Tuesday, 16 November 2004

Efficiency of two formulations of Bacillus thuringiensis var. israelensis for the control of Anopheles aquasalis (Diptera: Culicidae) larvae in four salt concentrations

Frances Rowland Osborn, fosborn2001@yahoo.com1, Melfran Herrera2, Cruz Gomez2, and Armando Salazar2. (1) Universidad de Oriente, Instituto de Investigaciones en Biomedicina y Ciencias Aplicadas, Cerro del Medio, Cumana, Sucre, Venezuela, (2) Gerencia de Saneamiento Ambiental y Malariologia Region XI, Via Canchuchu, Carupano, Sucre, Venezuela

The effectiveness of bacterial formulations for the control of pests may vary depending on environmental conditions. The larvae of Anopheles aquasalis, the principal malaria vector in Sucre state, Venezuela, prefer salt concentrations of between 10 and 20 ppt. The larvicidal effect of two formulations of Bacillus thuringiensis var. israelensis (Vectobac-AS and Bactivec), on An. aquasalis at salt concentrations of de 0, 5, 10 and 20 ppt was investigated; five concentrations of each product for each salt solution were prepared in potable water with six replicas per treatment plus controls, and 10 early fourth instars were placed in 100 ml of the prepared solutions. Mortality was noted 24 hours after the beginning of the experiment. The lethal concentrations (LC50 and LC95) were calculated for each product at each salt level: Vectobac-AS, 0.20 and 0.67 ppm; 0.20 and 0.88 ppm; 0.15 and 0.80 ppm; 0.19 and 0.85 ppm for 0, 5, 10 and 20 ppt of salt respectively and Bactivec, 0.89 and 5.05 ppm; 1.38 and 6.62 ppm; 1.54 and 7.53 ppm; 2.24 and 10.05 ppm respectively for the same salt concentrations. Both the LC50 and the LC95 were significantly higher for Bactivec compared to Vectobac-AS for all the salt concentrations tested. The LC50 and LC95 for Vectobac-AS were not affected by salt, whereas for Bactivec they increased with an increase in salt concentration. In conclusion, the use of Vectobac-AS should be preferred to that of Bactivec for An. aquasalis control, especially in salty breeding grounds.

Species 1: Diptera Culicidae Anopheles aquasalis (salt water malaria mosquito)
Species 2: Eubacteriales Bacillaceae Bacillus thuringiensis
Keywords: lethal concentrations

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