Field and Laboratory Evaluation of a Bacillus thuringiensis var. israelensis Formulation for Control of Fly Pests of Mushrooms

A formulation of Bacillus thuringiensis var. israelensis (Gold berg), ABG-6193, was tested for toxicity to larvae of fly pests of commercial mushrooms (Agaricus bisporus (Lange) Imbach). Concentration-mortality tests with ABG-6193 and Lycoriella mali (Fitch) larvae indicate that the LD50 in compost is about four times higher than the LD50 in agar. In six of seven field tests, ABG-6193 controlled both L. mali and Megaselia halterata (Wood) as well as or better than registered larvicides and adulticides. Mushroom yields in ABG-6193 treated houses averaged 3.5 kg/m2 higher than in grower-treated houses for all tests with yield data. Causes of the single field test control failure were investigated in laboratory experiments. Heat treatments lowered protein content and toxicity of the formulation; however, this occurred at temperatures not encountered in mushroom culture. Incubation with concentrations of sodium hypochlorite solubilized the protein toxins and reduced toxicity in bioassays. Excessive chlorine use by the grower probably resulted in degradation of ABG-6193 toxins. ABG-6193 or similar formulations have potential for pest management in commercial mushrooms.