Selection of Beauveria bassiana and Metarhizium anisopliae isolates to control Triatoma infestans

RESUMO

Twenty three isolates of Beauveria bassiana and 13 isolates of Metarhizium anisopliae were tested on third instar nymphs of Triatoma infestans, a serious vector of Chagas disease. Pathogenicity tests at saturated humidity showed that this insect is very susceptible to fungal infection. At lower relative humidity (50 per cent), conditions expected in the vector microhabitat, virulence was significantly different among isolates. Cumulative mortality 15 days after treatment varied from 17.5 to 97.5 per cent and estimates of 50 per cent survival time varied from 6 to 11 days. Maintaining lower relative humidity, four B. bassiana and two M. anisopliae isolates were selected for analysis of virulence at different conidial concentrations and temperatures. Lethal concentration sufficient to kill 50 per cent of insects (LC50) varied from 7.1x10 5 to 4.3x10 6 conidia/ml, for a B. bassiana isolate (CG 14) and a M. anisopliae isolate (CG 491) respectively. Most isolates, particularly B. bassiana isolates CG 24 and CG 306, proved to be more virulent at 25 and 30ºC, compared to 15 and 20ºC. The differential virulence at 50 per cent humidity observed among some B. bassiana isolates was not correlated to phenetic groups in cluster analysis of RAPD markers. In fact, the B. bassiana isolates analyzed presented a high homogeneity (>73 per cent similarity).