Volatile organic compounds influence the interaction of the Eurasian spruce bark beetle (Ips typographus) with its fungal symbionts

Martin N. Andersson,Almuth Hammerbacher,Dineshkumar Kandasamy,Jonathan Gershenzon

doi:10.1038/s41396-019-0390-3

Martin N. Andersson, Almuth Hammerbacher + Show 2 more

Open Access

https://doi.org/10.1038/s41396-019-0390-3

Copy DOI

Abstract

Insects have mutualistic symbioses with a variety of microorganisms. However, the chemical signals that maintain these insect−microbe relationships are poorly known compared to those from insect−plant symbioses. The spruce bark beetle, Ips typographus, the most destructive forest pest in Europe, has a symbiotic relationship with several fungi that are believed to contribute to its successful invasion of Norway spruce. Here we tested the hypothesis that volatile organic compounds (VOCs) emitted from fungal symbionts could be cues for bark beetles to recognize and distinguish among members of its microbial community. Behavioral experiments with fungi showed that immature adults of I. typographus are attracted to food sources colonized by their fungal symbionts but not to saprophytic fungi and that this attraction is mediated by volatile cues. GC-MS measurements revealed that the symbionts emitted VOCs. Testing the activity of these compounds on beetle antennae using single sensillum recordings showed that beetles detect many fungal volatiles and possess olfactory sensory neurons specialized for these compounds. Finally, synthetic blends of fungal volatiles attracted beetles in olfactometer experiments. These findings indicate that volatile compounds produced by fungi may act as recognition signals for bark beetles to maintain specific microbial communities that might have impact on their fitness.

Highlights

Wood-boring insects, like many other organisms, often engage in associations with symbiotic microorganisms to fulfill a range of physiological and ecological functions [1, 2]
To determine if the spruce bark beetle, I. typographus, can recognize individual fungi frequently associated with beetle galleries and distinguish among them, we developed a behavioral assay in a Petri dish arena where callow
Using 4-day-old cultures, we found that callow adult beetles were attracted to volatiles originating from three species of fungi: E. polonica, G. penicillata, and G. europhioides, with stronger a b c

Summary

Introduction

Wood-boring insects, like many other organisms, often engage in associations with symbiotic microorganisms to fulfill a range of physiological and ecological functions [1, 2]. The need of wood-boring insects for symbionts may be ascribed to the nature of their substrate, which is generally low in nutrients and high in toxic defense chemicals.

Methods

Results

Conclusion