Browsing by Subject "vuokapyydys"

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  • Thomssen, Pia-Maria (Helsingfors universitet, 2012)
    Old hollow trees are an important habitat for many saproxylic species. A number of threatened and rare insects are specialized on tree hollows and live in the walls of cavities or in the loose wood mould accumulating in the bottom of the hollow. In this study, I compared the species richness and composition of Coleoptera in hollow trees caught with three trap types, window, aluminium foil and pitfall traps. Furthermore, I compared the time spent handling each sample of the different trap types, when sorting all insect orders (including Coleoptera) from the material. The material was gathered in parks and mansion areas in the Helsinki metropolitan area. Window, foil and pitfall traps were placed inside cavities of Tilia cordata, Acer platanoides and Quercus robur trees. In each tree two of each trap type was placed, i.e. six traps per tree, making a total of 90 traps. The traps were emptied every third week during May to July 2006. When the samples were sorted for the first time to separate different insect orders, the duration of time spent sorting each sample was documented. A total of 3825 Coleoptera individuals from 212 species were caught, of which 3398 individuals from 121 species were saproxylic. Window traps caught 1639 individuals from 140 species, foil traps caught 1506 individuals from 134 species, and pitfall traps caught 680 individuals from 111 species. The time spent sorting each sample was on the average shortest with pitfall traps and longest with aluminium foil traps. The ?-diversity (species composition and abundance) differed between the three trap types. The ?-diversity between window and foil, window and pitfall, and foil and pitfall traps was 37%, 13% and 14% respectively. In addition for the average number of saproxylic beetle species and individuals, the average time spent sorting each sample differed statistically significantly between window and pitfall traps (p<0,05), and foil and pitfall traps (p<0,05). Window and foil traps caught, on the average, clearly more saproxylic species and individuals as compared with pitfall traps. Pitfall traps also caught, on the average, less saproxylic beetles out of total beetle individuals (59%) than window (69%) and foil traps (71%). Window traps were the most efficient conserning the average number of saproxylic beetle individuals in relation to the average time spent sorting each sample. Efficiency value (individuals/minute) for each trap type was 0,74 for window, 0,43 for aluminum foil and 0,21 for pitfall traps. Window traps have never before been used inside tree hollows, they have only been used to collect insects outside the cavities. However they functioned outstandingly inside the cavities. In this study pitfall traps were clearly outperformed by window and foil traps, still many species, even some threatened ones, would have been lost without them. To achieve as diverse a species composition as possible it is recommended to use either window or foil traps parallel with pitfall traps.