Entomopathogenic fungi are generally considered to be efficacious only in conditions of high ambient moisture. When Beauveria bassiana and/or diatomaceous were applied to wheat kernels onto which adult female Rhyzopertha dominica were introduced and incubated at 26, 30, 32.5 or 34C, the beetle mortalities were greater among those held at 43% RH than those held at 75% RH. Emergence of adult progeny of the introduced beetles was significantly lower in all treatments and temperatures at 43% RH than at 75% RH. On grain that was treated with both the fungus and the dust, there were 95-97% reductions in progeny vs. controls at 43% RH and 22-91% reductions at 75% RH. On grain that was treated with 200 mg/kg of fungus alone, there were 82-90% reductions in progeny at 43% RH and only 7.5-76% reductions at 75% RH. Reductions in progeny on fungus-treated grain were greatest at 26C. A temperature of 34 had a significant negative impact on Beauveria bassiana efficacy at 75% RH, but not at 43% RH. The emergence of control progeny adults was significantly lower at 43% RH than at 75% RH, suggesting that stress contributes to the greater fungus and DE effects at the lower humidity. Greater loss of B. bassiana conidia viability at 75% RH than at 43% RH also contributed to the surprising humidity effect.
Species 1: Moniliales Moniliaceae Beauveria bassiana
Species 2: Coleoptera Bruchidae Rhyzopertha dominica (lesser grain borer)
Keywords: biological control, entomopathogenic fungi
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