Verbenone—the universal bark beetle repellent? Its origin, effects, and ecological roles

Abstract

Bark beetles (Curculionidae: Scolytinae) spend most of their life in tissues of host plants, with several species representing economically relevant pests. Their behaviour is largely guided by complex olfactory cues. The compound verbenone was discovered early in the history of bark beetle pheromone research and is now sometimes referred to as a ‘universal bark beetle repellent’. However, some studies aiming to protect trees with verbenone have failed. In fact, most research effort has gone into applied studies, leaving many questions regarding the ecological functions of verbenone for various species unanswered. Here, we review and analyse the scientific literature from more than 50 years. Behavioural responses to verbenone are common among pest bark beetles (< 1% of scolytine species studied so far). Indeed, attraction is inhibited in 38 species from 16 genera, while some secondary species are unaffected or even attracted to verbenone. It is not clear whether the beetles can control the biosynthesis of verbenone; its release may not be an active signal by the beetles, but a passive cue resulting from microorganisms during host colonisation. In this context, we advocate to recognise a bark beetle and its microbiome as an entity (‘holobiont’), to better understand temporal release patterns and deduce the specific function of verbenone for a given species. Surprisingly, natural enemies are not commonly attracted by verbenone, but more taxa need to be studied. A better understanding of the ecological functions of verbenone will help to make verbenone-based tools more effective and improve integrated pest management strategies.

Know When You Are Too Many: Density-Dependent Release of Pheromones During Host Colonisation by the European Spruce Bark Beetle, Ips typographus (L.)

“…Together with specific concentrations of ipsenol (Birgersson et al 1984 ; Xie and Lv 2013 ), it inhibits the attraction of aggregation-pheromones (Bakke 1981 ) and these two compounds were thus suggested to regulate intraspecific competition (Vité and Francke 1985 ). Even though verbenone is known since decades, it is still not clear how well its emission is actually related to colonisation densities and whether it is also an actively produced beetle signal or simply a passive cue originating from degraded substrate (Frühbrodt et al 2023 ).…”

Antenna-Biased Odorant Receptor PstrOR17 Mediates Attraction of Phyllotreta striolata to (S)-Cis-Verbenol and (−)-Verbenone

“…Verbenone and verbenol are not only identified as pheromone components of many species of Dendroctonus, Tomicus, Pityogenes, and Ips [41], but also released by various gymnosperm tree species [42,43] and angiosperm species [10,11]. Currently, verbenone and verbenol are recognized as "universal bark beetle repellents" due to their effective repellent properties [12]. In addition to working as beetle repellents, verbenone and verbenol also attract other insects.…”

“…Odorants (−)-verbenone and (S)-cis-verbenol can be found in various common bark beetle host species, as well as in various angiosperm species such as Brassica and Sinapis, which are host plants of P. striolata [10,11]. Behavioral responses to verbenone and verbenol are common among pest bark beetles, and these have shown considerable potential in management [12]. However, the molecular mechanisms underlying the detection of (−)-verbenone and (S)-cis-verbenol remain unclear.…”

Field effects of oxygenated monoterpenes and estragole combined with pheromone on attraction of Ips typographus and its natural enemies

“…In the protection of Norway spruce trees against I. typographus, verbenone, a well-established repellent for bark beetles, was tested with varying success (Jakuš et al, 2003;Frühbrodt et al, 2023). In nature, verbenone signals an old and over-exploited host.…”