Insecticide bioassays associated with colorimetric testes were used to determine the diagnostic concentrations of pirimicarb for insecticide resistance detection in Myzus persicae populations from potato crops. The aphids were randomly collected on potato plants of commercial crops in Curitiba, Piraí do Sul and Contenda, in Paraná State and Ibicoara in Bahia state, from 1994 to 1996. The LC50 was estimated by submitting the aphids to bioassay with increasing concentrations of pirimicarb. Dead and live aphids from the 0.0125; 0.025; 0.05 and 0.1% (g/100ml) insecticide treatments were frozen after one hour of the bioassay and submitted to the evaluation of total esterase by colorimetric assays. Mortality was low at 0.0125%, but at 0.1% it reached 100% of the populations; thus, indicating that the diagnostic concentration is within this range. A significant difference was found between mortality caused by 0.025 and 0.05% pirimicarb in the same population, but not between populations collected from different areas. The 0.05% primicarb concentrations caused mortality of nearly 50% of high resistant individuals (R2), 72.0%of the moderately resistant populations (R1) and 89.7% of susceptible ones (S). The determination of this diagnostic concentration is useful for M. persicae resistance management programs because all individuals can be tested at this single appropriate concentration and low resistance frequencies can be detected in the population.
Insecta; green peach aphid; insecticide resistance; insecticide bioassays; colorimetric assays; pirimicarb; diagnostic concentration
