Effectiveness of Metarhizium anisopliae (Metschinkoff) Sorokin applied alone or in combination with diatomaceous earth against Tribolium confusum Du Val larvae: Influence of temperature, relative humidity and type of commodity

Laboratory experiments were carried out in order to assess the insecticidal effect of Metarhizium anisopliae (Metschinkoff) Sorokin (Deuteromycotina: Hyphomycetes) formulations against larvae of Tribolium confusum Du Val (Coleoptera: Tenebrionidae) on flour and wheat. M. anisopliae was applied at three dose rates, of 8×106, 8×108 and 8×1010 conidia/kg to either wheat or flour, respectively. Also the wheat/flour was treated with the diatomaceous earth (DE) formulation SilicoSec (Biofa, Germany), at two dose rates, 0.2 and 0.5 g/kg of wheat or flour either alone or in combination with M. anisopliae with each fungal rate. Mortality of T. confusum larvae was assessed 7 days after exposure to the treated substrate. The bioassays were conducted at three temperatures, 20, 25 and 30 °C, and two relative humidity (r.h.) levels, 55% and 75%. Larval mortality was notably varied among treatments, as well among temperature and humidity levels. For both fungus and DE, the increase of temperature increased their effectiveness. On the other hand, the increase of r.h. significantly reduced larval mortality for both M. anisopliae and SilicoSec. Both substances, either alone or in combination, were more effective on wheat than on flour. Also, the addition of 0.5 g of SilicoSec in the fungal preparation, especially at the highest dose rate, increased larval mortality, in comparison with the fungus alone or in combination with 0.2 g of SilicoSec. The results of the present work suggest that, under certain circumstances, the effectiveness of M. anisopliae against T. confusum larvae can be benefitted by the presence of DE.