Thermal summation studies of the development of the navel orangeworm,Amyelois transitella(Walker), on almonds were carried out during 1981 and 1982. An upper developmental threshold of 34.4°C was determined from field data. New crop nuts were caged while still attached to the tree and inoculated after hullsplit with 1st-instar larvae. Mean developmental times from egg to adult when reared on new crop nuts were 424 and 427 degree-days C in 1981 and 1982, respectively. Nuts from previous years' crop (“mummies”) were also caged in the field and inoculated with 1st-instar larvae. The mean time required for navel orangeworm development on mummy almonds was 623 degree-days C.