Improving efficacy of the entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae against Sitophilus zeamais through polyamine application

Post-harvest pests cause large losses worldwide, threatening the global food security due to the reduction of the quality and quantity of grains. Traditional management strategies are based on the use of chemical pesticides and grain protectants, most of which are toxic not only to pest, but also cause damage to the environment and insect resistance. Biological control strategies based on the use of entomopathogenic fungi offer an eco-friendly alternative to agrochemical products. Besides, strategies combining other compounds and organisms to improve the effectiveness of entomopathogenic fungi has been described. Polyamines are essential molecules present in all organisms, in fungi, their physiological functions include regulation of growth, morphogenesis, and stress tolerance. In the present research, the effect of polyamines on germination, viability, and virulence in entomopathogenic fungi to improve the efficiency of controlling insect pests was studied. Conidia of Beauveria bassiana and Metarhizium anisopliae were treated with putrescine, spermidine, and spermine, and a positive effect was observed on spore germination, viability, and an increase was shown in insect mortality in treated spores. Metarhizium anisopliae treated with putrescine and spermidine 0.5 mM, achieved a mortality of 77% and 92%, respectively, compared with 42% of the control. Similarly, B. bassiana treated with spermidine caused a mortality of 65% using 0.1 mM, and 75% with 0.5 mM. Our results suggest that polyamines increased the efficiency of M. anisopliae and B. bassiana conidia against S. zeamais, which might be extrapolated to another pest insect with potential for open-field applications.