The number of feeding instars of Marmara gulosa Guillén & Davis (Lepidoptera: Gracillariidae), a pest on citrus in the southwestern United States, was investigated from laboratory and field samples. Larvae passed through four to seven feeding instars before the final transitional and spinning instars. An influence of temperature on the number of feeding instars was observed, with low temperatures increasing the proportion of larvae with a higher number of instars. Characterization of instars by the width of the larval head capsule was attempted, and major differences in head capsule width were observed between the same instars of larvae passing through four, five, and six feeding instars. Growth ratios of head capsule width between successive instars were higher for larvae with fewer instars than for those with a higher number, and last feeding instars for each group reached a similar final size.