Studies on the environmental factors for the breeding of grain mites. : Part 1. The effects of humidity and moisture contents on the breeding of Tyrophagus dimidiatus

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Other Title
  • コナダニ類の繁殖条件の研究 : I. ケナガコナダニの繁殖と湿度及び水分含量の関係について
  • コナダニ類の繁殖条件の研究-1-
  • コナダニルイ ノ ハンショク ジョウケン ノ ケンキュウ 1

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Experiments were made to observe the effects of environmental humidity and of the moisture contents of various stored food products on the breeding of the grain mite, Tyrophagus dimidiatus. The humidity was regulated by keeping the materials in glass vials containing saturated solutions of various salts, such as K_2CO_3 (46% R.H.), CaCl_2 (53% R.H.), NaCl (70% R.H.), NaNO_3 (77% R.H.) and of water (95% R.H.). All experiments were made at 25℃. Using powdered materials as the food for the mites and relatively low moisture contents, such as laboratory animal food (6.6% water content), shichimipepper (8.8%) or dried yeast (4.4%), breeding of the mites shows the best condition at the highest humidity of 95% R.H. With the dried and sliced fishmeal (kezuribushi), which water content rapidly balances with the relative humidity of the environment, the best breeding of the mites were seen at 85 to 75% R.H. In the case of rice which contained 15.0% of water, less effects of the relative humidiy were seen both on the growth of the mites and on changes of water contents. Water contents of the materials to be tested were also found to affect the breeding of the mites. Both in powdered laboratory animal food in dried yeast, the optimum water content for the growth of the mites was seen at 17.7% and 16.6% respectively, and their breeding seemed to be interfered as it became either lower or higher from the level. By using dried yeast, powder milk and skim milk as the material, experiments were designed to observe the speed of breedings of the mites in the food containing different grades of water contents and kept at different relative humidities. In the initial few weeks, the best breeding was seen in lots with low moisture contents and kept at high relative humidities as well as in those with 18.0% water content and kept at 75% R.H. In the later stages after several weeks, the highest mite counts were seen in those kept at 75% R.H. indifferent from the initial water contents of the foods. Although their relative effects seem to differ greatly by the nature of the food to be tested, through these experiments, it has been demonstrated that both relative humidity of the environment and the moisture content of the materials are the essential factors for the breeding of the mites. For the purpose of preventing the stored food products and some drugs from breeding of the mites, either dessication of the materials or the storage at low humidity was found to be the effective measure.

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