Identification of male produced compounds in the bark beetle Polygraphus subopacus and establishment of (Z)-2-(3,3-dimethylcyclohexylidene)-ethanol as an aggregation pheromone component

Abstract

Bark beetles of the genus Polygraphus have recently been involved in large bark beetle outbreaks in central Sweden, together with the European spruce bark beetle Ips typographus. Three species of Polygraphus can be found in this region; Polygraphus poligraphus, Polygraphus punctifrons and Polygraphus subopacus. Efficient pheromone traps would facilitate further investigations of these species and their role in bark beetle outbreaks. Pheromone compounds have previously been identified in P. poligraphus and P. punctifrons, but not in P. subopacus. Thus, we allowed males and females of P. subopacus to bore in the bark of stem sections of Norway spruce (Picea abies) in the laboratory. Volatile organic compounds from boring insects were sampled with SPME and analysed with GC–MS and several male-specific compounds were observed. The male specific compounds were 3-methyl-3-buten-1-ol, 3-methyl-2-buten-1-ol, 3-methyl-2-butenal, grandisol, fragranol, (Z)-2-(3,3-dimethylcyclohexylidene)-ethanol, (E)-2-(3,3-dimethylcyclohexylidene)-ethanol, (Z)-2-(3,3-dimethylcyclohexylidene)-acetaldehyde, (E)-2-(3,3-dimethylcyclohexylidene)-acetaldehyde, geranial and γ-isogeraniol. (Z)-2-(3,3-dimethylcyclohexylidene)-ethanol, [(Z)-DMCHE], was identified from GC–MS analysis to be the major male-specific compound while the (E)-isomer, [(E)-DMCHE], was found as a minor compound. These two compounds gave positive responses in EAG analyses with antennae from males and females of P. subopacus. Thus, (Z)- and (E)-DMCHE were used in a field experiment in central Sweden but only (Z)-DMCHE was found to be attractive to males and females of P. subopacus. Consequently, (Z)-DMCHE was established to be a component of P. subopacus aggregation pheromone.

Identification of sex-specific compounds in the invasive four-eyed fir bark beetle Polygraphus proximus

“…In four other Polygraphus species, male-specific aggregation pheromones have been found. Polygraphus rufipennis has been shown to use 3-methyl-3-buten-1-ol as their aggregation pheromone (Bowers et al 1991), Polygraphus poligraphus use (−)-(R)-terpinen-4-ol (Schurig et al 1985;Rahmani et al 2015), Polygraphus punctifrons use (+)-(1R,2S)-grandisol and (-)-(R)-terpinen-4-ol as the main components of their aggregation pheromone (Rahmani et al 2019) and Polygraphus subopacus use (Z)-2-(3,3-dimethylcyclohexylidene)ethanol as their main aggregation pheromone component (Viklund et al 2021). It has been shown that bark beetles of the same genus often have overlapping pheromone components (Blomquist et al 2010).…”

“…The aim of this work was to identify pheromone components of P. proximus using solid-phase micro extraction together with gas chromatography and mass spectrometry (SPME-GC-MS). These methods have previously been shown to be useful for pheromone identification in Polygraphus bark beetles (Rahmani et al 2015(Rahmani et al , 2019Viklund et al 2021).…”

“…Many of the sex-specific compounds which were identified in P. proximus have previously been tested for activity on P. subopacus antennae (Viklund et al 2021). Three additional compounds, fragranol, geraniol and 1-hexanol were also tested on P. subopacus, using the same methodology as described by Viklund et al (2021).…”

“…Many of the sex-specific compounds which were identified in P. proximus have previously been tested for activity on P. subopacus antennae (Viklund et al 2021). Three additional compounds, fragranol, geraniol and 1-hexanol were also tested on P. subopacus, using the same methodology as described by Viklund et al (2021). Unfortunately, P. proximus was not available for EAG studies as it is a quarantine species in the European Union (De la Peña et al 2020) and could not be brought to Sweden, where the EAG studies were conducted.…”

“…Racemic fragranol and 7-methyl-3-methylene-6-octen-1-ol (γ-isogeraniol) were synthesized at our laboratory. These syntheses have been described previously (Rahmani et al 2019;Viklund et al 2021;Yong et al 2001). Papayanol was synthesized at our laboratory starting from racemic grandisol, according to the method described by Zarbin et al (2010).…”