Pine monoterpenes and pine bark beetles: a marriage of convenience for defense and chemical communication

Abstract

Pine-feeding bark beetles (Coleoptera: Scolytidae) interact chemically with their host pines (Coniferales: Pinaceae) via the behavioral, physiological, and biochemical effects of one class of isoprenoids, the monoterpenes and their derivatives. Pine monoterpenes occur in the oleoresin and function as behaviorally active kairomones for pine bark beetles and their predators, presenting a classic example of tritrophic chemical communication. The monoterpenes are also essential co-attractants for pine bark beetle aggregation pheromones. Ironically, pine monoterpenes are also toxic physiologically to bark beetles at high vapor concentrations and are considered an important component of the defense of pines. Research over the last 30 years has demonstrated that some bark beetle aggregation pheromones arise through oxygenation of monoterpenes, linking pheromone biosynthesis to the host pines. Over the last 10 years, however, several frequently occurring oxygenated monoterpene pheromone components (e.g., ipsenol, ipsdienol and frontalin) have also been shown to arise through highly regulated de novo pathways in the beetles (reviewed in Seybold and Tittiger, 2003). The most interesting nexus between these insects and their plant hosts involves the latestage reactions in the monoterpenoid biosynthetic pathway, during which isomeric dimethylallyl diphosphate and isopentenyl diphosphate are ultimately elaborated to stereospecific monoterpenes in the trees and to hydroxylated monoterpenes or bicyclic acetals in the insects. There is signal stereospecificity in both production of and response to the monoterpenoid aggregation pheromones of bark beetles and in response to the monoterpenes of the pines. In the California fivespined ips, Ips paraconfusus, we Dedicated to Professor David L. Wood on the occasion of his 75th birthdayÓ Springer Science+Business Media B.V. 2006have discovered a number of cytochome P450 genes that have expression patterns indicating that they may be involved in detoxifying monoterpene secondary metabolites and/or biosynthesizing pheromone components. Both processes result in the production of oxygenated monoterpenes, likely with varying degrees of stereospecificity. A behavioral analysis of the stereospecific response of I. paraconfusus to its pheromone is providing new insights into the development of an efficacious bait for the detection of this polyphagous insect in areas outside the western United States. In contrast, a Eurasian species that has arrived in California, the Mediterranean pine engraver, Orthotomicus (Ips) erosus, utilizes both a monoterpenoid (ipsdienol) and a hemiterpenoid (2-methyl-3-buten-2-ol) in its pheromone blend. The stereospecificity of the response of O. erosus to the monoterpenoid appears to be the key factor to the improved potency of the attractant bait for this invasive species.

Erwinia typographi sp. nov., isolated from bark beetle (Ips typographus) gut

“…Phytophagous insects, such as bark beetles, feed on conifers, which produce large amounts of terpenes. Terpenes are known to be defensive compounds and many of them are toxic to both herbivorous insects and micro-organisms (Phillips & Croteau, 1999;Keeling & Bohlmann, 2006;Seybold et al, 2006;Gershenzon & Dudareva, 2007;Zhao et al, 2010). Monoterpene myrcene (7-methyl-3-methylene-1.6-octadiene, C 10 H 16 ) is one of the defensive compounds produced by conifers.…”

Pheromone-based Mating and Aggregation in the Sorghum Chafer, Pachnoda interrupta

“…3). In other insects, increased attraction has been observed to combinations of pheromones with volatiles from hosts used for feeding (Klein et al 1981, Seybold et al 2006, oviposition (Dickens et al 1993), or both (Bartelt et al 1985), and shifts in sex ratio of attracted conspecifics when unmated females are combined with food volatiles have been observed in P. japonica (Klein et al 1981) and the diamondback moth, Plutella xylostella (L.) (Reddy and Guerrero 2000). Access to food could also increase pheromone emission by females (McNeil and Delisle 1989), and aggregations might be influenced by pheromone release rate as well as the presence of host volatiles.…”

“…Although individual females only contained an estimated 0.2 ng of PAA, during the mating season, P. interrupta form aggregations with thousands of adults and the effective emission of PAA from one of these aggregations may be quite high. High release rates of semiochemicals have been shown to be necessary for attraction in the Coleoptera, e.g., to pheromone components in Ips typographus (L.) (Schlyter et al 1987) or to host attractant monoterpenes in many other bark beetles (reviewed in Seybold et al 2006). Furthermore, the involvement of additional components in the pheromone communication system of P. interrupta cannot be ruled out, and the inclusion of such compounds might enhance the specificity of the signal, and lower the threshold for response (Linn et al 1986).…”

Volatile terpenoids: multiple functions, biosynthesis, modulation and manipulation by genetic engineering

“…(Krasnyanski et al 1999;Aharoni et al 2005). It has been demonstrated that upon herbivore attack, plants emit a blend of volatiles, which is composed of more than 200 compounds that are directly responsible for deterring, intoxicating or repelling herbivorous insects (Seybold et al 2006). Alternatively, they can attract the parasitoids and natural predators of offending herbivores, resulting in securing the plant from damage (Mercke et al 2004;Degen et al 2004;Dudareva et al 2013).…”