To overcome constraints on ionising radiation and cold treatment as stand-alone disinfestation treatments for Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) in citrus fruit, the efficacy of a combination treatment consisting of ionising radiation and cold, both at reduced doses, was tested at the probit-9 level. Earlier research indicated that combination treatments involving ionising radiation and cold suppressed larvae and their successive development stages more effectively than the individual treatments. The probit-9 level efficacy (at least 93 613 insects) of a treatment combination comprising 60Gyof ionising radiation followed by cold exposure for 16 days at 2.5 °C was evaluated. A total of 104 617 mature, fifth instars was treated. Larval mortality was 99.7%and 50.2%of the subsequent pupae died. A total of 143 moths with a sex ratio of one female to 7.9 males eclosed. Only 4.8%of the moths were able to fly. No eggs were produced by the moths in mating studies. The probit-9 level efficacy of the combination treatment was validated, indicating that it meets the efficacy requirements for utilisation as a phytosanitary disinfestation treatment for T. leucotreta in citrus fruit in international trade.