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ŠUMARSKI LIST 9-10/2016 str. 57     <-- 57 -->        PDF

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Efficiency of dry and wet flight barrier Theysohn® pheromone traps in catching the spruce bark beetles Ips typographus L. and Pityogenes chalcographus L.
Eight toothed spruce bark beetle (Ips typographus L.) and six toothed spruce bark beetle (Pityogenes chalcographus L.) are most imported pests of mature spruce forests in whole Europe. When the populations are low they usually attack the trees which are weakened by snow, wind, highlight or some other biotic or abiotic factors. When the populations increase higher they can attack and kill living standing trees and-thus become primary pests. Monitoring of populations with pheromone traps is an important tool in integrated forests protection. During the last two decades the foresters in Croatia mainly use the classic black Theysohn® flight barrier pheromone traps for monitoring of spruce bark beetle populations in spruce forests.
The aim of the study was to investigate is there any significant difference in catches between dry and wet flight barrier pheromone traps, is there any possibility that bark beetles can escape from pheromone traps after they fall down in plastic box at the bottom of pheromone traps, and is there any difference in selectivity of compared traps to predator species (Thanasimus formicarius L., Nemozoma elongatum L.).
In 2014. a field experiment was set up in spruce stands in two sites, one in higher elevation and one in lower elevation. In each site three black Theysohn® flight barrier pheromone traps using water in collecting box were compared with three traps with dry boxes, for each bark beetle species. The holes on the bottom of collecting boxes on wet traps were sealed with silicone. Also new made holes at the side of collecting boxes were covered with plastic net to stop the loss of captured bark beetles with water overflow. The traps were loaded with pheromone lures – Pheroprax® lure for I. typographus and Chalcoprax® for P. chalcographus.
Totally for each species were set up six pairs of dry-wet pheromone traps, three pairs on lower and three pairs on higher elevation.
The experiment started 17th of May and was finalized in the last week of September. The traps were emptied every eight days. The caught beetles were kept in 60% ethanol until the moment when they were determined and counted. Except the two main bark beetle species, also the predator species T. formicarius and N. elongatum were counted. In total 73.994 specimens of I. typographus were caught in dry, and 71.212 specimens in wet traps. In dry traps 214.950 specimens of P. chalcographus were caught, and 179.146 specimens in wet traps. There was no significant difference between dry and wet pheromone traps for both bark beetle species. It can be concluded easily that I. typographus and P. chalcographus could not escape from traps after they fall down in collecting box at the bottom of traps, what isn’t case with Tomicus species (Hrašovec & Pernek, unpublished results).
In both case bigger number of bark beetles (no statistically significant) were caught in dry traps. The reason may be the production of 1-hexanol and verbenon in wet traps. More dead bark beetles was found in wet pheromone traps what is logical because after they fall down in plastic hunting box which is full of water they get drown after some time, what is no case with bark beetles in dry pheromone traps. Increasing the number of dead beetles can reduce the efficiency of pheromone traps (Kretschmer, 1990; Bakke et al, 1983). The smell of dead bark beetles significantly reduce the efficiency of pheromone traps, but in the moment it wasn’t known which component were responsible for it. Lower efficiency of pheromone traps is consequence of production 1-hexanol and verbenon from dead bark beetles (Zhang et al., 2003).
Pernek (2006), Pernek & Lacković (2011) had a better monitoring results of silver fir bark beetle species (genus Pityokteines) with wet traps compared to dry traps. The classic black Theysohn® traps were used like in this experiment. The reason why the wet pheromone traps had shown a better results in previous research (Pernek, 2006; Pernek & Lacković, 2011) probably is consequence of different factors: biology and pheromone communication, swarming time, weather conditions and different type of stands. All this factor could have a important impact on pheromone trap catches.