Abstract Bactericera cockerelli Sulc (Hemiptera: Psylloidea: Triozidae), also known as the potato psyllid, is a pest of pepper and potato crops in northern Mexico. Growers control it by applying insecticides, without knowing the tolerance or resistance levels to these pesticides. The goal of this study was to determine the resistance ratios of several populations of B. cockerelli from regions of northern Mexico. Three populations of B. cockerelli were collected from sample sites at Coahuila—Nuevo Leon, San Luis Potosi, and Aguascalientes and compared with a laboratory susceptible line. Results indicated that populations from Aguascalientes had resistance ratios of 1.69-, 1.26-, and 1.00-fold for the insecticides abamectin, endosulfan, and imidacloprid, respectively. The corresponding ratios were 10.72-, 2.52-, and 3.75-fold for the San Luis Potosi population and 2.57-, 3.75-, and 4.22-fold for the Coahuila—Nuevo Leon population. We conclude that the B. cockerelli population of only San Luis Potosi was res...