The main objective of the present work was to study the development of
resistance in two mite species infesting stored products, namely, the grain and
flour mites Aleuroglyphus ovatus (Troupeau 1878) and Tyrophagus
pufrescentiae (Schrank 1781), to phosphine, carbon dioxide and their mixtures
in the laboratory.
Adults of the investigated mite species were exposed for 17 generations
to a fixed concentration of phosphine (200 vpm). a controlled atmosphere
containing 46% co2 and a combination of loo vpm PH3 + 23% co2 at 26±1°C
and 85±5% RH at varying exposure periods in order to select strains resistant to
phosphine, carbon dioxide and their mixtures.
Selection pressure was carried out at the median lethal dose/times
inducing mortalities between 50-70%.
Results showed that the tolerance ratio (TR) at the 17th generation of A.
ovatus was 1.2, 1.1 and I4 fold for PH-TS, C02-TS and PH3+CO-TS at LT5O-
level, respectively.
, In case of T putrescenriae. it was 1 3. 1.3 and 1.8 fold for the various
strains;, respectively.
This result indicated that the two mite species have slow capability to
develop resistance to the fumigants phosphinc. carbon dioxide and their
mixtures Thus could be duc to the fact that these two mite species arc belonging
to Astigmata and might hىave lo genetic potential to build up resistance to the
fumigants under study
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