Studies on heat treatment specifications for phytosanitary purposes
Heat treatments can be used as phytosanitary treatments against fruit flies. But several factors can influence the ability of fruit fly larvae to tolerate high temperatures: 1) the heat conducting capacity of the medium in which insects are immersed; 2) the temperature to which larvae have been exposed before the treatment; 3) the rate at which the heat is applied. Studies were done in USA on the influence of heat rates. Hot water treatments of third instar larvae of Anastrepha ludens (EPPO A1 quarantine pest) placed in artificial fruits were applied at different heat rates in the laboratory. Results showed that the 99 % lethal time dose for larvae exposed to 44 °C core temperature in artificial fruits is 61.5 min when a slow heating rate is used (120 min), but only 41.9 min when a fast heating rate is used (15 min). The authors concluded that when designing phytosanitary treatments, the commodity heating rate has to be included in the treatment specifications. So far, most phytosanitary treatment specifications only included a specific temperature with a fixed treatment time. This is felt no longer appropriate, and it is proposed that heat treatments should now indicate a specific temperature and a commodity heat dose which could be expressed in terms of: minimum time necessary to reach the required core temperature within the commodity, and the time during which this core temperature should be maintained.
Sources
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Thomas, D.B.; Shellie, K.C. (2000) Heating rate and induced thermotolerance in Mexican fruit fly (Diptera: Tephritidae) larvae, a quarantine pest of citrus and mangoes.
Journal of Economic Entomology, 93(4), 1373-1379.
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