Use of pheromone traps for monitoring fir bark beetles (Pityokteines spp.)

A decline of Silver fir (Abies alba) forests linked with an outbreak of fir bark beetles (Pityokteines spp) has been recently registered in Croatia. Pheromone traps baited with pheromone mixtures Curviwit® and Spiniwit®, were used for monitoring the presence of Pityokteines curvidens and P. spinidens. Traps were placed for the first time in 2004 in Litoric (Gorski Kotar- middle Croatia) and were used every year through 2011. The aim of this work was to determine what impact bark beetles have on the decline of Silver fir. The results during the eight year monitoring period show a clearly visible connection between fir bark beetles and fir decline. The largest catches in pheromone traps were measured between 2005 and 2007, which also coincides when the most injured trees were felled in the forests. Approximately 94% of the catches occurred in April and May, which implies that traps should be placed only in these months and thus lower monitoring costs. In 2007, the effectiveness of different trap systems was also tested. The commonly used Theysohn® trap with a dry container was modified by sealing the container so that added liquid could not efflux. The test results of dry versus wet traps indicate that higher numbers of beetles are caught in Theysohn® modified wet traps. Because standard protection measures in an outbreak situation usually produce poor results, the use of pheromone traps for monitoring fir bark beetles should be considered as one action for effective preventive and sanitary measures in protection of Silver fir.