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Optimizing the attractiveness of pheromone baits used for trapping the four-eyed spruce bark beetle Polygraphus poligraphus

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Author list: Rahmani, Rizan;Viklund, Lina
Publication year: 2019
Start page: 721
End page: 730
Number of pages: 10
ISSN: 0931-2048
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Abstract
Bark beetles have caused extensive damage to forests in central Sweden during the past decade, and the four-eyed spruce bark beetle, Polygraphus poligraphus, seems to be involved. However, its role in these bark beetle outbreaks is still not clear. The purpose of this study was to develop an efficient pheromone bait for P. poligraphus, which would make it possible to study the species more carefully and thereby contribute to protect exposed forests in an environmentally friendly way. Three field studies were conducted in 2015, 2016 and 2018 in Medelpad, county of Västernorrland, Sweden. The pheromone of P. poligraphus, (-)-terpinen-4-ol, was tested at different release rates and in different enantiomeric purities, to find the most attractive formulation for the beetles. It was also tested in combination with racemic frontalin, a compound which has previously been shown to produce a synergistic effect together with (-)-terpinen-4-ol of low enantiomeric purity; 52% ee. Other compounds, chosen based on responses from electroantennographic studies, were also tested in an attempt to find additional attractants and repellents for P. poligraphus. The most attractive treatment tested was enantiomerically pure (-)-terpinen-4-ol (99% ee). When the enantiomeric purity was lower (50% ee), the trap catches was lowered to levels comparable to the catches for unbaited control traps. A strong synergistic effect with frontalin was observed for (-)-terpinen-4-ol of low enantiomeric purity (50% ee) but not for the enantiomerically pure compound (99% ee). The release rate of (-)-terpinen-4-ol (99% ee) was shown to be an important factor. For the combination of frontalin and (-)-terpinen-4-ol (50% ee), the attraction seemed strongest when (-)-terpinen-4-ol was released at a higher rate than frontalin. An interesting and novel result was that a repellent compound, a-terpineol, was identified in our studies. Our results from field studies and electroantennography recordings also indicate that (+)-terpinen-4-ol is a repellent for P. poligraphus.


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