Insecticidal effect of Beauveria bassiana (Balsamo) Vuillemin (Ascomycota: Hypocreaes) in combination with three diatomaceous earth formulations against Sitophilus granarius (L.) (Coleoptera: Curculionidae)

The insecticidal effect of the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin (Ascomycota: Hypocreaes) in combination with three diatomaceous earth (DE) formulations against adults of the granary weevil, Sitophilus granarius (L.) (Coleoptera: Curculionidae) was tested in the laboratory. The three DEs were Insecto™, SilicoSec^® and PyriSec^®. The fungus was applied at 400 ppm alone, or in combination with 200 ppm of each of the three DEs. Mortality was measured after 7 d of exposure. Bioassays were conducted at three temperatures 20, 25 and 30 °C and two relative humidities (rh) 55% and 75%. On wheat treated with B. bassiana alone, mortality was higher at 55% than at 75% rh. Also, the fungus alone was less effective at 20 °C than at the other two temperatures tested, but mortality did not exceed 52% for any of the conditions tested. Similar mortality levels were also noted on wheat treated with each of the three DEs alone. The simultaneous presence of B. bassiana and DE increased weevil mortality. In this combination, mortality was higher at high temperatures and low rh, and this effect was similar for all DEs tested. Progeny production on wheat treated with B. bassiana was higher that the respective progeny counts in the DE-treated wheat. The results indicate that a combination of B. bassiana and DEs is effective against S. granarius, under a broad range of temperature and rh levels in stored wheat.