Abstract: Experiments were conducted to enhance the virulence of two isolates of entomopathogenic fungi, IRAN-187C of Beauveria bassiana (Balsamo) Vuillemin, and A-396 isolate of Metarhizium anisopliae (Metschnikow) Sorokin, by combination with InsectoSec formulation of diatomaceous earth (DE) against the adults of Callosobruchus maculatus F. under laboratory conditions. The results demonstrated that the combinations between diatomaceous earth and the fungal isolates at lethal and sub-lethal doses achieved high mortality rates in the adult populations; moreover, the treatments improved LT₅₀ values of the fungi. The lowest value of LT₅₀ (122.2 h) was achieved by LC₅₀ (B. bassiana, IRAN-187C) + LC₅₀ (DE) treatment which was on par with that of LC₅₀ (M. anisopliae, A-396) + LC₅₀ (DE) combination (128.2 h) based on their 95% fiducial limit values, resulting in better efficacy of each fungal isolate in combination with diatomaceous earth against C. maculatus adults. Also, effects of the three temperatures (22, 27, and 30℃) and two relative humidity levels (40% and 55%) on the activity of diatomaceous earth when applied against C. maculatus adults showed that the least value of LT₅₀ (110.11 h) was attained in 30℃ and RH of 40%, suggesting high activity of diatomaceous earth in high temperatures and low humidity conditions.

Key words: Callosobruchus maculatus; Beauveria bassiana; Metarhizium anisopliae, diatomaceous earth, virulence, median lethal concentration (LC₅₀ ), median lethal time (LT₅₀), mortality