Surface inoculation dose–response and time–response bioassays and detached fruit bioassays were conducted with a novel South African isolate of the Cryptophlebia leucotreta granulovirus (CrleGV-SA) against Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Noctuidae) neonate larvae. LC50 and LC90 values were estimated to be 4.095 × 103 and 1.185 × 105 OBs ml−1, respectively. LT50 and LT90 values were estimated to be 4 days 22 h and 7 days 8 h, respectively, categorising the virus as a fast or type 2 granulovirus. There was a conspicuous difference in behaviour between larvae on inoculated diet and untreated diet, resulting in a significant reduction in penetration of diet. Bioassays on detached Navel oranges revealed LC50 and LC90 values of 9.310 × 107 and 1.515 × 109 OBs ml−1, when using data on numbers of larvae per fruit rather than on numbers of infested fruit. Field trials will be conducted.