The objective of this research was to evaluate the relationship between the total activity of carboxylesterase and the resistance of M. persicae populations to pirimicarb. The aphids were collected on potato plants in Contenda and Piraí do Sul, PR and Ibicoara, BA, Brazil. For the bioassay, five replicates for each concentration were prepared with 10 aphids placed in plastic vials with a fine fabric mesh on the bottom, and dipped into pirimicarb concentrations (%) at 0.0031; 0.0062; 0.0125; 0.025; 0.05, and 0.1%, during 10 seconds, then dried on filter paper. After 1h inside a 25°C chamber, the aphids were examined under a stereomicroscope, recording the number of dead insects. The carboxylesterase activity was assessed by in vitro colorimetric technique. A simple correlation was established between the results of the LC50 bioassay and the frequency of M. persicae resistant variants. According to the absorbance level, the aphids were classified as variants S; S/R1 (S or R1); R1; R1/R2 (R1 or R2); R2 and R3, respectively susceptible; partially resistant, resistant and highly resistant. It was found a significant positive correlation between the LC50 and the frequency of R2 forms and a significant negative correlation between LC50 and the frequency of S and S/R1 forms. The colorimetric data supported the bioassay results, indicating that the bioassay was precise enough to determine either populations with high frequency of susceptible individuals or population with high proportion of resistant and highly resistant individuals.
CL50; green peach aphid; pirimicarb resistance
