Pseudomonas fluorescens CHA0 and the related strain Pf-5 are well-characterized representatives of rhizosphere bacteria that have the capacity to protect crop plants from fungal root diseases, mainly by releasing a variety of exoproducts that are toxic to plant pathogenic fungi. Here, we report that the two plant-beneficial pseudomonads also exhibit potent insecticidal activity. Anti-insect activity is linked to a novel genomic locus encoding a large protein toxin termed Fit (for P. fluorescensinsecticidal toxin) that is related to the insect toxin Mcf (Makes caterpillars floppy) of the entomopathogen Photorhabdus luminescens, a mutualist of insect-invading nematodes. When injected into the haemocoel, even low doses of P. fluorescens CHA0 or Pf-5 killed larvae of the tobacco hornworm Manduca sexta and the greater wax moth Galleria mellonella. In contrast, mutants of CHA0 or Pf-5 with deletions in the Fit toxin gene were significantly less virulent to the larvae. When expressed from an inducible promoter in a non-toxic Escherichia coli host, the Fit toxin gene was sufficient to render the bacterium toxic to both insect hosts. Our findings establish the Fit gene products of P. fluorescens CHA0 and Pf-5 as potent insect toxins that define previously unappreciated anti-insect properties of these plant-colonizing bacteria.

The European cherry fruit fly, Rhagoletis cerasi (L.) (Diptera: Tephritidae), is a highly destructive pest. The low tolerance for damaged fruit requires preventive insecticide treatments for a marketable crop. The phase-out of old insecticides threatens cherry production throughout the European Union (EU). Consequently, new management techniques and tools are needed. With the increasing number of dwarf tree orchards covered against rain to avoid fruit splitting, crop netting has become a viable, cost-effective method of cherry fruit fly control. Recently, a biocontrol method using the entomopathogenic fungus Beauveria bassiana has been developed for organic agriculture. However, for most situations, there is still a lack of efficient and environmentally sound insecticides to control this pest. This review summarizes the literature from over one hundred years of research on R. cerasi with focus on the biology and history of cherry fruit fly control as well as on antagonists and potential biocontrol organisms. We will present the situation of cherry fruit fly regulation in different European countries, give recommendations for cherry fruit fly control, show gaps in knowledge and identify future research opportunities.

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Cabbage root fly (Delia radicum L.) control represents a major challenge in brassica production, therefore different management strategies for its control were tested in conventionally managed open field cauliflower production. Strategies included treatments with low-risk methods such as nitrogen lime, the insecticide spinosad and the Beauveria bassiana ATCC 74040-based biopesticide Naturalis. Their effects were compared with treatments based on nonformulated fungal species Metarhizium brunneum, B. bassiana, Clonostachys solani, Trichoderma atroviride, T. koningiopsis, and T. gamsii and commercial insecticides λ-cyhalothrin and thiamethoxam. Spinosad and thiamethoxam were pipetted to individual plants before transplanting; λ-cyhalothrin was sprayed after transplanting; nitrogen lime was applied at first hoeing. Nonformulated fungi were delivered onto cauliflower plantlets' roots as a single pretransplantation inoculation. The cabbage root fly population dynamics exhibited a strong spatiotemporal variation. The lowest number of cabbage root fly pupae recovered from cauliflower roots in the field experiments was recorded in plants treated with spinosad (significant reduction), followed by Naturalis and one of the tested M. brunneum strains (nonsignificant reduction). Significantly more pupae were counted in the nitrogen lime treatment. The field experiments showed that a single drench of cauliflower plantlets with spinosad offered consistent and enduring cabbage root fly control. Naturalis and nonformulated fungal isolates did not decrease cabbage root fly pressure significantly, apparently due to lack of statistical power. The implications of the substantial intra-and inter-annual pest pressure variation and the benefits of using single plant treatments are discussed, and recommendations for improvement of rhizosphere-competence utilizing biological control strategies provided.