The bacterial community of the European spruce bark beetle in space and time

Abstract

The European spruce bark beetle Ips typographus (L.) is a pest causing severe damage to Norway spruce-dominated forests in Europe. Microorganisms play an essential role in the species life history, including nutrition, fitness as well as in overcoming host defenses. Here, we performed high-throughput 16S rRNA metabarcoding of I. typographus across different populations in Europe. We investigated four postglacial refugial areas in Europe and focused specifically on a current bark beetle hot spot in the Dolomites where we compared populations with different epidemiological phases (outbreaking vs. non-outbreaking) and across different seasons (pre-overwintering vs. overwintering). Our results show that the bacterial community structure varied among populations from the refugial areas and geographic regions within the Dolomites. We found a significant difference in the bacterial community between pre-overwintering and overwintering individuals, highlighting a potential role of the microbiome in I. typographus overwintering but we did not find differences between epidemic and endemic populations. The genera Erwinia and Pseudoxanthomonas - previously reported for their role in nutrition and protection from conifer defense compounds - were present in every individual across all populations, suggesting that these taxa form the bacterial core community of I. typographus. Furthermore, several additional bacterial taxa occurred in all populations, but with variable frequencies within and between individuals. This study highlights a complex interaction of various bacterial taxa across different regions and ecological phases of I. typographus populations and provides new insights into the role of microorganisms in the biology of this important pest species.

The Eurasian spruce bark beetle Ips typographus shapes the microbial communities of its offspring and the gallery environment

“…; Figure 2A) and fungi (W. bisporus, O. ramenticola, K. molischiana, and C. amylophila; Figure 2B) throughout their development. These taxa have previously been reported in I. typographus at different life stages (Chakraborty et al, 2023;Veselská et al, 2023), across geographic locations (Chakraborty et al, 2023;Moussa et al, 2023) and seasons (Moussa et al, 2023;Veselská et al, 2023), and regardless of whether the beetle populations were experiencing an endemic or an epidemic phase (Moussa et al, 2023). The consistency of these associations throughout time and space indicates the existence of a common core community in the I. typographus gut (Risely, 2020).…”

“…Although spruce bark beetle-fungi-spruce interactions have been intensively researched, the roles of other microorganisms in the invasive success of I. typographus remain poorly understood. Recent efforts to characterize the bacteria and fungi associated with this insect have increased our knowledge of the taxonomical composition of the fungal and bacterial communities (Fang et al, 2020;Chakraborty et al, 2023;Moussa et al, 2023;Veselská et al, 2023). However, the transmission mode of the microbiota has not been elucidated, as there is a lack of behavioral studies and quantitative data on the microbial loads present throughout the beetle's life cycle.…”

Life-stage and geographic location determine the microbial assemblage in Eurasian spruce bark beetle, Ips typographus L. (Coleoptera: Curculionidae)

“…Alternatively, D. ponderosae was reported to uphold relatively stable gut microbial communities resistant to perturbation (Adams et al, 2013). There are other independent observations with beetles or weevils supporting variable or stable microbial associations across wide geographic locations, making it difficult to generalize (Berasategui et al, 2016;Hernández-García et al, 2018;Moussa et al, 2023). Nevertheless, such variations in symbiont selection and maintenance throughout the life cycle among closely related bark beetles are fascinating in an ecological context and enhance our interest in bark beetles as holobionts.…”

“…Notably, phloem consumption also differs between different life stages of beetles, and the nutritional quality of the host tissues varies after initial colonization, which could also influence microbial community structure. Moreover, different geographic locations can influence the bark beetle-microbial interactions due to the difference in host tree holobiont and environment (Adams et al, 2010;Liu et al, 2019;Moussa et al, 2023). We hypothesize that drivers such as bark beetle life stage and geo-location concurrently influence the ESBB microbial associations, and life stage, which undergoes metamorphosis, have a more predominant role.…”

“…The bacterial and fungal communities associated with the ESBB gut were recently identified using a metagenomic approach, and their potential role in bark beetle adaptation was predicted (Chakraborty et al, 2020a,b). Despite all those efforts, our current knowledge about the geographic location (including microhabitat, i.e., plant holobiont) and life stage influence on ESBB microbial assemblage is still limited and are yet to be conducted on broader geographic conditions (Moussa et al, 2023;Veselská et al, 2023).…”