SUMMARYThree groups of honey bee colonies (N = 30) were overwintered on a mountainside (2800 M) in northeastern Mexico. Infestation levels of Acarapis woodi in the three groups averaged 0, 28.2 and 86.0 % for the control, moderately, and heavily infested colonies, respectively. Heavily infested colonies were 28 % smaller than controls (P < 0.01) in the fall. Adjusting for this, heavily infested colonies lost significantly more bees than either the moderately infested group, or the controls (P < 0.0001). Both the moderately and heavily infested groups of bees had less brood than controls at the end of the test (P < 0.02 and P < 0.01 respectively). Similarly, honey consumption was higher in the heavily infested group (P < 0.04). Infestation levels were negatively correlated with colony size at the beginning of the test (P < 0.05) and at its end (P < 0.001).