Abstract: The use of Integrated Pest Management (IPM) and of alternative approaches or techniques, such as alternatives to chemical pesticides, are promoted by Directive 2009/128/EC. Alternatives include biological control agents (BCAs). Commercial BCAs are available for the control of Botrytis bunch rot (BBR) on grapevines, caused by Botrytis cinerea, but their use is still limited. One likely reason is their inconsistent efficacy under field conditions, which may be related to several factors, including the environmental conditions affecting both BCA fitness and B. cinerea development. The colonization rate and the efficacy of a specific BCA, as well as B. cinerea growth and infection, are all influenced by weather conditions, such as temperature and moisture. To achieve an effective integration of BCAs in a disease management program is then relevant to know: i) the life cycle of both, the pathogen and the BCA; ii) the mode of action of the BCA against the target pathogen; and iii) how the two are influenced by the environmental conditions. The concept of “environmental niches” is proposed in this work to understand how the environmental conditions influence the BCA – pathogen interaction. Environmental niches are defined as the environmental conditions necessary for the presence of a species and the maintenance of its population. In this work, this concept was used to study the temperature and humidity conditions under which two BCA-based products prevail over B. cinerea, and to define the extent of environmental niche sharing between each BCA and the target pathogen.