Six studies were conducted to quantify the relationship between fruit surface damage of ‘Hamlin’ orange,Citrus sinensis, and population denisty of the citrus rust mite,Phyllocoptruta oleivora(Ashmead). Over time, the damage rate per mite-day increased in sigmoid fashion mainlyas a result of a sigmoid increase in cumulative mite-days. The sigmoid increase in cumulative mite-days resulted from the single-peaked, more or less symmetrically shaped mite population growth. Increasing fruit maturity increased susceptibility to mite feeding. This was indicated by a decline in mite-days required to cause a given percentage of surface damage as fruit maturity increased. Tree age and grove location did not seem to have obvious effect on the general trend in damage rate. A mathematical model was developed to describe the relationship between cumulative damage and cumulative mite-days. The model could be used to predict fruit surface damage based on mite population data.