Toxicological and biochemical analysis of the susceptibility of sylvatic Triatoma infestans from the Andean Valley of Bolivia to organophosphate insecticide

To increase our knowledge of the natural susceptibility of Triatomainfestans to an organophosphate insecticide, we performedtoxicological and biochemical studies on three sylvatic populations from Boliviaand two populations from domestic dwellings from Bolivia and Argentina.Fifty-per-cent lethal doses (LD50) were determined based on the topicalapplication of fenitrothion on first instar nymphs and mortality was assessed at24 h. Both type of populations exhibited LD50ratios significantly higher than 1with a range of the values (1.42-2.47); the maximum value were found in asylvatic (-S) population, Veinte de Octubre-S. Samples were biochemicallyanalysed using a glutathione S-transferase activity assay. The highestsignificant activity was obtained for Veinte de Octubre-S and the lowestactivity was obtained for the reference population (102.69 and 54.23 pmol perminute per mg of protein respectively). Two out of the three sylvaticpopulations (Veinte de Octubre-S and Kirus Mayu-S) exhibited significantlyhigher glutathione S-transferase activity than that of the reference population.Based on this analysis of the natural susceptibility of this organism toorganophosphate insecticides, continental and focal surveys of organophosphatesusceptibility should be conducted to evaluate the evolution and distribution ofthis phenomenon.