Yellow sticky card traps were assessed as a tool for estimating absolute densities of adult Diaphorina citri Kuwayama (Hemiptera: Psyllidae) in citrus. Weekly trapping was conducted in young and mature trees with traps deployed directly in trees, one trap per tree. In addition, a comparison was made between one and three traps per tree in the mature trees. Solar radiation was positively correlated with numbers of adults trapped per week in both groups of trees. Air temperature was positively correlated with captures of adults in the mature trees. The value of traps as indicators of absolute densities of adults was therefore reduced by changes in sunlight and temperature. Captures of adults were not reduced by rain. A positive correlation was found for data from the young trees between trap captures of adults and maximum daily wind speed. Significant correlations were found between numbers of adults on leaves and traps. However, little confidence could be placed on individual predictions of adult densities on leaves based on numbers of adults on traps. Increasing the number of traps per tree from one to three did not improve individual estimates, although detection of adults in trees was improved using three traps when adult population levels were low. A better quantitative relationship between adults on traps and leaves might have been determined if greater sample sizes had been used to estimate densities. Regardless, day-to-day differences in sunlight and air temperature will influence numbers of adults captured on traps, thus reducing the value of traps as indicators of absolute densities.