Influence of Ultraviolet Light Protectants on Persistence of the Entomopathogenic Fungus, Beauveria bassiana

The effect of ultraviolet light (uv) protectants on persistence of conidia of the entomopathogenic fungus Beauveria bassiana was investigated in laboratory and field environments. The survival of conidia applied in water onto glass coverslips or crested wheatgrass (Agropyron cristatum) leaves was reduced by greater than 95% after 15 min exposure to uv-B radiation in a controlled environment. Substitution of oil for water increased the survival of conidia on both substrates. However, conidial survival in oil was more pronounced on glass (74% mortality after 60 min) than on leaves (97% mortality after 60 min). The decreased protection provided by oil on leaves was attributed to spreading and/or absorption of the oil by the leaf tissues. None of 21 potential sunscreen formulations were toxic to nongerminated conidia in vitro. On wheatgrass leaves, 5 of the 12 water-compatible and two of the nine oil compatible formulations enhanced survival of conidia after 3 h exposure to uv-B radiation in a controlled environment. Four water-compatible and three oil-compatible sunscreen adjuvants were subsequently tested in a repeated held experiment. The water-compatible fluorescent brightener, Tinopal LPW (conidial survival slopes of −2.1 and −1.7 in trials one and two, respectively), and a clay emulsion (slopes of −2.5 and −2.0) significantly increased survival of conidia compared to the water control (slopes of −3.3 and −2.7), whereas Congo Red (slopes of −3.1 and −2.8) and the optical brightener, Blankophor BSU (slopes of −4.2 and −3.7), were ineffective. Conidial survival in the field was not enhanced by the three oil-compatible adjuvants tested (oxybenzone, octyl-salicylate, and ethyl-cinnamate). The use of uv-B protectants in formulations can increase conidial survival and may enhance the efficacy of B. bassiana for controlling insect pests in epigeal habitats.