Parasitol Res (2014) 113:4659–4662 DOI 10.1007/s00436-014-4182-4
Culicoides biting midge density in relation to the position and substrate temperature in a cattle dung heap Renke Lühken & Ellen Kiel & Sonja Steinke
Received: 16 September 2014 / Accepted: 10 October 2014 / Published online: 24 October 2014 # Springer-Verlag Berlin Heidelberg 2014
Abstract Dung heaps offer warm breeding sites, which might be suitable for a continuing development or even emergence at low air temperatures in winter. Therefore, this study collected substrate samples from the outer surface and core of a cattle dung heap at the beginning of the winter period. We aimed to analyze the density of immature Culicoides in relation to substrate position and temperature. We took samples from the outer layer and core of the dung heap at different heights. Floatation was used to extract Culicoides larvae from the dung heap samples. In order to rear larvae individually, we separated them in glass tubes. A total of 229 Culicoides larvae were extracted from the dung heap samples. Highest densities (99.1 % of all larvae) were recorded for the outer layers of the dung heap but hardly any in the core (0.9 % of all individuals). While the density of larvae was negatively correlated with increasing substrate temperatures, Culicoides larvae were found in a temperature range between 7.9 and 38.0 °C (mean 16.6 °C). Extracted larvae were reared to adults. All male individuals were identified as Culicoides obsoletus (Meigen), 1818 and all female individuals as C. obsoletus/Culicoides scoticus. It can be concluded that dung heaps offer temperature conditions, which allow the survival and probably also the development to adults for immature Culicoides also under harsh climate conditions in winter.
Keywords Ceratopogonidae . Culicoides obsoletus . Dung heap . Temperature R. Lühken (*) : E. Kiel : S. Steinke Research Group Aquatic Ecology and Nature Conservation, Department of Biology and Environmental Sciences, Carl von Ossietzky University of Oldenburg, Ammerländer Heerstraße 114-118, 26111 Oldenburg, Germany e-mail: [email protected]
Short communication The Bluetongue virus emerged in Europe since the late 1990s, transmitted by several species of biting midges (Diptera: Ceratopogonidae) of the genus Culicoides (Mehlhorn et al. 2009; Wilson and Mellor 2009). Moreover, biting midges were also involved in the transmission of the spread of the Schmallenberg virus since 2011 (De Regge et al. 2012; Rasmussen et al. 2012). Both viral diseases resulted in huge economic costs worldwide (Bath 1989; Velthuis et al. 2010; Conraths et al. 2012). At least in Northern Europe, biting midges need an overwintering strategy to resist harsh climate conditions with low winter temperatures. Although not studied in detail, Culicoides species in temperate climate zones are expected to hibernate in a late larval stage (Szadziewsi et al. 1997). Moreover, vector surveillance studies in Northern Europe indicated very low but regular activity of adult Culicoides also in winter (Losson et al. 2007; Bauer et al. 2009; Clausen et al. 2009; Hoffmann et al. 2009; Kiel et al. 2009; Mehlhorn et al. 2009). These findings raised a discussion whether or not these individuals represent an overwintering adult population or newly emerged imagines (Losson et al. 2007). The hibernation strategy of biting midges is probably an important factor influencing the overwintering of the Bluetongue virus or Schmallenberg virus (Koenraadt et al. 2014), which is still an unsolved riddle. Hörbrand and Geier (2009) hypothesized a positive correlation between the number of Culicoides in light-trap samples and the distance of the trap to dung heaps. A study carried out on different farm sites in the UK highlighted that cattle dung heaps are colonized by large numbers of overwintering immature biting midges, which were predominantly colonized by overwintering Culicoides obsoletus (Harrup et al. 2013). Dung heaps offer warm breeding sites (Husted 1994), which might be suitable for a continuing development or even
Parasitol Res (2014) 113:4659–4662
Fig. 1 a Schematic diagram of peripheral sampling of dung heap at 26 spots on horizontal layers (top=∼3.00–3.30 m, upper layer=∼2.00–2.75 m, medium layer=∼1.00–1.75 m, lower layer=0–0.75 m). b Schematic diagram of core sampling of dung heap at 22 spots, which were randomly chosen on three vertical core layers (V1–V3)
emergence at low air temperatures in winter. Thus, for example, Harrup et al. (2014) hypothesized that the first Culicoides emerging in the year originate from dung heaps in which immature stages develop faster. Depending on the amount of decaying organic material, it seems reasonable that the temperature differs within a dung heap. However, a study focusing on the link between the colonization densities of immature Culicoides, the position in a dung heap, and the temperature pattern within a dung heap was not conducted previously. Such knowledge might bring us closer to an understanding of the overwintering ecology of biting midges. We thus evaluated the density of immature Culicoides in response to the substrate temperature within a dung heap in Northern Europe at the beginning of the winter period. This study was performed at the end of October 2008 on a cattle farm in the marshland region of Northwest Germany. The week before, frosty weather had just started and air temperatures at night were below 0 °C. Livestock on this farm comprises about 250 cattle, and the dung heap was located 3– 10 m from two cattle stables. The dung had been piled during the last 6 months to a height of approximately 3.30 m and a circumference of 42 m (measured at 1.70 m height). Its outer shape was a broad-based flat pyramid. At first, we took samples from the outer layer of the dung heap, i.e., surface of the dung heap, at different heights: upper layer ∼2.00–2.75 m, medium layer ∼1.00–1.75 m, and lower layer 0–0.75 m (Fig. 1). From each layer, we took six samples. Additionally, four samples were taken from the top of the dung heap (top ∼3.00–3.30 m). Afterwards, we took samples from the core of the dung heap. To do so, we stepwise trenched the core of the dung heap in three vertical layers (V1–V3; Fig. 1). Each layer was sampled at eight random positions each. Before substrate sampling, we recorded the substrate temperature at every position with a penetration substrate thermometer (PCE-EN 882 Environment Meter, PCE Group, Meschede, Germany).
All samples were taken with a stainless steal grab sampling device. This grab covered a surface area of 15 cm×11 cm and sampled a total volume of 456 ml down to a maximal depth of 7.8 cm. Each sample was stored in 250-ml freezer bag (Ziploc-Tüten, Toppits, Minden, Germany) and transported to the laboratory. Wet weight of each sample was measured with a laboratory scale (Sartorius, LE4202S). Culicoides larvae were extracted from these samples via a floating method (see Steinke et al. (2014) for methodological details). In order to rear larvae individually, we separated them in 48-ml glass tubes with 8 cm in height and 3 cm in width, which were covered with a cotton gauze. As a reservoir for moisture, the bottom of each tube was grouted with gypsum (approximately 0.5–1.0 cm in height). The gypsum was mixed with some charcoal to prevent massive growth of bacteria and fungi. A total of 229 Culicoides larvae were transferred individually on a teaspoon of dung (5–10 g), which had been
Fig. 2 Immature Culicoides densities per kilogram recorded in the outer layer of a dung heap in response to sampling spot temperatures. Further differentiated according to the four horizontal layers: top (N=4), upper layer (N=6), medium layer (N=6), and lower layer (N=6)
Parasitol Res (2014) 113:4659–4662
carefully floated and sieved previously to exclude invertebrates from the rearing device. For both rearing experiments, the temperature was adjusted to a mean of 21.5±2.0 °C. All samples were regularly wetted with tap water and controlled for adult Culicoides every 2–4 days for the following 4 months. Emerged adults were preserved in 70 % ethanol. Colonization densities (number of Culicoides larvae per kilogram substrate) were calculated for each sample. Culicoides were identified according to morphological characters (Campbell and Pelham-Clinton 1960). Data analyses were done with the program R (R Core Team 2013) with the package ggplot2 (Wickham 2009) for the graph. A total of 229 Culicoides larvae were extracted from the dung heap samples. Of all Culicoides larvae (227 individuals), 99.1 % were found in samples from the outer layer (Fig. 2). Only 2 larvae (0.9 % of all individuals) were extracted from the core material. Most larvae in the outer layer were sampled from the lower layer (204 individuals, 89.1 % of all individuals; Fig. 2), i.e., the bottom layer of the dung heap. Much lower numbers were present in samples from the medium layer (23 larvae, 10.0 % of all individuals), and no larvae were found in the upper layer and the top layer. The number of Culicoides larvae per kilogram differed significantly between the horizontal layers (Kruskal-Wallis test, P