Terpene detoxification in pine weevils

Many microorganisms are known to engage in symbiotic relationships with insect hosts for which they provide different compounds. Given the diverse metabolic capabilities of symbiotic microorganisms, it has been proposed that in addition to synthesizing and providing a range of nutritional supplements for their hosts, they can be involved in detoxification of noxious chemicals.  This has already been demonstrated for mutualistic yeasts (Shen and Dowd 1991) and filamentous fungi (De Fine Licht et al. 2012), but remains elusive for mutualistic bacteria. Recently, it has been shown experimentally that pesticide-resistant strains of Burkholderia can establish stable symbiotic relationships with broad-headed bugs, and they confer the resistance to their host (Kikuchi et al. 2012). As opposed to most other known insect-bacteria symbioses, however, the bug-Burkholderia symbiosis is characterized by a high degree of flexibility, with environmental acquisition of the symbionts in every host generation. It is so far unknown whether co-evolved symbionts can also provide protection against naturally occurring toxic compounds.

The pine weevil (Hylobius abietis) is a pest for European conifer forests, where they feed on the bark and phloem of pine and spruce. It spends its whole life in close contact to terpenes (the conifer’s main chemical defense). Other insects are known to be highly susceptible to these compounds, which have often been found to act as antifeedants and deterrents and can cause neural damage and disruption of the gut membrane. However, they have little or no negative effect on the pine weevil.

In collaboration with Axel Schmidt and Jonathan Gershenzon (Department of Biochemistry), we are studying how Hylobius abietis copes with terpenes in its diet and whether its gut microbiota is involved in the detoxification of these compounds.  We are using culture-dependent and molecular methods to characterize the microorganisms present in the weevil’s gut, as well as metabolic and genomic analyses to assess their function. This study can shed some light on how insects deal with plant chemical defenses and how symbioses could help insects to colonize new ecological niches.