FATE AND SURVIVAL OF MICROBIAL PEST-CONTROL AGENTS IN NONTARGET AQUATIC ORGANISMS

A fully enclosed test system was developed both to assess potential ad verse effects of microbial pest control agents on nontarget aquatic in vertebrates and to monitor their fate and survival. Eastern oysters Cr assostrea virginica were exposed to various microbial pest control age nts including the vegetative bacterium Pseudomonas fluorescens, bacter ial spores of Bacillus sphaericus, and fungal spores of Colletotrichum gloeosporioides f. sp. aeschynomene. After an exposure of 3 d for the fungus, 14 d f or the bacterial spores, and 7 d f or the vegetative b acterial cells, half the oysters were placed into a fully enclosed 60 1 aquarium equipped with a recirculating water system which passed wat er through an ultraviolet-irradiation sterilizer at a rate of 11 min-1 . The remaining oysters were placed into wire cages maintained in Sant a Rosa Sound, Pensacola, Florida, USA. Plate counts, performed on homo genized oyster tissues, revealed that all of the microbial pest contro l agents were found in oysters after exposure. Oysters depurated each microorganism at a different rate. None of the agents colonized the oy sters. For all microbes tested, rates of clearance from the oysters in the enclosed UV light depuration system were similar to rates of clea rance from the oysters in Santa Rosa Sound. Histological examination o f oyster tissues detected P fluorescens and B. sphaericus in the gut a nd C. gloeosporioides in the gill. Spore germination was not observed and no apparent signs of infectivity or pathogenicity were detected.