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Discussion
This study showed that the prevalence of this parasite in its intermediate dung beetle hosts differs significantly among rural (2.3%), urban (13.5%) and peri-urban (0%) areas in the Tshwane (Pretoria) Metropolitan.Conditions for maximum dung beetle activity were sub-optimal during October 2006 when sampling took place.
Although temperatures were constantly above 25°C, no rain had yet been recorded for any of the localities in the rural, urban or peri-urban areas. The rural area was devoted to mainly small scale livestock and crop production, however, sampling sites were always located in patches of natural vegetation, which might explain why the highest number of species (11 species) was collected in that area. Although the peri-urban area had the second highest number of recorded species (nine species), sites in this area were heavily polluted by rubbish such as plastic bags, broken glass, paper and biological waste material. Furthermore, these sites were mostly ecologically degraded and the vegetation predominantly alien. The fact that the periurban sites had the second highest number of species might be attributable to the ever-present and seemingly abundant goats and cattle which roam the area. The urban area had the lowest species number (six) of all three the areas. Although the majority of gardens in this area are watered throughout the year, they represent a modified environment of which the vegetation is almost exclusively alien. A small patch of natural vegetation was found in only one of the urban sites, where a few ostriches were kept. Pesticides are also often applied to maintain the integrity and aesthetic value of gardens. In this study only omnivore dung specific dung beetles were found to be parasitized by Spirocerca lupi larvae. This might be related to the fact that the definitive hosts are mainly domestic dogs and a few other members of the family Canidae. There was a high concentration of domestic dogs in the urban area and the sampling sites in the rural area were all close to pig farms. Furthermore, owners of properties in the rural area often kept more than three dogs. A sufficient explanation cannot be offered for the absence of herbivore dung specific or generalist dung beetles from the peri-urban area.
Description of the study area
This study was conducted in Grahamstown, in the Eastern Cape Province of South Africa (33°18’S, 26°32’E) on the basis of being a focal area of high infection with S. lupi in dogs. Information on incidence of infection in dogs was obtained from ClinVet International Research Organisation, South Africa. The study area was classified into two main regions: a high human density region and a low human density region, based on characteristics of their respective land use, the number of people that resided in each of the two regions, and the potential free-range limits of dogs. The high human density region comprised of informal settlements and the general landscape was severely transformed by human activity. Flora consisted of mostly non-woody exotics; large areas were devoid of any vegetation with signs of advanced erosion damage. These areas were heavily polluted with household refuse and a noticeable feature of the landscape was the large amount of exposed faeces (predominantly human, dog, cattle and donkey). Dogs that frequented in this region were mostly feral. The low human density region was situated within the suburban zone of Grahamstown. This region consisted of well watered gardens, public open spaces in the form of parks and sports fields, and natural or semi-natural green spaces. Open green spaces comprised principally of natural indigenous vegetation of the Grahamstown Grassland Thicket vegetation type (McConnachie et al. 2008).
Sampling design
Dung beetles were sampled over one breeding season on three separate occasions: December 2007, February 2008, and April 2008, which coincides with high dung beetle activity (Davis 2002) in summer rainfall areas of South Africa. Sampling was conducted in four sites in the high human density region and in five sites in the low human density region. Collecting sites in the high human density region were selected on the basis of being frequented by high densities of feral dogs. The selection of specific sites for trapping in the low density region was based on information obtained from a local veterinarian on patient records pertaining to dogs that were infected by S. lupi and consultation with dog owners on where dogs had been taken for daily exercise. Exactly the same locations and pitfall trap positions were used for all three sampling occasions.
Pig dung-baited pitfall traps were used for sampling dung beetles. In this study the domestic dog was treated as an omnivore (see Chapter 1). Pig dung served as a surrogate for dog dung, because it is also an omnivore and strong smelling, and due to difficulties in procuring enough dog dung for baiting purposes. Pig dung used for bait was collected from a piggery to the east of Pretoria. Five pitfall traps were placed at 10 m intervals along a single transect line in sunny situations. Plastic buckets were used as pitfall traps and had a 1 L capacity (11 cm in diameter and 12 cm deep) and were sunk into the ground so that the rims of the buckets were level with the soil surface. They were filled to about one third of their volume with a water and soap solution to immobilise trapped beetles. On each trapping occasion the 0.5 L dung baits were suspended on u-shaped metal wire supports, which were placed over the buckets at ground level. Baits were wrapped in chiffon to allow for the diffusion of volatile compounds but at the same time exclude beetles from the dung baits.
Trap contents were collected 48 h after traps had been set and only scarabaeine dung beetles were collected from the traps. Species-level identification of dung beetles were carried out in the laboratory and conspecifics collected from the same locality in each of the two regions were pooled and stored together in absolute ethanol in labelled jars. Voucher specimens were deposited at the University of Pretoria Insect Collection.
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