Efficacy of BotaniGard^® against the mushroom phorid fly Megaselia halterata

Megaselia halterata (Wood) (Diptera: Phoridae) is a major pest of cultivated white button mushrooms, Agaricus bisporus (J.E.Lange) Emil J. Imbach (Agaricales: Agaricaceae), in the United States. The incidence and severity of M. halterata have been increasing in recent years, possibly due to the removal of certain chemical pesticides from tolerance by the EPA. Farmers’ demand for alternative control measures resulted in a label extension of the fungal biopesticide BotaniGard^® ES, which contains viable spores of Beauveria bassiana (GHA strain), for use in mushroom crops. Here we describe laboratory bioassays to evaluate the efficacy of the label recommended dose of the abovementioned commercial biopesticide for control of immature and adult stages of M. halterata. According to our results, eggs and larvae of M. halterata were not susceptible to infection by B. bassiana whereas pupae displayed a partial susceptibility with mortality reaching up to 65%. Concerning adults of M. halterata exposure for 60 min to a paper surface sprayed with the registered label application rate of BotaniGard^® ES led to 100% mortality within a period of 16 days and a mean survival time of 8.13 days, which differed significantly from the control batch, but unlikely to result in meaningful control of phorid populations in the field. Further studies should be examined to increase efficacy of the formulated product against immature and adult stages of M. halterata.