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Aims: Faecal pellets from germ-free locusts were used as culture media to determine the ability of locust gut bacteria to synthesize phenolic components of the locust cohesion pheromone.

Methods and Results: Inoculation of germ-free faecal pellets with Pantoea agglomerans, a species commonly isolated from locusts, resulted in the release of large amounts of guaiacol and small amounts of phenol, both of which are components of the locust cohesion pheromone. Two other locust-derived species, Klebsiella pneumoniae pneumoniae and Enterobacter cloacae, also produced guaiacol from germ-free faecal pellets, but the opportunistic locust pathogen, Serratia marcescens, did not. The most likely precursor for guaiacol is the plant-derived vanillic acid, which is present in large amounts in the faeces of both conventional and germ-free locusts.

Conclusions: These observations are consistent with previous ones, that locust gut bacteria are responsible for the production of components of the locust cohesion pheromone.

Significance and Impact of the Study: These findings illustrate how an insect can adapt to make use of a common bacterial metabolite produced by one or more of its indigenous gut bacterial species. This observation has implications for our appreciation of insect gut microbiota interactions.