Citrus rust mites were cultured and acclimatized on green, coastal lemon fruit and subjected to 6 constant relative humidities ranging from 15–90% RH (±5%) each at 5 constant temperatures ranging from 15–35°C (±1%). We achieved the desired humidity control at the different temperatures by means of an original air-flow system without exposing the mites to an accumulation of toxic gases which evolve naturally from lemons. Initial and terminal mite counts provided data on population growth rate under each condition.A regression formula (k= −0.709983−1.412307H+0.124868HT−0.002545HT2) was developed to calculate the association between population growth rate (k) and constant conditions of temperature (T) and humidity (H). The correlation found between observed growth rate and the calculated growth rate of the T-H model was significant at the 0.1% level. Both temperature, a quadratic factor, and humidity, a linear factor, appear to strongly affect the ability of the citrus rust mite to increase in numbers. The theoretical optimal temperature (24.5°C) and limiting temperatures (17.6 and 31.4°C) as well as lethal and limiting humidity levels, depending on temperature, were also derived from the regression equation.