Postharvest phytosanitary disinfestation of Thaumatotibia leucotreta (Lepidoptera: Tortricidae) in citrus fruit: determination of ionising radiation and cold treatment conditions for inclusion in a combination treatment

Postharvest disinfestation of Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) in citrus fruit can be achieved through cold treatment, but chilling injury becomes increasingly problematic with lower temperature and longer exposure to the treatment. Ionising radiation is an alternative treatment, but also has a dose dependent negative effect on fruit quality. The potential of including both a reduced radiation dose and a less detrimental cold treatment in a combination treatment was assessed. The effects of 40 to 70 Gy radiation and cold treatments of 0.6 degrees C to 7.0 degrees C for periods of 10 to 22 days by themselves and in combination, were investigated on mature larvae in artificial rearing diet. It was demonstrated that various combinations of the two methods can act together to potentially provide adequate control, with the prospect of moderated fruit quality effects due to the reduced intensity of the component treatments. A combination treatment consisting of 60 Gy followed by 16 days at 2.5 degrees C was identified for further evaluation as a combination treatment that could potentially be validated at the probit-9 level of efficacy.