Vapor heat mortality tests on the eggs of the Oriental fruit fly, Bactrocera dorsalis, infesting different sizes and varieties of fresh mango.
Yoshinaga M., Masaki S., Dohino T.
Author Affiliation: Research Division, Yokohama Plant Protection Station, 1-16-10 Shin-Yamashita, Naka-ku, Yokohama 231-0801, Japan.
Research Bulletin of the Plant Protection Service, Japan : 41-47
Abstract : A series of vapor heat treatment tests was conducted on mango fruits infested with eggs of the Oriental fruit fly, Bactrocera dorsalis (Hendel), to clarify the effect of the fruit size and cultivated variety factor on the mortality of the B. dorsalis eggs. In the mortality test by fruit size, Carabao mangoes in three different sizes (S, M and L) infested with the eggs were heated to raise the fruit pulp temperature of each size to 44.0, 45.0, 45.5, 46.0, 46.5 and 47.0°C inside the vapor heat treatment chamber set at 49.0°C and relative humidity 95%. Then the mortality of the eggs among the different fruit sizes was compared. The results showed that mortality at each target temperature differed among the sizes: the larger the fruit size, the higher the mortality. Larger fruits had slower increases in pulp temperature, which meant longer exposure to high temperatures. This was thought to be the cause of the higher mortality. In the mortality test by variety, Kensington Pride and Tommy Atkins mangoes were used. Vapor heat treatment was applied under the same conditions as above. In order to eliminate the size effect on mortality, mango fruits of nearly the same weight were selected for the test. Probit analysis showed that eggs in the Tommy Atkins variety were significantly more likely to be disinfested (LT90, LT95), revealing that variety affects mortality. However, 100% mortality was obtained at 46.5°C or higher temperatures for both varieties. It was thought that the effect of variety was reduced under severe conditions close to complete-kill conditions. The two varieties of fruit had nearly the same rate of temperature increase, suggesting the possibility that some differing factor affecting mortality may exist between varieties, other than the rate of temperature increase.