Study on the factors affecting mortality of fruit flies in fruits subjected to vapor heat treatment.
Kawai T., Tanno M., Tsuchiya Y.
Author Affiliation: Yokohama Plant Protection Station, 5-57 Kitanaka-dori, Naka-ku, Yokohama 231-0003, Japan.
Research Bulletin of the Plant Protection Service, Japan : 29-34
Abstract : Vapor heat treatment (VHT) is one of the effective plant quarantine treatments against fruit flies in fruits. Three tests were conducted to reveal the factors affecting the mortality of Bactrocera dorsalis eggs in mangoes subjected to VHT. (1) Mortality rates were compared between two different relative humidity conditions during the 10-min holding time wherein the temperature of the innermost pulp is ?46.0°C. Mortality of eggs treated at constant 95%RH was 99.89%, while when the humidity temporarily fell below 90% RH, the mortality was 98.23%. Corresponding to the drop in humidity, temperatures in the outermost pulp dropped temporarily. These results suggest that a drop in humidity during the holding time affects the efficacy of VHT. (2) Mortality rates were compared between different cooling methods following VHT. Mortality was 99.98% by air cooling but 99.53% by hydrocooling. Outermost pulp temperatures dropped more rapidly under hydrocooling than under air cooling. (3) Heating times required to reach 46.0°C were compared between different positions in the innermost pulp of mangoes. Two temperature probes were inserted into a mango on both sides of the flat seed. These mangoes were placed in the VHT chamber to face an airflow on one side. The innermost pulp temperature on the upwind side reached the target temperature in 179.0±0.3 min, but on the downwind side in 180.2±0.3 min (t-test, p0.05).