Comparative genomics of a bacterium associated to Ips typographus: implications for pest insect ecology

The European Norway spruce bark beetle Ips typographus (Coleoptera:Curculionidae: Scolytinae) is a major forest pest, inflicting substantial economic and ecological damage in Europe and beyond. This beetle harbors a complex microbiota and Erwinia typographi is its most abundant bacterial associate. This bacterium showcases characteristics that could potentially benefit its insect host by providing resistance to plant toxins, antifungal activity, and plant polysaccharide degradation. The putative symbiont is vertically transmitted and can be found in all life stages of its host. Notably, other Erwinia spp. associated with a range of Scolytinae beetles form an isolated cluster within the Erwiniaceae family that share similar functions. However, the nature of the interaction between these bacteria and their hosts remains unclear. This study hypothesizes that E. typographi serves as a facultative symbiont of I. typographus, offering benefits for the survival and performance of the pest insect. This hypothesis was tested with a comparative analysis of the genomes of E.typographi and its close relatives from other Scolytinae beetles to reference genomes in the genus Erwinia including bacteria acting as insect symbionts, plant pathogens, and non-pathogenic endophytes. The study followed a quantitative and qualitative approach focused on identifying genes linked to functions that could contribute to a facultative symbiosis with I. typographus and its interactions with the host plant. This approach helped to understand the association between E.typographi and its relatives with Scolytinae beetles, providing important insights into the ecology and management strategies of forest pest insects.