INFLUENCE OF ULTRAVIOLET-LIGHT PROTECTANTS ON PERSISTENCE OF THE ENTOMOPATHOGENIC FUNGUS, BEAUVERIA-BASSIANA

The effect of ultraviolet light (uv) protectants on persistence of con idia of the entomopathogenic fungus Beauveria bassiana was investigate d in laboratory and field environments. The survival of conidia applie d in water onto glass coverslips or crested wheatgrass (Agropyron cris tatum) leaves was reduced by greater than 95% after 15 min exposure to uv-B radiation in a controlled environment. Substitution of oil for w ater increased the survival of conidia on both substrates. However, co nidial survival in oil was more pronounced on glass (74% mortality aft er 60 min) than on leaves (97% mortality after 60 min). The decreased protection provided by oil on leaves was attributed to spreading and/o r absorption of the oil by the leaf tissues. None of 21 potential suns creen formulations were toxic to nongerminated conidia in vitro. On wh eatgrass leaves, 5 of the 12 water-compatible and two of the nine oil compatible formulations enhanced survival of conidia after 3 h exposur e 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 brigh tener, Tinopal LPW (conidial survival slopes of -2.1 and -1.7 in trial s one and two, respectively), and a clay emulsion (slopes of -2.5 and -2.0) significantly increased survival of conidia compared to the wate r 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 en hanced by the three oil-compatible adjuvants tested (oxybenzone, octyl -salicylate, and ethyl-cinnamate). The use of uv-B protectants in form ulations can increase conidial survival and may enhance the efficacy o f B. bassiana for controlling insect pests in epigeal habitats.