Quality of Beauveria bassiana conidia after successive passages through Alphitobius diaperinus (Coleóptera: Tenebrionidae)

The vegetative growth, conidial production, conidial yield on rice, virulence, and heat and UV radiation tolerances of Beauveria bassiana after successive passages through Alphitobius diaperinus were investigated. Three strains of B. bassiana were cultivated in a culture medium, and passed them up to 15 times through the host insect. The conidia of each strain, derived from dead insects, were cultivated in a culture medium. We used conidia corresponding to the first, fifth, tenth, and fifteenth passages in our experiments. Our results showed that successive passages of the fungus through the host insect affected the quality of the conidia; moreover, the effect on conidial quality varied among the strains. For strains Unioeste 4 and Unioeste 40, successive passages through the host insect resulted in reduced vegetative growth and conidial production. In contrast, vegetative growth and conidial production of strain CG 152 were unaffected by successive passages through the host insect. For all 3 strains, successive passages through the host insect resulted in a higher conidial yield on rice and increased virulence, especially after the tenth and fifteenth passages. In addition, an increase in the number of passages through the host insect led to a decrease in the UV radiation tolerance, but an increase in the heat tolerance, especially after the tenth and fifteenth passages. Our results indicate that the conidial yield on rice, virulence, and heat tolerance of B. bassiana are favored by successive passages through A. diaperinus.