CHEMICAL BARRIERS TO GUT INFECTION IN THE DESERT LOCUST - IN-VIVO PRODUCTION OF ANTIMICROBIAL PHENOLS ASSOCIATED WITH THE BACTERIUM PANTOEAAGGLOMERANS

Antifungal phenols, absent from fecal pellets of germ-free desert locu sts, Schistocerca gregaria, were found in the fecal pellets of locusts which had been monoassociated with Pantoea agglomerans. In addition, gut fluid from monoassociated insects was inhibitory to germination of conidia of Metarhizium anisopliae, whereas gut fluid from germ-free l ocusts was not. It is concluded that P. agglomerans probably produced the phenols. The presence in fecal pellets from monoassociated insects of only one of the three phenols identified from conventional insects and the occurrence of another fungitoxic: phenol suggest that in conv entional insects a number of bacteria including P. agglomerans coopera te in the production of the phenols. The antifungal phenols are also s electively bacteriocidal and it is suggested that the toxins may have a wide role in host defense against pathogenic microorganisms and a si gnificant impact on the composition of the gut flora. (C) 1995 Academi c Press, Inc.