Study of Aedes aegypti resistance to Bacillus thuringiensis var. israelensis.
INTRODUCTION: Prolonged use of insecticides has led to resistance development in different mosquito species including Aedes aegypti, although there is no report of resistance to Bacillus thuringiensis var. israelensis so far. OBJECTIVES: To evaluate resistance to Bacillus thuringiensis var. israelensis in Aedes aegypti populations from places where fluid preparation Bactivec (made in Labiofam company) has been applied, and in lab strains under selection. METHODS: Larvae were collected in three municipalities of the City of Havana province to settle Aedes aegypti colonies in the laboratory, which were compared with reference strain called Rockefeller in terms of susceptibility to Bacillus thuringiensis. The selection experiment was performed by exposing successive generations of a strain susceptible to lethal dose 90 of this biolarvicide. RESULTS: Resistance index 50 for strains from Plaza, Cerro and Boyeros was 1.07, 0.66 and 0.81 respectively, so they may be considered as susceptible strains. The strain exposed to intensive selection pressure with the biolarvicide showed resistance indexes 50 and 95 equal to 2.7 and 4.6 respectively. The smallest regression line slope was found in the selection strain, which indicated a greater genetic variability in this population. CONCLUSIONS: these results support the use of Bacillus thuringiensis var. Israelensis as an alternative for management of immature Aedes aegyptis without any evidence whatsoever of emerging resistance in the field population, but some adequate management strategies should be drawn, taking into account the vector's potentialities to acquire it.