Methyl bromide fumigation and delayed mortality: safe trade of live pests?
Live organisms intercepted from treated commodities during phytosanitary inspections usually arouse suspicions of treatment failure, sub-standard treatment application, or post-treatment infestation. The additional possibility that some treatments could kill slowly, meaning commodities might be inspected before pests have succumbed, is seldom considered for treatments other than irradiation. We used a novel biochemical viability assay to measure delays between methyl bromide fumigation and mortality of dipteran eggs, and evaluated the correspondence between egg viability and egg morphological features. Our experimental conditions simulated shipping of rock melons from Australia to New Zealand by sea and air. No eggs survived fumigation, but they took 3-20 days to die, whereas phytosanitary inspections of rock melons occur within 2-7 days. Delays were not influenced by methyl bromide concentration, but were significantly lengthened by cooler storage temperatures. Methyl bromide's preservative effects delayed degradation of egg morphology, so the biochemical assay detected mortality long before morphological signs of egg death appeared. The results show that commodities subjected to effective methyl bromide treatments are at risk of being inspected before all pests have either died, or started to exhibit morphological signs of death. This could cause commodities to be unnecessarily rejected by quarantine authorities. Better methods than inspection for live pests are needed to assist authorities to gain assurance that treated commodities have been effectively disinfested. These could be developed by exploiting biochemical responses of pests and commodities to treatments.
AgResearch, Lincoln, Private Bag 4749, Canterbury, 8140 New Zealand.
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Phillips
AgResearch, Lincoln, Private Bag 4749, Canterbury, 8140 New Zealand.
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Iline
AgResearch, Lincoln, Private Bag 4749, Canterbury, 8140 New Zealand.
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Novoselov
AgResearch, Lincoln, Private Bag 4749, Canterbury, 8140 New Zealand.
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McNeill
AgResearch, Lincoln, Private Bag 4749, Canterbury, 8140 New Zealand.
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Richards
AgResearch, Lincoln, Private Bag 4749, Canterbury, 8140 New Zealand.
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van Koten
Ministry for Primary Industries, PO Box 2526, Wellington, 6140 New Zealand.
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Stephenson
ATP; Insect mortality; Methyl bromide; Phytosanitary inspection; Time to die