The otitid fly, Tetanops myopaeformis, is the primary insect pest of U. S. sugar beets, affecting approximately 500,000 hectares. Mexican marigold, Tagetes minuta, has been shown to have nematicidal properties and some promise for managing sugarbeet cyst nematode. We evaluated T. minuta toxicity for T. myopaeformis in the laboratory with diapausing third instar T. myopaeformis. A steam distilled extract and mulch preparation of T. minuta shoots were assayed with larvae to determine the LC50 and LT50. Then, the LC20 of steam distillate was combined with conidia of a Metarhizium anisopliae (MA1200) and a Beauveria bassiana (TM28) in a soil-based bioassay to determine effects of the distillate on fungal efficacy. These fungi are under study by the second author as candidate mycoinsecticides against the insect. Bioassays in three soil types, from three T. myopaeformis infested locations, were conducted with diapausing third instar larvae. Larval mortality from Metarhizium infection, but not from Beauveria infection, increased in the presence of Tagetes extract, and also the emulsifier. Conidial germination under semi-commercial conditions was determined. Effects of the extract on in vitro conidial germination and hyphal growth were also examined.
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