Effects of ionizing energy on fruit flies and seed weevil in Australian mangoes

Irradiation was evaluated as a quarantine measure for the disinfestation of Australian mangoes against two species of fruit fly, Bactrocera (=Dacus) tryoni (Froggatt) and B, jarvisi (Tryon), and the mango seed weevil, Sternochaetus mangiferae (Fabricius). For the fruit flies, the third instar stage was determined as the most tolerant of irradiation, but disinfestation trials were also undertaken against mature eggs as the stage most likely to be present in any infested fruit at the time of treatment. A dose range of 74-101 Gy on the ''Kensington'' variety of mango prevented the emergence of adult flies, but large numbers of treated larvae and some eggs developed to the pupal stage. This places important emphasis on the field control of fruit flies if detection of still living larvae in fruit at inspection is to be avoided. Disinfestation trials on the mango seed weevil were complicated by the inability to culture this insect in the laboratory. This necessitated the use of naturally infested fruit of the ''common'' variety and precluded trial work on specific stages of known age. A dose range of 298-339 Gy (nominally a minimum of 300 Gy) prevented adult emergence and ensured 100% mortality by 8 months on the samples treated. The slow life cycle of the seed weevil requires that assessment of mortality be delayed by a minimum of 1 month, and for full mortality up to 6-8 months. The presence of live insects in irradiated fruit causes problems if detected at inspection unless export fruit is obtained from weevil free orchards. No significant fruit damage would be expected at a fruit fly treatment range of 100-200 Gy, but the maximum/minimum ratio for weevil treated fruit would need to be minimized as the treatment level is near the threshold for damage to the ''Kensington'' variety of mango. (author). 15 refs, 1 fig., 3 tabs