Methyl bromide fumigation and cold storage for disinfestation of Granny Smith apples against Queensland and Mediterranean fruit flies

Abstract

Granny Smith apples infested with eggs, young or old larvae of Queensland fruit fly, Dacus tryoni (Froggatt.), or Mediterranean fruit fly, Ceratitis capitata (Wiedeman.), were fumigated with 32 g/m3 methyl bromide (MB) for 2 h at 17¦C or 10¦C followed by cold storage at 1.5 ¦ 0.5¦C for periods from 0-1 0 d. With both insects, eggs were recognized as the most tolerant stage. MB alone was ineffective in completely killing any stage, and an additional eight days' cold storage was established as a conservative minimum time to give nil survivors in the most tolerant stage. A high level of security was subsequently demonstrated by the fumigation, in three trials, of at least 10 000 insects at the egg stage and none of them surviving. Initial MB residues ranged from 4.75-3.70 ¦g/g at 10¦C and 17¦C, respectively. During subsequent storage at 1.5¦C residues declined, the data indicating that more than 60% of the MB reacted in situ with the fruit components. MB residues were not detected 7 d after fumigation. With an aeration time of 2 h at the fumigation temperatures, a period of 3-7 d at 15¦C is necessary to avoid MB residues exceeding the maximum residue limit of 0.5 ¦g/g recommended by the National Health and Medical Research Council of Australia (NHMRC). At no time did inorganic residues exceed the maximum residue limit of 20 ¦g/g of the NHMRC and Codex, nor the 5 ¦g/g of the United States Food and Drug Administration.