Reexamination of Several Rearing Methods for Studying the Life History of Spider Mites (Acari : Tetranychidae)

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Abstract
The commonly-used method for experimental study of spider mite and phytoseiid life histories, namely detached leaves on wet substrates caused temperature variations in the layer where the mites live. Temperature variations between the leaf surface and the ambient (1 cm above the leaf surface) were tested by six different methods, i.e. four detached leaf methods and two live-leaf methods, under conditions of 45-50% RH (measured 1 cm above the leaf surface). Temperatures of detached leaves on wet substrates were always lower than those of the ambient. Use of wet cotton or water-soaked foamed plastic pads caused a temperature difference of about and more than 3.degree.C. On the other hand, the temperatures of live leaf surfaces were not different from those of the ambient. High relative humidity reduced temperature differences between the detached leaf surface on wet substrates and the ambient, so that such variation could be attributed to heat loss by evaporation from the wet substrates. Developmental periods of molting (teliochrysalis) females of Tetranychus urticae Koch observed simultaneously under the same ambient conditions showed that mites on the live leaf developed 1.3 times faster than those on detached leaves on water-soaked foamed plastic pads. This indicated that difference in leaf surface temperatures directly affected mite development. Differences in host plant and leaf side also affected the leaf surface temperature when using detached leaves on wet-substrates.

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