Soil treatments with Metarhizium brunneum EAMa 01/58-Su strain conducted in both Northern and Southern Spain reduced the olive fly (Bactrocera oleae) population density emerging from the soil during spring up to 70% in treated plots compared with controls. A model to determine the influence of rainfall on the conidial wash into different soil types was developed, with most of the conidia retained at the first 5 cm, regardless of soil type, with relative percentages of conidia recovered ranging between 56 and 95%. Furthermore, the possible effect of UV-B exposure time on the pathogenicity of this strain against B. oleae adults coming from surviving preimaginals and carrying conidia from the soil at adult emergence was also evaluated. The UV-B irradiance has no significant effect on M. brunneum EAMa 01/58-Su pathogenicity with B. oleae adult mortalities of 93, 90, 79, and 77% after 0, 2, 4, and 6 of UV-B irradiance exposure, respectively. In a next step for the use of these M. brunneum EAMa 01/58-Sun soil treatments within a B. oleae IPM strategy, its possible effect of on the B. oleae cosmopolitan parasitoid Psyttalia concolor, its compatibility with the herbicide oxyfluorfen 24% commonly used in olive orchards and the possible presence of the fungus in the olive oil resulting from olives previously placed in contact with the fungus were investigated. Only the highest conidial concentration (1 × 10⁸ conidia ml⁻) caused significant P. concolor adult mortality (22%) with enduing mycosis in 13% of the cadavers. There were no fungal propagules in olive oil samples resulting from olives previously contaminated by EAMa 01/58-Su conidia. Finally, the strain was demonstrated to be compatible with herbicide since the soil application of the fungus reduced the B. oleae population density up to 50% even when it was mixed with the herbicide in the same tank. The fungal inoculum reached basal levels 4 months after treatments (1.6 × 10³ conidia g soil⁻¹). These results reveal both the efficacy and environmental and food safety of this B. oleae control method, protecting olive groves and improving olive oil quality without negative effects on the natural enemy P. concolor.

One of the main negative effects of climate change on biological pest control is alteration of relationships between insect pests and their natural enemies (both entomophagous and entomopathogenic). Indeed, environmental conditions can have multiple effects on pest control success when using entomopathogenic fungi (EPF), where conidial depletion, inactivation, and loss in virulence and infectivity can all occur. Appropriate mass production and formulation strategies for EPF can partially solve these problems. However, the only strategy to guarantee high virulence and infectivity is selection of environmentally competent fungal strains that are able to persist in the host environment for the required infection period. This review examines the criteria for selection of environmentally competent EPF. While UV radiation, followed by humidity and temperature, is probably the most important propagule depletion and inactivation factors in epigeal habitats, temperature is most critical for reducing the infectivity and virulence of EPF in epigeal and hypogeal habitats. In addition, geographical origin and other biotic and abiotic factors have an important impact which may guarantee the environmental competence of selected entomopathogenic fungal strains and, therefore, farmer willingness to replace chemicals with mycoinsecticides. To achieve this, it is urgent to promote the development of microbial control solutions adapted to relatively uniform climatic zones through more simplified, targeted, and less costly EPF approval and authorization.

Biocontrol with hypocrealean entomopathogenic fungi (EF) is a key tool to develop Integrated Pest Management (IPM) programs for the progressive replacement of synthetic chemical insecticides with more environmentally friendly pest control measures. These fungi stand out among entomopathogens not only for their contact mechanism of infection through the arthropod integument, but also for developing close associations with plants including the endophytic lifestyle and rhizosphere competence that can enable them to make broader contributions to IPM and crop production. Anyhow, the interaction of EF with the plants incorporates multitrophic complexity at different levels including insect pests, plants, and their natural enemies. The aim of the present review was to gather and summarize all available data on multitrophic interactions of EF. These fungi can influence both the chemical ecology of host-plant selection by insect pests and the host or prey selection by parasitoid or predators, respectively. Moreover, EF treatments are compatible with natural enemies in terms of safety and effectiveness, which could allow biocontrol strategies for their synergistic application in IPM programs. A comprehensive understanding of the impact of these multitrophic interactions in longer term, farm-level real-life biocontrol implementation studies will provide new opportunities in plant protection and production.

The susceptibility of preimaginal and adult olive fruit fly, Bactrocera oleae (Gmelin) (Diptera: Tephritidae), to a strain of the mitosporic ascomyce

Entomopathogenic fungi are multipurpose microorganisms with direct and indirect effects on insect pests. Also, EPF provide multiple benefits to plants by solubilizing minerals and facilitating nutrient acquisition.