Earthworms smell microorganisms in soil
Zirbes, Lara1; Verheggen, François J.1; Mescher, Mark2; Wathelet, Jean-Paul3; Thonart, Philippe4; Haubruge, Eric1
1Gembloux Agro-Bio Tech University of Liege, Department of Functional and Evolutionary Entomology, Gembloux, Belgium
http://www.fsagx.ac.be/zg/; entomologie.gembloux@ulg.ac.be
2Pennsylvania State University, Center for Chemical Ecology, Department of Entomology, Pennsylvania, USA. 3Gembloux Agro-Bio Tech University of Liege, Laboratory of General and Organic Chemistry, Gembloux, Belgium.
4Gembloux Agro-Bio Tech University of Liege, Laboratory of Bioindustries, Gembloux, Belgium. 1. Context
Olfaction is a key sensory modality by which animals, and many other organisms, acquire information about their surrounding world. Earthworms olfaction is still poorly studied whereas chemoreceptors have been identified on earthworms’ prostonium and buccal epithelium, and have been shown to detect sucrose, glucose and quinine. However, previous studies exploring the feeding strategies of various earthworm species suggest that these animals exhibit orientation and movement toward particular food sources. Perception of volatiles emitted by food sources could be at the origin of earthworm preference.
2. Objectives
We explored the hypothesis that earthworms, Eisenia fetida, use volatile chemicals associated with the soil fungus Geotrichum candidum, one of their important food source, during their foraging behaviour.
3. Results
3.1. Food perception
In a four-arm olfactometer we have placed 20 earthworms in the central chamber and exposed them to G. candidum filtrate
e a rt h w o rm s n u m b e r in e a ch a rm o f th e o lf a ct o m e te r a t th e e n d o f th e e xp e ri m e n t 3.2. Volatile analyses
Eight volatile compounds emitted by G.
candidum filtrate were sampled with SPME,
analysed and identified by GC-MC.
3.3. Volatile perception
Authentic standards of eight molecules were tested separately in the four-arm olfactometer. Two esters exhibited significant attraction to E. fetida: ethyl pentanoate (χ²3= 0.3105, p < 0.001) and ethyl hexanoate (χ²3= 0.2173, p < 0.001)
4. Conclusion
Our results clearly demonstrate that E. fetida are attracted by olfactory cues associated with G. candidum, and thus complement previous reports that earthworms are able to actively search for food sources. To the best of our knowledge, no previous studies have identified specific olfactory cues used by earthworms.
exposed them to G. candidum filtrate (three remaining arms were controls). G.
candidum filtrate strongly attracted earthworms (χ²3= 34.44, p < 0.001)
International Society of Chemical Ecology - 27th Annual Meeting - 24-28 July 2011
G. candidum Control 1 Control 2 Control 3
T o ta l e a rt h w o rm s o f th e o lf a ct o m e te r e xp e ri m e n t Ethyl acetate 2-methylpropan-1-ol Ethyl propionate 3-methylbutan-1-ol 2-methylbutan-1-ol Ethyl pentanoate 3-octanone Ethyl hexanoate G. candidum filtrate GC/MS SPME fiber No attraction A tt ra ct io n
Control 1 Control 2 Control 3
EP T o ta l e a rt h w o rm s n u m b e r in e a ch a rm o f th e o lf a ct o m e te r a t th e e n d o f th e e xp e ri m e n t
