Colaspis bridarollii (Bechyné), is one of the main pests of potatoes in Buenos Aires province, Argentina. The adult longevity, reproductive biology, and pupation period of C. bridarollii were studied in the laboratory; seasonal phenology and larval feeding damage were examined in potatoes in the field from 1991 to 1993. Laboratory studies showed that there was no significant difference between female and male mean longevity (38.63 and 39.78 d, respectively). Total mean fecundity was 402.73 eggs per female, and the mean number of eggs per d per female was 27.76. Mean number of egg clutches per female was 5.68 with a mean number of 71 eggs per clutch. Mean incubation period was 7.80 d and 74.50% of eggs hatched. Field sampling results showed that C. bridarollii and potato crop phenologies are well synchronized. Adults were present in the potato fields from the end of December to mid March, and the second and third instars reached peak densities in March and April, coincident with the major feeding damage to tubers.