Factors in the Success and Failure of Microbial Controlagents for Soil Dwelling Pests

The soil, being rich in microbes, should be an ideal environment in which to practise microbial control of insect pests, but relatively few organisms have been developed into successful microbial control agents for soil pests. Difficulty arises in implementation of microbial control, as the soil is a highly complex, competitive environment where survival of applied microbes is by no means assured. In addition, soil dwelling pests appear to show a high level of resistance to broad spectrum pathogens and microbial toxins. However, some significant successes have been achieved with bacteria, fungi and nematodes for control of a range of soil inhabiting pest species. The successful microbial controls are based on highly specific microbial/insect interactions where co-evolved pathogens can overcome the host's defences. These agents also have the ability to persist in the soil, either through the inherent stability of the organism or from recycling through the host population. While strain selection for high levels of pathogenicity and environmental competence is the essential first step in microbial control of soil dwelling pests, it must be followed by development of efficient production systems and quality control measures to ensure application of standardised, high quality products. Success in microbial control of soil dwelling pests depends on an appropriate combination of these factors, with failure likely to occur if any one of these essential components is overlooked.