Action of Beauveria caledonica against the banana weevil and the fungi that cause fusariosis extends its potential in biological control The Beauveria caledonica fungus not only works against banana fusariosis (Panama disease) but its strains also have potential for the management of the 'banana weevil' or 'banana root borer' (Cosmopolites sordidus), two of the main phytosanitary problems of the crop. Still little studied in Brazil and in the world, the species was recently isolated by scientists from Embrapa, University of Campinas (Unicamp), Brazil, and from Bioversity International, Colombia, for pest control, especially beetles. Embrapa Environment's analyst Gabriel Mascarin highlights the dual aptitude of the fungus that was found in the commercial banana production region of Registro, São Paulo, Brazil. 'In our research, we isolated adult banana weevils collected in the field and then we made an emulsifiable oil formulation to increase effectiveness and accelerate the process of infection and pest control', Mascarin explains. 'Besides, comparatively, B. caledonica isolates were shown to be more efficient in controlling adult weevils, which emphasizes their potential for the biocontrol of this insect. We also discovered that this fungus produces a secondary compound called oosporein, which had antagonistic action on Fusarium. This effect is unprecedented', explains Mascarin. Oosporein was detected and quantified by the team led by professor Ljubica Tasic from the Institute of Chemistry at Unicamp. 'In an in vitro test against Fusarium, we found that the filtrates that were extracted from the fermented broth of B. caledonica and that had oosporein showed antifungal activity, which resulted in strong inhibition of phytopathogen germination', Mascarin adds. 'This result expands our knowledge on the spectrum of B. caledonica's activity, which is very important for science, considering its antifungal role against this pathogen that is destructive to banana trees', the analyst says. Main banana diseases Weevil and fusariosis are among the main pests and diseases of banana trees, respectively. The insect causes a direct effect on the rhizome, which weakens the plant's root system, reduces nutrient absorption and causes significant losses in productivity. Adult beetles also contribute to the spread and exacerbation of infections by soil plant pathogens. Banana fusariosis spreads rapidly through various means, and causes severe yield losses in banana. A combination of management practices in commercial plantations is necessary to mitigate increases of weevil populations and the incidence of the fungi. However, controlling these organisms is still a major challenge for farmers, and it is very important to search for biological control alternatives to complement field management. The soil is an important reservoir of entomopathogenic fungi (specific against insects) because it is a place where insect pathogens can infect their hosts and then multiply, persist, and grow. So understanding the interaction between C. sordidus – causal agent of fusariosis – and entomopathogenic fungi, as well as understanding how both can relate to other microorganisms in the soil, is crucial for the development of fungal biopesticides. It has been proved that certain commercial banana plantations, infested by the banana weevil, can harbor a very specialized community of entomopathogenic fungal species. It is interesting to note that all three strains of B. caledonica that were naturally isolated from C. sordidus were able to produce and secrete the red pigment known as oosporein in both agar-based and liquid media, although no sign of this pigment was observed for the other strains of Beauvaria bassiana – a fungal species with a broad spectrum of action on pest insects, including several species of agricultural importance. This secondary metabolite may be related to the fungi's greater virulence towards the banana weevil, although this should be further investigated. 'To accelerate the rate and increase the weevil's mortality rate through our best B. caledonica isolate, we made a formulation of the fungi's conidia and an emulsifiable plant oil that is fully biodegradable, which shows that the oil probably plays an important role in the adhesion of the fungi to the insect's body and facilitates its infection', Embrapa Environment's researcher Jeanne Prado explains. According to Embrapa Genetic Resources and Biotechnology's researcher Rogerio Biaggioni Lopes, the development of biopesticides with strains that are more virulent towards the target insect, whether through laboratory selection, formulation, new application strategies or genetic manipulation, can make this microorganism more competitive for use in banana weevil management programs, which contributes to more balanced cultivation systems. 'As far as we know, there are no commercial products made from this microorganism. Brasil has come out ahead, but we have a long way to go in search of an effective biological product in the simultaneous control of this pest and this disease in bananas', Mascarin says. The study by Gabriel Mascarin, Jeanne Prado and Márcia Assalin, from Embrapa Environment; Lucas Gelin Martins, Erik Sobrinho Braga and Ljubica Tasic, from Unicamp; Miguel Dita, from Bioversity International, Cali, Colombia; and Rogerio Lopes, from Embrapa Genetic Resources and Biotechnology, was published in the journal Pest Management Science and can be visited here. The research was funded by the São Paulo Research Foundation (Fapesp).