The production of crystals and spores ofBacillus thuringiensis var.israelensis was studied under different aeration conditions. The results with 4 l batch cultures showed that for O2 non-limited, cultures cell yield, toxin production and spore count were constant for all oxygen transfer rates (OTR). Under O2 limitation, °-endotoxin concentrations and spore counts were lower than those obtained in non-limited cultures. In addition, δ-endotoxin yields diminished under O2 limitation, suggesting that the toxin synthesis mechanism could have been affected.

Chagas disease constitutes a major human health problem in most Latin American countries. This endemic disease is transmitted by several species of triatomine bugs, the most important being Triatoma infestans (Klug). In this article, we report on the selection of strains of the entomopathogenic fungus Beauveria bassiana (Bals.) Vuill. virulent to T. infestans for possible use as bioinsecticides. Four strains of B. hassiana isolated from Argentina (Bb 1, 10, 25, and 65) were evaluated. To calculate mortality and mean lethal time, nymphs and adults of T. infestans were treated with conidia produced on complete agar medium and wheat brain and rice husk medium (WH). The LD50 for nymphs and adults of T. infestans was calculated. The effect of different temperatures (18, 22, 26, 30, and 34 degrees C) and relative humidities (35 and 90% RH) on mortality of nymphs were studied. We evaluated the compatibility of strains with Deltamethrin and Beta-Cypermethrin. Although the strain Bb 25 failed to grow on WH, the other three strains showed similar mortality values independent of the culture medium used to grow the microorganisms. The lowest LD50 values for nymphs were obtained with the strains Bb 10 and 65 and for adults were Bb 1, 10, and 65. The highest mean mortality was obtained with strain Bb 10, and among temperatures the highest mean mortality was observed at 26 degrees C. Relative humidity did not affect the mortality of T. infestans nymphs with all strains and temperatures assayed. Deltamethrin did not affect any of the three strains for the four studied doses, and Beta-Cypermethrin could be used in combination with the fungus only at low doses. The strain Bb 10 was selected for future assays under natural climatic conditions.

No abstract