Cold treatment: an effective post‐harvest disinfestation treatment for Bactrocera tryoni (Diptera: Tephritidae) in ‘gold3’ kiwifruit

Abstract

AbstractQueensland 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°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°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°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°C (fruit temperature) for a 14‐day period must be used to disinfest Qfly from ‘gold3’ kiwifruit.