Shelf-life study of oil-based formulations of Beauveria bassiana enriched with osmoprotectants: effect on conidia germination and efficacy on Diatraea saccharalis

ABSTRACT

Entomopathogenic fungi are important biological control agents of insect pests; however, storage stability is one of the main challenges for their commercialisation. In this study, osmoprotective substances were added to formulation prototypes of a native Beauveria bassiana isolate as a strategy to prolong the efficacy during storage. A three-month accelerated thermo-stability study was conducted as selection criteria. In vitro efficacy (corrected mortality) tests were considered in addition to the microbiological response variables commonly reported in the literature (germination and active ingredient concentration – plate count of colony-forming units). The results allowed to select trehalose as the best osmoprotective substance. This prototype had a lethal concentration (LC₅₀) on Diatraea saccharalis (Lepidoptera: Crambidae) larvae of 2.8×10⁵ conidia mL⁻¹, and its efficacy remained higher than 90% when stored at 6°C and 18°C. Mathematical models were constructed according to efficacy data, the shelf-life of the selected prototype was 36.6 months when stored at 6 ± 2°C, 26.0 months at 18°C, and 5.3 months at 28°C. The obtained results emphasise the importance of shelf-life evaluation based on efficacy data of biological activity in addition to microbiological variables that may not be directly related to efficacy. The current study conclusively demonstrates a relationship between temperature and shelf-life.

KEYWORDS:

• Bioproducts
• fungi
• biocontrol
• pests
• biopesticide
• production

Acknowledgments

The authors would like to thank the ‘Sistema General de Regalías Departamento de Nariño – Colombia’ for financing the project 881-2015 and the Colombian corporation for agricultural research (Agrosavia) for providing material and human resources. Likewise, Sergio Ramírez and Stella Rincón for their willingness to collaborate in all activities proposed.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Authors contribution statement

L.G-R., G.Q-C., and D.F.C-R participated at conceptualisation, performed research, analyzed data, designed, and wrote the paper. C.E. and J.G-V. contributed to conceptualisation, performed research, analyzed data, and wrote the paper. M.G-A. contributed with funding acquisition, conceptualisation, and supervision of the paper.

Additional information

Funding

This work was supported by Corporación Colombiana de Investigación Agropecuaria, AGROSAVIA [grant number 1864]; Sistema General de Regalías de Colombia [grant number 881-2015].