Cold Treatment: An Effective Post-Harvest Disinfestation Treatment For Bactrocera Tryoni (Diptera: Tephritidae) In 'Gold3' Kiwifruit

Queensland fruit fly (Qfly), Bactrocera tryoni (Froggatt), is a major quarantine pest of fresh horticultural commodity along the eastern coastal region of Australia and restricts market access of its host commodity. Consequently, various post-harvest disinfestation treatments are used to facilitate trade and one such treatment for Qfly is 'cold disinfestation'. Our study evaluated the effect of cold storage as a post-harvest disinfestation treatment for Qfly on 'gold3' kiwifruit (Actinidia chinensis var. gold3-sungold), a cultivar grown in New Zealand. Qfly is not present in New Zealand but due to its close proximity to Australia, New Zealand's trading partners have shown concern that Qfly presents a biosecurity risk to their own industry. Our study specifically aimed to demonstrate how this risk would be addressed. Experiment 1 investigated developmental rate of the individual life stages of Qfly in 'gold3' kiwifruit under optimal Qfly development conditions of 26 +/- 1 degrees C and 65 +/- 5% rh, while experiment 2 focused on determination of the most cold tolerant life stage of Qfly in 'gold3' kiwifruits. Experiment 3 was a large-scale confirmatory trial undertaken using the most cold tolerant life stage. The results revealed that Qfly successfully developed in 'gold3' kiwifruit and that the most-cold tolerant Qfly life stage was the 1st instar. Our study further demonstrated that storage of 'gold3' kiwifruit at 2.5 degrees C (fruit temperature) for a period of >= 12 days resulted in zero Qfly survival. The large-scale verification trial treated 61,412 first instar and confirmed that storage of 'gold3' kiwifruit at 2.5 degrees C for a 14-day period resulted in 99.9951% mortality of first instar at the 95% confidence level, hence demonstrating a probit 8.7 level of efficacy. A 14-day cold storage period was used in this confirmatory trial to ensure additional quarantine security. We recommend that if there was any Qfly infestation on 'gold3' kiwifruit, a post-harvest quarantine treatment of cold storage at 2.5 degrees C (fruit temperature) for a 14-day period must be used to disinfest Qfly from 'gold3' kiwifruit.