Safety of microorganisms intended for pest and plant disease control: a framework for scientific evaluation

Microorganisms are enormous but largely untapped natural resources for biological control of pests and diseases. There are two primary reasons for their underployment for pest or disease control: (1) the technical difficulties of using microorganisms for biological control, owing to a lack of fundamental information on them and their ecology, and (2) the costs of product development and regulatory approvals required for each strain, formulation, and use. Agriculture and forestry benefit greatly from the resident communities of microorganisms responsible for naturally occurring biological control of pest species, but additional benefits are achieved by introducing/applying them when or where needed. This can be done as (1) an inoculative release, (2) an augmentative application, or (3) an inundative application. Because of their specificity, different microbial biocontrol agents typically are needed to control different pests or the same pest in different environments. Four potential adverse effects are identified as safety issues (hazards) associated with the use of microorganisms for the biological control of plant pests and diseases. These are: (1) displacement of nontarget microorganisms, (2) allergenicity to humans and other animals, (3) toxigenicity to nontarget organisms, and (4) pathogenicity to nontarget organisms. Except for allergenicity, these are the same attributes that contribute to the efficacy of microbial biocontrol agents toward the target pest species. The probability of occurrence of a particular adverse nontarget effect of a microbial biocontrol agent may be a function of geographic origin or a specific trait genetically added or modified, but the safety issues are the still the same, including whether the microorganism intended for pest or disease control is indigenous, nonindigenous (imported and released), or genetically modified by traditional or recombinant DNA (rDNA) technology. Likewise, the probability of occurrence of a particular adverse nontarget effect may vary with method of application, e.g., whether as an aerosol, soil treatment, baits, or seed treatment, and may increase with increased scale of use, but the safety issues are still the same, including whether the microorganism is used for an inoculative release or augmentative or inundative application. Existing practices for managing microorganisms in the environment (e.g., plant pathogens, Rhizobium, plant inoculants) provide experience and options for managing the risks of microorganisms applied for pest and disease control. Moreover, experience to date indicates that any adverse nontarget effects, should they occur, are likely to be short-term or transitory effects that can, if significant, be eliminated by terminating use of the microbial biocontrol agent. In contrast, production agriculture as currently practiced, such as the use of tillage and crop rotations, has significant and long-term effects on nontarget organisms, including the intentional and unintentional displacement of microorganisms. Even the decision to leave plant pests and diseases unmanaged could have significant long-term environmental effects on nontarget organisms. Potential safety issues associated with the use of microbial biocontrol must therefore be properly identified and compared with the impact of other options for managing the pest or leaving the pest unmanaged. This paper provides a scientific framework for this process.