Improvement of Ips typographus catches in pheromone trap barriers by altering of sex assigned pheromone blends

The present study was based on the idea of a pheromone trap barrier with alternating dispensers releasing different pheromone mixtures that affect males and females differently. We tested the possibility of increasing the catch efficacy of pheromone trap barriers by altering the pheromone mixture with low levels of cis-Verbenol (cV, targeting males, BM), the mixture with high levels of cV (targeting females, BF) and the pheromone mixture with intermediate levels of cV (SL). In addition, we were interested in lowering the dispersion of attracted bark beetles, especially males, which reduces the risk of attack on trees in the surroundings. Significant highest absolute and relative catch was found in the catch of the combination BM–BF, which was 2.2-fold higher than the catch of the control barrier treated with commercial IT Ecolure baits (Fytofarm, Slovakia). At the same time, the lowest dispersal in the surroundings of the barrier with the combination BM–BF was found, which was 2.5-fold lower than in the control barrier. The performance of the BM–BF combination of mixtures was proved in a field trial experiment where the total season catch of the part of the barrier treated with BM–BF dispensers caught 1.5-fold more beetles during the season than the control part treated with IT Ecolure dispensers. Furthermore, the results confirm that the performance of the combination of low levels of cV (targeting males) and high levels of cV (targeting females) is complemented by the desired reduced dispersion around the barrier, which reduces the risk of attack on trees in the surroundings

Spruce Protection against <i>Ips typographus</i> with Anti-Attractant Blend of Tree-Based Semiochemicals: From Small Experimental Plots to Stand Scales

Tree-killing bark beetles require rapid management, such as anti-attractants, to stop the enlargement of attack hot-spots. We tested two newer anti-attractant blends, both without verbenone and one with the addition of trans-4-thujanol, in traps against standard pheromone baits for inhibition of catch. Both blends provided effective catch reduction (>95%). We also tested these anti-attractant blends in tree protection experiments for two years. We had experimental plots with a center of an anti-attractant protected tree zone, with no traditional control area, but we followed tree kills in 10 m wide concentric rings to 100 m. In 2020, we had 12 plots, and 9 plots in 2021. Monitoring by low-strength pheromone traps followed beetle flight averaging 300/trap during the shorter period, August 2020, and 5000/trap during the longer period, May to August 2021. The blends of anti-attractants were 100% effective in avoiding tree mortality in both treated trees and their surroundings. There were no bark beetle attacks on any treated trees, and there was zero tree mortality up to 19 m in 2020, and up to 30 m in 2021, thus full protection to circa 20 m. The density of killed trees then increased from close to zero, over 20 to 50 m, reaching a level of ca 30 (trees/ha) then declined. The spatial pattern of tree mortality on our experimental plots was highly heterogeneous and individual 10m-ring data points on tree kill density could not be statistically separated. In contrast, a non-linear regression model showed a continuous increase of attacks over the distance from the center to a peak ca 60m, followed by a decline. This model agrees partly with the only similar study in the literature, but importantly, it does not give a peak of kill density at distances between the first and second rings close to treatment zones. Such patterns of close-quarter kills have been observed as a “switching” of attack in this and other scolytid systems manipulated by anti-attractants, but not in the present study, likely due to the elimination of verbenone from our blends