores, Av Vélez Sarsfi eld 563, CP 1281, Buenos Aires, Argentina; [email protected]; [email protected]; [email protected]; [email protected] 3División Entomología, Facultad de Ciencias Naturales y Museo, Univ Nacional de La Plata, Paseo del bosque s/n, CP 1900 La Plata, Buenos Aires, Argentina; [email protected] Edited by Álvaro Eiras – UFMG Neotropical Entomology 39(3):441-446 (2010) ABSTRACT - The false stable fl y, Muscina stabulans (Fallén), was surveyed along an urban-rural gradient at Almirante Brown, Buenos Aires province, Argentina. Samples were taken at monthly intervals from May 2005 to April 2007. Hourly captures of adult fl ies (10:00 am – 04:00 pm) were taken at each sampling date with a hand net. The baits used were 250 g of rotten cow liver and 250 g of fresh dog faeces exposed in shaded and sunny areas. The entire sample accumulated 358 specimens. The number of specimens captured during the second year was higher than in the fi rst year. Muscina stabulans was more abundant at urban-suburban sites. Females showed signifi cant preferences for cow liver. We caught more specimens in shaded areas. The hourly activity increased toward the afternoon at the three sites. The present work was the fi rst ecological study related to a muscid species in Argentina. KEY WORDS: False stable fl y, bait preference, heliophily, urbanization The physical changes along the urban-rural gradient (Laos et al 2004). Recent fi ndings revealed its importance in including increase in human density, urbanization, pollution, the fi eld of forensic entomology (Oliva 2007). and other perturbations attributed to human intervention on Flies contact with food incorporates additional risks by environment produce natural habitat loss (McKinney 2002). mechanical transport of food borne pathogens (Greenberg These changes promote an increase in environmental aridity, 1971). Each female may lay from ca. 140 to 200 eggs, over air turbidity, and heat production, all of which make cities the food it spends. Larvae exploit temporarily irregular and warmer than rural and wild environments (Gottschalk et al ephemeral resources (James 1947) and their development 2007). The disturbed habitat at the urban core provides new time is directly correlated to ambient temperature (Mascarini opportunities for non-native species because they can utilize & Prado 2002). Their role as producers of traumatic miasis new and different resources. These species well adapted in animals (James 1947) and gastrointestinal diseases have to altered environments are frequently regarded as “urban concerned regulatory agencies of sanitation and public health exploiters” (McKinney 2002). (Graczyk et al 2005). A few records of intestinal (DeFoliart Muscina stabulans (Fallén), the false stable fl y, is a & Pelton 1955) and cutaneous myiasis have been recorded cosmopolitan species, very common in the Neotropics for this species (James 1947). (Carvalho & Couri 2002, Carvalho et al 2005). In Argentina, Synanthropic studies of Muscidae in the Neotropical its geographical range includes Salta, Buenos Aires, Tucumán region have examined the relationship between M. stabulans (Shannon & Del Ponte 1926) and Río Negro (Malloch and the urban environments (Linhares 1981, Carvalho et 1934) provinces. This species often inhabits fi lthy habitats, al 1984, Figueroa-Roa & Linhares 2004). In Argentina, including latrines, and household wastes, as well as with comparative studies of calyptrate fl ies in several geographical habitats created by agriculture (Queiroz & Carvalho 1987) locations have been undertaken only for calliphorids and and other human activities like live stock manure and sarcophagids (Schnack & Mariluis 2004, Mariluis et al wastewater treatment plants (Laos et al 2004). Some reports 2007). have determined the negative economic impact of this fl y on We expected to fi nd higher number of false stable fl ies at dairy farms and on poultry industries (Perotti & Brasesco urban site compared to suburban and rural site. The aim of 1996, Avancini & Silveira 2000). In Argentina, the false this work was to analyze different attributes of M. stabulans, stable fl y has been found in poultry farms in southeast Buenos like sex ratio, synanthropy, seasonal and daily numerical Aires province (Perotti & Brasesco 1996), and has been changes, bait preference, and heliophily, comparing them associated to composting of biosolids in Rio Negro province along an urban-rural gradient at locations of Almirante 442 Patitucci et al - The Population Ecology of Muscina stabulans (Fallén) (Diptera: Muscidae), along an... Brown, Buenos Aires province. Furthermore, we aspire that Rivadavia where native vegetation remained, adjacent to our study might be of value to assess the economical and compounds dedicated to cattle rising; the place was not sanitary potential impacts of this species within the area of infl uenced by dwellings, roads and other constructions. infl uence of the study sites. Vegetation of the rural site included native species of grasslands, herbs, shrubs, and trees (e.g., Eryngium spp., Baccharis spp., Celtis tala, Parkinsonia aculeata and Citrus Material and Methods trifoliata). The climate was temperate and humid, as it is expected Study areas. The study was carried out in Almirante Brown for the plains in median latitude. We measured temperature district, ca. 20 km south of Buenos Aires city and covered and relative humidity in each site and sampling date along three sampling environments: a densely populated urban, the two years surveyed (Fig 1). a place housing isolate dwellings, and a rural. The urban site (34º 50’ 15.02’’ S – 58º 23’ 52.75’’ W) was placed in Field samples. Muscids are small and very mobile organisms, the commercial and residential building of the central area diffi cult to sample randomly. Thus sampling methods are of the locality of Burzaco. The suburban site (34º 49’ 36.9’’ mostly based on estimates or counts on aggregation sites, such S – 58º 24’ 16.56’’ W) was placed in a sector that housed as fl y attracting baits (Muirhead-Thomson 1968). Samples scattered country residences with widespread buildings were taken from May 2005 to April 2007 once a month per surrounded by large grasslands, gardens, woodlands, and site. Every sampling date, seven hourly captures of adult fl ies streets without pavement. The rural site (34º 51’ 29.38’’ S (10:00 am - 4:00 pm) were collected with a hand net. Two – 58º 23’ 17.75’’ W) was placed in the locality of Ministro kinds of baits were used: 250 g of rotten cow liver (fi ve days 35 30 25 20 15 Temperature (º C) Temperature 10 5 0 100 90 80 70 60 50 40 30 Relative humidity (%) 20 10 Urban Suburban Rural 0 Jul-05 Jul-06 Jan-06 Jan-07 Jun-05 Jun-06 Oct-05 Oct-06 Sep-05 Sep-06 Feb-06 Feb-07 Apr-06 Apr-07 Dec-05 Dec-06 Mar-06 Mar-07 Aug-05 Aug-06 Nov-05 Nov-06 May-05 May-06 Months Fig 1 Monthly temperature and relative humidity of a rural, suburban and urban area during ecological study of Muscina stabulans (dots represent daily mean value) in Almirante Brown, Buenos Aires province. May - June 2010 Neotropical Entomology 39(3) 443 aged) and 250 g of dog faeces. The baits were exposed in Results shaded and in sunny areas for 15 min at each hourly capture. The sampling effort was the same at each site and consisted During the two years sampled, a total of 358 specimens of four baits per site, two in the shade and two in the sun (one were collected at the three studied sites. Muscina stabulans of rotten cow liver and one of dog faeces, in the shade and in occurred in all samples during both years. During the the sun, respectively). fi rst year (May 2005-April 2006) this species showed the Specimens were killed in glass vials with carbon highest number in the summer and in early autumn, whereas tetrachloride and were stored in the field as described during the second year (May 2006-April 2007) the highest elsewhere (Schnack & Mariluis 2004); once in the laboratory, abundance was observed in spring and in early summer (Fig they were identifi ed using the key of Carvalho & Couri 2). The number of specimens captured during the second (2002). year was higher than in the fi rst year, but the difference was The Wilcoxon’s test was used to compare the abundance marginally signifi cant (Wilcoxon test T = 14; P = 0.049). The between the two years. The association of the fl y abundance correlations between abundance of fl ies captured and relative with relative humidity and mean temperature at each site humidity and temperature were not signifi cant at urban (Tº: was correlated by means of the Spearman rank correlations r = 0.097, P > 0.01; RH: r = -0.467, P > 0.01), suburban (Tº: (Zar 1996). r = 0.468, P > 0.01; RH: r = -0.176, P > 0.01) and rural sites The degree of species synanthropy was measured by (Tº: r = 0.386, P > 0.01; RH: r = -0.420, P > 0.01). two different methods. We calculated total frequencies per According to Nuorteva index, M. stabulans behaved as site to obtain the synanthropic index (S.I.) (Nuorteva 1963). a synanthropic species (S.I. = + 68.02). While differences This index was compared with the Chi-square analysis. were not remarkable between baits, overall number of fl ies On the other hand, a Friedman’s test of variance by ranks captured showed signifi cant differences among the studied was applied to the number of fl ies per sample, by using the sites (χ2 = 131.91 d.f.