The Asian citrus psyllid, Diaphorina citri Kuwayama, vectors the bacterium ‘Candidatus Liberibacter asiaticus’ responsible for the huanglongbing (HLB) disease. In Mexico, economic losses caused by HLB severely affect the citrus industry. Despite the threat that the presence of D. citri implies, due to its invasive characteristics, there are few ecological and biological studies addressing its adaptation to new and different environments in Mexico. Based on the temperature-size rule, stating smaller adult size at higher rearing temperatures, the aim of this study was to evaluate D. citri's body size variation at different temperatures related to an elevation gradient. Adults were collected at four different elevations in the states of Jalisco and Colima, Mexico. Right forewing length and width as well as prothorax width and right antenna length were measured. Statistical differences between the sexes were analyzed by a multivariate analysis using Hotelling's T² and Kruskal—Wallis nonparametric test to evaluate body size variation between elevations followed by a Nemenyi's pairwise comparison test. To evaluate relationships between size variation and elevation, a χ² independence test was performed. Females were shown to be statistically larger than males. All body structures except the prothorax were shown to be larger at location El Arenal (higher elevation) and smaller at location Tecomán (lower elevation). Forewing length and width best explained the differences observed between the sexes and at the four locations, showing that the temperature-size rule applies in this case.