Adult culicoides variipennis sonorensis Wirth & Jones were tested using fluorescence spectrophotometry to determine whether age or sex influenced fluorescence. Males and nulliparous females 0.5, 2.5, and 5.5 d after eclosion were processed, as were uniparous and biparous females 14 d after eclosion. Variability among insects within a sex and age group was moderately high. Males and nulliparous females showed significantly greater fluorescence when very young (0.5 d old). Parous females had significantly lower levels of fluorescence compared with younger nulliparous females and males, but uniparous females could not be differentiated from biparous females of the same absolute age. Fluorescence as applied here appears to have limited utility as a tool for age determination in this vector species.